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rust/rust/704858caa7ac7b8564d87defbbca9dcbe7d31b33/./library/core/src/slice/mod.rs
blob: f787b7994ba9d731c821c1eecdf1456eb0a65645 [file]
//! Slice management and manipulation.
//!
//! For more details see [`std::slice`].
//!
//! [`std::slice`]: ../../std/slice/index.html
#![stable(feature = "rust1", since = "1.0.0")]
use crate::clone::TrivialClone;
use crate::cmp::Ordering::{self, Equal, Greater, Less};
use crate::intrinsics::{exact_div, unchecked_sub};
use crate::marker::Destruct;
use crate::mem::{self, MaybeUninit, SizedTypeProperties};
use crate::num::NonZero;
use crate::ops::{OneSidedRange, OneSidedRangeBound, Range, RangeBounds, RangeInclusive};
use crate::panic::const_panic;
use crate::simd::{self, Simd};
use crate::ub_checks::assert_unsafe_precondition;
use crate::{fmt, hint, ptr, range, slice};
#[unstable(
feature = "slice_internals",
issue = "none",
reason = "exposed from core to be reused in std; use the memchr crate"
)]
#[doc(hidden)]
/// Pure Rust memchr implementation, taken from rust-memchr
pub mod memchr;
#[unstable(
feature = "slice_internals",
issue = "none",
reason = "exposed from core to be reused in std;"
)]
#[doc(hidden)]
pub mod sort;
mod ascii;
mod cmp;
pub(crate) mod index;
mod iter;
mod raw;
mod rotate;
mod specialize;
#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
pub use ascii::EscapeAscii;
#[unstable(feature = "u8_split_ascii_whitespace", issue = "147878")]
pub use ascii::SplitAsciiWhitespace;
#[unstable(feature = "str_internals", issue = "none")]
#[doc(hidden)]
pub use ascii::is_ascii_simple;
#[stable(feature = "slice_get_slice", since = "1.28.0")]
pub use index::SliceIndex;
#[unstable(feature = "slice_range", issue = "76393")]
pub use index::{range, try_range};
#[stable(feature = "array_windows", since = "1.94.0")]
pub use iter::ArrayWindows;
#[stable(feature = "slice_group_by", since = "1.77.0")]
pub use iter::{ChunkBy, ChunkByMut};
#[stable(feature = "rust1", since = "1.0.0")]
pub use iter::{Chunks, ChunksMut, Windows};
#[stable(feature = "chunks_exact", since = "1.31.0")]
pub use iter::{ChunksExact, ChunksExactMut};
#[stable(feature = "rust1", since = "1.0.0")]
pub use iter::{Iter, IterMut};
#[stable(feature = "rchunks", since = "1.31.0")]
pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
#[stable(feature = "slice_rsplit", since = "1.27.0")]
pub use iter::{RSplit, RSplitMut};
#[stable(feature = "rust1", since = "1.0.0")]
pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
#[stable(feature = "split_inclusive", since = "1.51.0")]
pub use iter::{SplitInclusive, SplitInclusiveMut};
#[stable(feature = "from_ref", since = "1.28.0")]
pub use raw::{from_mut, from_ref};
#[unstable(feature = "slice_from_ptr_range", issue = "89792")]
pub use raw::{from_mut_ptr_range, from_ptr_range};
#[stable(feature = "rust1", since = "1.0.0")]
pub use raw::{from_raw_parts, from_raw_parts_mut};
/// Calculates the direction and split point of a one-sided range.
///
/// This is a helper function for `split_off` and `split_off_mut` that returns
/// the direction of the split (front or back) as well as the index at
/// which to split. Returns `None` if the split index would overflow.
#[inline]
fn split_point_of(range: impl OneSidedRange<usize>) -> Option<(Direction, usize)> {
use OneSidedRangeBound::{End, EndInclusive, StartInclusive};
Some(match range.bound() {
(StartInclusive, i) => (Direction::Back, i),
(End, i) => (Direction::Front, i),
(EndInclusive, i) => (Direction::Front, i.checked_add(1)?),
})
}
enum Direction {
Front,
Back,
}
impl<T> [T] {
/// Returns the number of elements in the slice.
///
/// # Examples
///
/// ```
/// let a = [1, 2, 3];
/// assert_eq!(a.len(), 3);
/// ```
#[lang = "slice_len_fn"]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
#[rustc_no_implicit_autorefs]
#[inline]
#[must_use]
pub const fn len(&self) -> usize {
ptr::metadata(self)
}
/// Returns `true` if the slice has a length of 0.
///
/// # Examples
///
/// ```
/// let a = [1, 2, 3];
/// assert!(!a.is_empty());
///
/// let b: &[i32] = &[];
/// assert!(b.is_empty());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
#[rustc_no_implicit_autorefs]
#[inline]
#[must_use]
pub const fn is_empty(&self) -> bool {
self.len() == 0
}
/// Returns the first element of the slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert_eq!(Some(&10), v.first());
///
/// let w: &[i32] = &[];
/// assert_eq!(None, w.first());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
#[inline]
#[must_use]
pub const fn first(&self) -> Option<&T> {
if let [first, ..] = self { Some(first) } else { None }
}
/// Returns a mutable reference to the first element of the slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(first) = x.first_mut() {
/// *first = 5;
/// }
/// assert_eq!(x, &[5, 1, 2]);
///
/// let y: &mut [i32] = &mut [];
/// assert_eq!(None, y.first_mut());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_first_last", since = "1.83.0")]
#[inline]
#[must_use]
pub const fn first_mut(&mut self) -> Option<&mut T> {
if let [first, ..] = self { Some(first) } else { None }
}
/// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let x = &[0, 1, 2];
///
/// if let Some((first, elements)) = x.split_first() {
/// assert_eq!(first, &0);
/// assert_eq!(elements, &[1, 2]);
/// }
/// ```
#[stable(feature = "slice_splits", since = "1.5.0")]
#[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
#[inline]
#[must_use]
pub const fn split_first(&self) -> Option<(&T, &[T])> {
if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
}
/// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some((first, elements)) = x.split_first_mut() {
/// *first = 3;
/// elements[0] = 4;
/// elements[1] = 5;
/// }
/// assert_eq!(x, &[3, 4, 5]);
/// ```
#[stable(feature = "slice_splits", since = "1.5.0")]
#[rustc_const_stable(feature = "const_slice_first_last", since = "1.83.0")]
#[inline]
#[must_use]
pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
}
/// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let x = &[0, 1, 2];
///
/// if let Some((last, elements)) = x.split_last() {
/// assert_eq!(last, &2);
/// assert_eq!(elements, &[0, 1]);
/// }
/// ```
#[stable(feature = "slice_splits", since = "1.5.0")]
#[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
#[inline]
#[must_use]
pub const fn split_last(&self) -> Option<(&T, &[T])> {
if let [init @ .., last] = self { Some((last, init)) } else { None }
}
/// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some((last, elements)) = x.split_last_mut() {
/// *last = 3;
/// elements[0] = 4;
/// elements[1] = 5;
/// }
/// assert_eq!(x, &[4, 5, 3]);
/// ```
#[stable(feature = "slice_splits", since = "1.5.0")]
#[rustc_const_stable(feature = "const_slice_first_last", since = "1.83.0")]
#[inline]
#[must_use]
pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
if let [init @ .., last] = self { Some((last, init)) } else { None }
}
/// Returns the last element of the slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert_eq!(Some(&30), v.last());
///
/// let w: &[i32] = &[];
/// assert_eq!(None, w.last());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
#[inline]
#[must_use]
pub const fn last(&self) -> Option<&T> {
if let [.., last] = self { Some(last) } else { None }
}
/// Returns a mutable reference to the last item in the slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(last) = x.last_mut() {
/// *last = 10;
/// }
/// assert_eq!(x, &[0, 1, 10]);
///
/// let y: &mut [i32] = &mut [];
/// assert_eq!(None, y.last_mut());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_first_last", since = "1.83.0")]
#[inline]
#[must_use]
pub const fn last_mut(&mut self) -> Option<&mut T> {
if let [.., last] = self { Some(last) } else { None }
}
/// Returns an array reference to the first `N` items in the slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let u = [10, 40, 30];
/// assert_eq!(Some(&[10, 40]), u.first_chunk::<2>());
///
/// let v: &[i32] = &[10];
/// assert_eq!(None, v.first_chunk::<2>());
///
/// let w: &[i32] = &[];
/// assert_eq!(Some(&[]), w.first_chunk::<0>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
pub const fn first_chunk<const N: usize>(&self) -> Option<&[T; N]> {
if self.len() < N {
None
} else {
// SAFETY: We explicitly check for the correct number of elements,
// and do not let the reference outlive the slice.
Some(unsafe { &*(self.as_ptr().cast_array()) })
}
}
/// Returns a mutable array reference to the first `N` items in the slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(first) = x.first_chunk_mut::<2>() {
/// first[0] = 5;
/// first[1] = 4;
/// }
/// assert_eq!(x, &[5, 4, 2]);
///
/// assert_eq!(None, x.first_chunk_mut::<4>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_stable(feature = "const_slice_first_last_chunk", since = "1.83.0")]
pub const fn first_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]> {
if self.len() < N {
None
} else {
// SAFETY: We explicitly check for the correct number of elements,
// do not let the reference outlive the slice,
// and require exclusive access to the entire slice to mutate the chunk.
Some(unsafe { &mut *(self.as_mut_ptr().cast_array()) })
}
}
/// Returns an array reference to the first `N` items in the slice and the remaining slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let x = &[0, 1, 2];
///
/// if let Some((first, elements)) = x.split_first_chunk::<2>() {
/// assert_eq!(first, &[0, 1]);
/// assert_eq!(elements, &[2]);
/// }
///
/// assert_eq!(None, x.split_first_chunk::<4>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
pub const fn split_first_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])> {
let Some((first, tail)) = self.split_at_checked(N) else { return None };
// SAFETY: We explicitly check for the correct number of elements,
// and do not let the references outlive the slice.
Some((unsafe { &*(first.as_ptr().cast_array()) }, tail))
}
/// Returns a mutable array reference to the first `N` items in the slice and the remaining
/// slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some((first, elements)) = x.split_first_chunk_mut::<2>() {
/// first[0] = 3;
/// first[1] = 4;
/// elements[0] = 5;
/// }
/// assert_eq!(x, &[3, 4, 5]);
///
/// assert_eq!(None, x.split_first_chunk_mut::<4>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_stable(feature = "const_slice_first_last_chunk", since = "1.83.0")]
pub const fn split_first_chunk_mut<const N: usize>(
&mut self,
) -> Option<(&mut [T; N], &mut [T])> {
let Some((first, tail)) = self.split_at_mut_checked(N) else { return None };
// SAFETY: We explicitly check for the correct number of elements,
// do not let the reference outlive the slice,
// and enforce exclusive mutability of the chunk by the split.
Some((unsafe { &mut *(first.as_mut_ptr().cast_array()) }, tail))
}
/// Returns an array reference to the last `N` items in the slice and the remaining slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let x = &[0, 1, 2];
///
/// if let Some((elements, last)) = x.split_last_chunk::<2>() {
/// assert_eq!(elements, &[0]);
/// assert_eq!(last, &[1, 2]);
/// }
///
/// assert_eq!(None, x.split_last_chunk::<4>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
pub const fn split_last_chunk<const N: usize>(&self) -> Option<(&[T], &[T; N])> {
let Some(index) = self.len().checked_sub(N) else { return None };
let (init, last) = self.split_at(index);
// SAFETY: We explicitly check for the correct number of elements,
// and do not let the references outlive the slice.
Some((init, unsafe { &*(last.as_ptr().cast_array()) }))
}
/// Returns a mutable array reference to the last `N` items in the slice and the remaining
/// slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some((elements, last)) = x.split_last_chunk_mut::<2>() {
/// last[0] = 3;
/// last[1] = 4;
/// elements[0] = 5;
/// }
/// assert_eq!(x, &[5, 3, 4]);
///
/// assert_eq!(None, x.split_last_chunk_mut::<4>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_stable(feature = "const_slice_first_last_chunk", since = "1.83.0")]
pub const fn split_last_chunk_mut<const N: usize>(
&mut self,
) -> Option<(&mut [T], &mut [T; N])> {
let Some(index) = self.len().checked_sub(N) else { return None };
let (init, last) = self.split_at_mut(index);
// SAFETY: We explicitly check for the correct number of elements,
// do not let the reference outlive the slice,
// and enforce exclusive mutability of the chunk by the split.
Some((init, unsafe { &mut *(last.as_mut_ptr().cast_array()) }))
}
/// Returns an array reference to the last `N` items in the slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let u = [10, 40, 30];
/// assert_eq!(Some(&[40, 30]), u.last_chunk::<2>());
///
/// let v: &[i32] = &[10];
/// assert_eq!(None, v.last_chunk::<2>());
///
/// let w: &[i32] = &[];
/// assert_eq!(Some(&[]), w.last_chunk::<0>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_stable(feature = "const_slice_last_chunk", since = "1.80.0")]
pub const fn last_chunk<const N: usize>(&self) -> Option<&[T; N]> {
// FIXME(const-hack): Without const traits, we need this instead of `get`.
let Some(index) = self.len().checked_sub(N) else { return None };
let (_, last) = self.split_at(index);
// SAFETY: We explicitly check for the correct number of elements,
// and do not let the references outlive the slice.
Some(unsafe { &*(last.as_ptr().cast_array()) })
}
/// Returns a mutable array reference to the last `N` items in the slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(last) = x.last_chunk_mut::<2>() {
/// last[0] = 10;
/// last[1] = 20;
/// }
/// assert_eq!(x, &[0, 10, 20]);
///
/// assert_eq!(None, x.last_chunk_mut::<4>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_stable(feature = "const_slice_first_last_chunk", since = "1.83.0")]
pub const fn last_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]> {
// FIXME(const-hack): Without const traits, we need this instead of `get`.
let Some(index) = self.len().checked_sub(N) else { return None };
let (_, last) = self.split_at_mut(index);
// SAFETY: We explicitly check for the correct number of elements,
// do not let the reference outlive the slice,
// and require exclusive access to the entire slice to mutate the chunk.
Some(unsafe { &mut *(last.as_mut_ptr().cast_array()) })
}
/// Returns a reference to an element or subslice depending on the type of
/// index.
///
/// - If given a position, returns a reference to the element at that
/// position or `None` if out of bounds.
/// - If given a range, returns the subslice corresponding to that range,
/// or `None` if out of bounds.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert_eq!(Some(&40), v.get(1));
/// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
/// assert_eq!(None, v.get(3));
/// assert_eq!(None, v.get(0..4));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_no_implicit_autorefs]
#[inline]
#[must_use]
#[rustc_const_unstable(feature = "const_index", issue = "143775")]
pub const fn get<I>(&self, index: I) -> Option<&I::Output>
where
I: [const] SliceIndex<Self>,
{
index.get(self)
}
/// Returns a mutable reference to an element or subslice depending on the
/// type of index (see [`get`]) or `None` if the index is out of bounds.
///
/// [`get`]: slice::get
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(elem) = x.get_mut(1) {
/// *elem = 42;
/// }
/// assert_eq!(x, &[0, 42, 2]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_no_implicit_autorefs]
#[inline]
#[must_use]
#[rustc_const_unstable(feature = "const_index", issue = "143775")]
#[rustc_no_writable]
pub const fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
where
I: [const] SliceIndex<Self>,
{
index.get_mut(self)
}
/// Returns a reference to an element or subslice, without doing bounds
/// checking.
///
/// For a safe alternative see [`get`].
///
/// # Safety
///
/// Calling this method with an out-of-bounds index is *[undefined behavior]*
/// even if the resulting reference is not used.
///
/// You can think of this like `.get(index).unwrap_unchecked()`. It's UB
/// to call `.get_unchecked(len)`, even if you immediately convert to a
/// pointer. And it's UB to call `.get_unchecked(..len + 1)`,
/// `.get_unchecked(..=len)`, or similar.
///
/// [`get`]: slice::get
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
///
/// # Examples
///
/// ```
/// let x = &[1, 2, 4];
///
/// unsafe {
/// assert_eq!(x.get_unchecked(1), &2);
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_no_implicit_autorefs]
#[inline]
#[must_use]
#[track_caller]
#[rustc_const_unstable(feature = "const_index", issue = "143775")]
pub const unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
where
I: [const] SliceIndex<Self>,
{
// SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
// the slice is dereferenceable because `self` is a safe reference.
// The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
unsafe { &*index.get_unchecked(self) }
}
/// Returns a mutable reference to an element or subslice, without doing
/// bounds checking.
///
/// For a safe alternative see [`get_mut`].
///
/// # Safety
///
/// Calling this method with an out-of-bounds index is *[undefined behavior]*
/// even if the resulting reference is not used.
///
/// You can think of this like `.get_mut(index).unwrap_unchecked()`. It's
/// UB to call `.get_unchecked_mut(len)`, even if you immediately convert
/// to a pointer. And it's UB to call `.get_unchecked_mut(..len + 1)`,
/// `.get_unchecked_mut(..=len)`, or similar.
///
/// [`get_mut`]: slice::get_mut
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
///
/// # Examples
///
/// ```
/// let x = &mut [1, 2, 4];
///
/// unsafe {
/// let elem = x.get_unchecked_mut(1);
/// *elem = 13;
/// }
/// assert_eq!(x, &[1, 13, 4]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_no_implicit_autorefs]
#[inline]
#[must_use]
#[track_caller]
#[rustc_const_unstable(feature = "const_index", issue = "143775")]
#[rustc_no_writable]
pub const unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
where
I: [const] SliceIndex<Self>,
{
// SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
// the slice is dereferenceable because `self` is a safe reference.
// The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
unsafe { &mut *index.get_unchecked_mut(self) }
}
/// Returns a raw pointer to the slice's buffer.
///
/// The caller must ensure that the slice outlives the pointer this
/// function returns, or else it will end up dangling.
///
/// The caller must also ensure that the memory the pointer (non-transitively) points to
/// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
/// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
///
/// Modifying the container referenced by this slice may cause its buffer
/// to be reallocated, which would also make any pointers to it invalid.
///
/// # Examples
///
/// ```
/// let x = &[1, 2, 4];
/// let x_ptr = x.as_ptr();
///
/// unsafe {
/// for i in 0..x.len() {
/// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
/// }
/// }
/// ```
///
/// [`as_mut_ptr`]: slice::as_mut_ptr
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
#[rustc_never_returns_null_ptr]
#[rustc_as_ptr]
#[inline(always)]
#[must_use]
pub const fn as_ptr(&self) -> *const T {
self as *const [T] as *const T
}
/// Returns an unsafe mutable pointer to the slice's buffer.
///
/// The caller must ensure that the slice outlives the pointer this
/// function returns, or else it will end up dangling.
///
/// Modifying the container referenced by this slice may cause its buffer
/// to be reallocated, which would also make any pointers to it invalid.
///
/// # Examples
///
/// ```
/// let x = &mut [1, 2, 4];
/// let x_ptr = x.as_mut_ptr();
///
/// unsafe {
/// for i in 0..x.len() {
/// *x_ptr.add(i) += 2;
/// }
/// }
/// assert_eq!(x, &[3, 4, 6]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
#[rustc_never_returns_null_ptr]
#[rustc_as_ptr]
#[inline(always)]
#[must_use]
#[rustc_no_writable]
pub const fn as_mut_ptr(&mut self) -> *mut T {
self as *mut [T] as *mut T
}
/// Returns the two raw pointers spanning the slice.
///
/// The returned range is half-open, which means that the end pointer
/// points *one past* the last element of the slice. This way, an empty
/// slice is represented by two equal pointers, and the difference between
/// the two pointers represents the size of the slice.
///
/// See [`as_ptr`] for warnings on using these pointers. The end pointer
/// requires extra caution, as it does not point to a valid element in the
/// slice.
///
/// This function is useful for interacting with foreign interfaces which
/// use two pointers to refer to a range of elements in memory, as is
/// common in C++.
///
/// It can also be useful to check if a pointer to an element refers to an
/// element of this slice:
///
/// ```
/// let a = [1, 2, 3];
/// let x = &a[1] as *const _;
/// let y = &5 as *const _;
///
/// assert!(a.as_ptr_range().contains(&x));
/// assert!(!a.as_ptr_range().contains(&y));
/// ```
///
/// [`as_ptr`]: slice::as_ptr
#[stable(feature = "slice_ptr_range", since = "1.48.0")]
#[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
#[inline]
#[must_use]
pub const fn as_ptr_range(&self) -> Range<*const T> {
let start = self.as_ptr();
// SAFETY: The `add` here is safe, because:
//
// - Both pointers are part of the same object, as pointing directly
// past the object also counts.
//
// - The size of the slice is never larger than `isize::MAX` bytes, as
// noted here:
// - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
// - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
// - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
// (This doesn't seem normative yet, but the very same assumption is
// made in many places, including the Index implementation of slices.)
//
// - There is no wrapping around involved, as slices do not wrap past
// the end of the address space.
//
// See the documentation of [`pointer::add`].
let end = unsafe { start.add(self.len()) };
start..end
}
/// Returns the two unsafe mutable pointers spanning the slice.
///
/// The returned range is half-open, which means that the end pointer
/// points *one past* the last element of the slice. This way, an empty
/// slice is represented by two equal pointers, and the difference between
/// the two pointers represents the size of the slice.
///
/// See [`as_mut_ptr`] for warnings on using these pointers. The end
/// pointer requires extra caution, as it does not point to a valid element
/// in the slice.
///
/// This function is useful for interacting with foreign interfaces which
/// use two pointers to refer to a range of elements in memory, as is
/// common in C++.
///
/// [`as_mut_ptr`]: slice::as_mut_ptr
#[stable(feature = "slice_ptr_range", since = "1.48.0")]
#[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
#[inline]
#[must_use]
pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
let start = self.as_mut_ptr();
// SAFETY: See as_ptr_range() above for why `add` here is safe.
let end = unsafe { start.add(self.len()) };
start..end
}
/// Gets a reference to the underlying array.
///
/// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
#[stable(feature = "core_slice_as_array", since = "1.93.0")]
#[rustc_const_stable(feature = "core_slice_as_array", since = "1.93.0")]
#[inline]
#[must_use]
pub const fn as_array<const N: usize>(&self) -> Option<&[T; N]> {
if self.len() == N {
let ptr = self.as_ptr().cast_array();
// SAFETY: The underlying array of a slice can be reinterpreted as an actual array `[T; N]` if `N` is not greater than the slice's length.
let me = unsafe { &*ptr };
Some(me)
} else {
None
}
}
/// Gets a mutable reference to the slice's underlying array.
///
/// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
#[stable(feature = "core_slice_as_array", since = "1.93.0")]
#[rustc_const_stable(feature = "core_slice_as_array", since = "1.93.0")]
#[inline]
#[must_use]
pub const fn as_mut_array<const N: usize>(&mut self) -> Option<&mut [T; N]> {
if self.len() == N {
let ptr = self.as_mut_ptr().cast_array();
// SAFETY: The underlying array of a slice can be reinterpreted as an actual array `[T; N]` if `N` is not greater than the slice's length.
let me = unsafe { &mut *ptr };
Some(me)
} else {
None
}
}
/// Swaps two elements in the slice.
///
/// If `a` equals to `b`, it's guaranteed that elements won't change value.
///
/// # Arguments
///
/// * a - The index of the first element
/// * b - The index of the second element
///
/// # Panics
///
/// Panics if `a` or `b` are out of bounds.
///
/// # Examples
///
/// ```
/// let mut v = ["a", "b", "c", "d", "e"];
/// v.swap(2, 4);
/// assert!(v == ["a", "b", "e", "d", "c"]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_swap", since = "1.85.0")]
#[inline]
#[track_caller]
pub const fn swap(&mut self, a: usize, b: usize) {
// Bounds checks that panic exactly like indexing would.
let _ = &self[a];
let _ = &self[b];
// SAFETY: `a` and `b` were checked to be in bounds above.
unsafe {
self.swap_unchecked(a, b);
}
}
/// Swaps two elements in the slice, without doing bounds checking.
///
/// For a safe alternative see [`swap`].
///
/// # Arguments
///
/// * a - The index of the first element
/// * b - The index of the second element
///
/// # Safety
///
/// Calling this method with an out-of-bounds index is *[undefined behavior]*.
/// The caller has to ensure that `a < self.len()` and `b < self.len()`.
///
/// # Examples
///
/// ```
/// #![feature(slice_swap_unchecked)]
///
/// let mut v = ["a", "b", "c", "d"];
/// // SAFETY: we know that 1 and 3 are both indices of the slice
/// unsafe { v.swap_unchecked(1, 3) };
/// assert!(v == ["a", "d", "c", "b"]);
/// ```
///
/// [`swap`]: slice::swap
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
#[unstable(feature = "slice_swap_unchecked", issue = "88539")]
#[track_caller]
pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
assert_unsafe_precondition!(
check_library_ub,
"slice::swap_unchecked requires that the indices are within the slice",
(
len: usize = self.len(),
a: usize = a,
b: usize = b,
) => a < len && b < len,
);
let ptr = self.as_mut_ptr();
// SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
unsafe {
ptr::swap(ptr.add(a), ptr.add(b));
}
}
/// Reverses the order of elements in the slice, in place.
///
/// # Examples
///
/// ```
/// let mut v = [1, 2, 3];
/// v.reverse();
/// assert!(v == [3, 2, 1]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_reverse", since = "1.90.0")]
#[inline]
pub const fn reverse(&mut self) {
let half_len = self.len() / 2;
let Range { start, end } = self.as_mut_ptr_range();
// These slices will skip the middle item for an odd length,
// since that one doesn't need to move.
let (front_half, back_half) =
// SAFETY: Both are subparts of the original slice, so the memory
// range is valid, and they don't overlap because they're each only
// half (or less) of the original slice.
unsafe {
(
slice::from_raw_parts_mut(start, half_len),
slice::from_raw_parts_mut(end.sub(half_len), half_len),
)
};
// Introducing a function boundary here means that the two halves
// get `noalias` markers, allowing better optimization as LLVM
// knows that they're disjoint, unlike in the original slice.
revswap(front_half, back_half, half_len);
#[inline]
const fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) {
debug_assert!(a.len() == n);
debug_assert!(b.len() == n);
// Because this function is first compiled in isolation,
// this check tells LLVM that the indexing below is
// in-bounds. Then after inlining -- once the actual
// lengths of the slices are known -- it's removed.
// FIXME(const_trait_impl) replace with let (a, b) = (&mut a[..n], &mut b[..n]);
let (a, _) = a.split_at_mut(n);
let (b, _) = b.split_at_mut(n);
let mut i = 0;
while i < n {
mem::swap(&mut a[i], &mut b[n - 1 - i]);
i += 1;
}
}
}
/// Returns an iterator over the slice.
///
/// The iterator yields all items from start to end.
///
/// # Examples
///
/// ```
/// let x = &[1, 2, 4];
/// let mut iterator = x.iter();
///
/// assert_eq!(iterator.next(), Some(&1));
/// assert_eq!(iterator.next(), Some(&2));
/// assert_eq!(iterator.next(), Some(&4));
/// assert_eq!(iterator.next(), None);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
#[rustc_diagnostic_item = "slice_iter"]
pub const fn iter(&self) -> Iter<'_, T> {
Iter::new(self)
}
/// Returns an iterator that allows modifying each value.
///
/// The iterator yields all items from start to end.
///
/// # Examples
///
/// ```
/// let x = &mut [1, 2, 4];
/// for elem in x.iter_mut() {
/// *elem += 2;
/// }
/// assert_eq!(x, &[3, 4, 6]);
/// ```
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub const fn iter_mut(&mut self) -> IterMut<'_, T> {
IterMut::new(self)
}
/// Returns an iterator over all contiguous windows of length
/// `size`. The windows overlap. If the slice is shorter than
/// `size`, the iterator returns no values.
///
/// # Panics
///
/// Panics if `size` is zero.
///
/// # Examples
///
/// ```
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let mut iter = slice.windows(3);
/// assert_eq!(iter.next().unwrap(), &['l', 'o', 'r']);
/// assert_eq!(iter.next().unwrap(), &['o', 'r', 'e']);
/// assert_eq!(iter.next().unwrap(), &['r', 'e', 'm']);
/// assert!(iter.next().is_none());
/// ```
///
/// If the slice is shorter than `size`:
///
/// ```
/// let slice = ['f', 'o', 'o'];
/// let mut iter = slice.windows(4);
/// assert!(iter.next().is_none());
/// ```
///
/// Because the [Iterator] trait cannot represent the required lifetimes,
/// there is no `windows_mut` analog to `windows`;
/// `[0,1,2].windows_mut(2).collect()` would violate [the rules of references]
/// (though a [LendingIterator] analog is possible). You can sometimes use
/// [`Cell::as_slice_of_cells`](crate::cell::Cell::as_slice_of_cells) in
/// conjunction with `windows` instead:
///
/// [the rules of references]: https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html#the-rules-of-references
/// [LendingIterator]: https://blog.rust-lang.org/2022/10/28/gats-stabilization.html
/// ```
/// use std::cell::Cell;
///
/// let mut array = ['R', 'u', 's', 't', ' ', '2', '0', '1', '5'];
/// let slice = &mut array[..];
/// let slice_of_cells: &[Cell<char>] = Cell::from_mut(slice).as_slice_of_cells();
/// for w in slice_of_cells.windows(3) {
/// Cell::swap(&w[0], &w[2]);
/// }
/// assert_eq!(array, ['s', 't', ' ', '2', '0', '1', '5', 'u', 'R']);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
#[track_caller]
pub const fn windows(&self, size: usize) -> Windows<'_, T> {
let size = NonZero::new(size).expect("window size must be non-zero");
Windows::new(self, size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
/// beginning of the slice.
///
/// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
/// slice, then the last chunk will not have length `chunk_size`.
///
/// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
/// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
/// slice.
///
/// If your `chunk_size` is a constant, consider using [`as_chunks`] instead, which will
/// give references to arrays of exactly that length, rather than slices.
///
/// # Panics
///
/// Panics if `chunk_size` is zero.
///
/// # Examples
///
/// ```
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let mut iter = slice.chunks(2);
/// assert_eq!(iter.next().unwrap(), &['l', 'o']);
/// assert_eq!(iter.next().unwrap(), &['r', 'e']);
/// assert_eq!(iter.next().unwrap(), &['m']);
/// assert!(iter.next().is_none());
/// ```
///
/// [`chunks_exact`]: slice::chunks_exact
/// [`rchunks`]: slice::rchunks
/// [`as_chunks`]: slice::as_chunks
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
#[track_caller]
pub const fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
Chunks::new(self, chunk_size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
/// beginning of the slice.
///
/// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
/// length of the slice, then the last chunk will not have length `chunk_size`.
///
/// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
/// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
/// the end of the slice.
///
/// If your `chunk_size` is a constant, consider using [`as_chunks_mut`] instead, which will
/// give references to arrays of exactly that length, rather than slices.
///
/// # Panics
///
/// Panics if `chunk_size` is zero.
///
/// # Examples
///
/// ```
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// for chunk in v.chunks_mut(2) {
/// for elem in chunk.iter_mut() {
/// *elem += count;
/// }
/// count += 1;
/// }
/// assert_eq!(v, &[1, 1, 2, 2, 3]);
/// ```
///
/// [`chunks_exact_mut`]: slice::chunks_exact_mut
/// [`rchunks_mut`]: slice::rchunks_mut
/// [`as_chunks_mut`]: slice::as_chunks_mut
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
#[track_caller]
pub const fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
ChunksMut::new(self, chunk_size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
/// beginning of the slice.
///
/// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
/// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
/// from the `remainder` function of the iterator.
///
/// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
/// resulting code better than in the case of [`chunks`].
///
/// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
/// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
///
/// If your `chunk_size` is a constant, consider using [`as_chunks`] instead, which will
/// give references to arrays of exactly that length, rather than slices.
///
/// # Panics
///
/// Panics if `chunk_size` is zero.
///
/// # Examples
///
/// ```
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let mut iter = slice.chunks_exact(2);
/// assert_eq!(iter.next().unwrap(), &['l', 'o']);
/// assert_eq!(iter.next().unwrap(), &['r', 'e']);
/// assert!(iter.next().is_none());
/// assert_eq!(iter.remainder(), &['m']);
/// ```
///
/// [`chunks`]: slice::chunks
/// [`rchunks_exact`]: slice::rchunks_exact
/// [`as_chunks`]: slice::as_chunks
#[stable(feature = "chunks_exact", since = "1.31.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
#[track_caller]
pub const fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
ChunksExact::new(self, chunk_size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
/// beginning of the slice.
///
/// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
/// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
/// retrieved from the `into_remainder` function of the iterator.
///
/// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
/// resulting code better than in the case of [`chunks_mut`].
///
/// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
/// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
/// the slice.
///
/// If your `chunk_size` is a constant, consider using [`as_chunks_mut`] instead, which will
/// give references to arrays of exactly that length, rather than slices.
///
/// # Panics
///
/// Panics if `chunk_size` is zero.
///
/// # Examples
///
/// ```
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// for chunk in v.chunks_exact_mut(2) {
/// for elem in chunk.iter_mut() {
/// *elem += count;
/// }
/// count += 1;
/// }
/// assert_eq!(v, &[1, 1, 2, 2, 0]);
/// ```
///
/// [`chunks_mut`]: slice::chunks_mut
/// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
/// [`as_chunks_mut`]: slice::as_chunks_mut
#[stable(feature = "chunks_exact", since = "1.31.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
#[track_caller]
pub const fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
ChunksExactMut::new(self, chunk_size)
}
/// Splits the slice into a slice of `N`-element arrays,
/// assuming that there's no remainder.
///
/// This is the inverse operation to [`as_flattened`].
///
/// [`as_flattened`]: slice::as_flattened
///
/// As this is `unsafe`, consider whether you could use [`as_chunks`] or
/// [`as_rchunks`] instead, perhaps via something like
/// `if let (chunks, []) = slice.as_chunks()` or
/// `let (chunks, []) = slice.as_chunks() else { unreachable!() };`.
///
/// [`as_chunks`]: slice::as_chunks
/// [`as_rchunks`]: slice::as_rchunks
///
/// # Safety
///
/// This may only be called when
/// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
/// - `N != 0`.
///
/// # Examples
///
/// ```
/// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
/// let chunks: &[[char; 1]] =
/// // SAFETY: 1-element chunks never have remainder
/// unsafe { slice.as_chunks_unchecked() };
/// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
/// let chunks: &[[char; 3]] =
/// // SAFETY: The slice length (6) is a multiple of 3
/// unsafe { slice.as_chunks_unchecked() };
/// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
///
/// // These would be unsound:
/// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
/// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
/// ```
#[stable(feature = "slice_as_chunks", since = "1.88.0")]
#[rustc_const_stable(feature = "slice_as_chunks", since = "1.88.0")]
#[inline]
#[must_use]
#[track_caller]
pub const unsafe fn as_chunks_unchecked<#[rustc_panics_when_zero] const N: usize>(
&self,
) -> &[[T; N]] {
assert_unsafe_precondition!(
check_language_ub,
"slice::as_chunks_unchecked requires `N != 0` and the slice to split exactly into `N`-element chunks",
(n: usize = N, len: usize = self.len()) => n != 0 && len.is_multiple_of(n),
);
// SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
let new_len = unsafe { exact_div(self.len(), N) };
// SAFETY: We cast a slice of `new_len * N` elements into
// a slice of `new_len` many `N` elements chunks.
unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
}
/// Splits the slice into a slice of `N`-element arrays,
/// starting at the beginning of the slice,
/// and a remainder slice with length strictly less than `N`.
///
/// The remainder is meaningful in the division sense. Given
/// `let (chunks, remainder) = slice.as_chunks()`, then:
/// - `chunks.len()` equals `slice.len() / N`,
/// - `remainder.len()` equals `slice.len() % N`, and
/// - `slice.len()` equals `chunks.len() * N + remainder.len()`.
///
/// You can flatten the chunks back into a slice-of-`T` with [`as_flattened`].
///
/// [`as_flattened`]: slice::as_flattened
///
/// # Panics
///
/// Panics if `N` is zero.
///
/// Note that this check is against a const generic parameter, not a runtime
/// value, and thus a particular monomorphization will either always panic
/// or it will never panic.
///
/// # Examples
///
/// ```
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let (chunks, remainder) = slice.as_chunks();
/// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
/// assert_eq!(remainder, &['m']);
/// ```
///
/// If you expect the slice to be an exact multiple, you can combine
/// `let`-`else` with an empty slice pattern:
/// ```
/// let slice = ['R', 'u', 's', 't'];
/// let (chunks, []) = slice.as_chunks::<2>() else {
/// panic!("slice didn't have even length")
/// };
/// assert_eq!(chunks, &[['R', 'u'], ['s', 't']]);
/// ```
#[stable(feature = "slice_as_chunks", since = "1.88.0")]
#[rustc_const_stable(feature = "slice_as_chunks", since = "1.88.0")]
#[inline]
#[track_caller]
#[must_use]
pub const fn as_chunks<#[rustc_panics_when_zero] const N: usize>(&self) -> (&[[T; N]], &[T]) {
assert!(N != 0, "chunk size must be non-zero");
let len_rounded_down = self.len() / N * N;
// SAFETY: The rounded-down value is always the same or smaller than the
// original length, and thus must be in-bounds of the slice.
let (multiple_of_n, remainder) = unsafe { self.split_at_unchecked(len_rounded_down) };
// SAFETY: We already panicked for zero, and ensured by construction
// that the length of the subslice is a multiple of N.
let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
(array_slice, remainder)
}
/// Splits the slice into a slice of `N`-element arrays,
/// starting at the end of the slice,
/// and a remainder slice with length strictly less than `N`.
///
/// The remainder is meaningful in the division sense. Given
/// `let (remainder, chunks) = slice.as_rchunks()`, then:
/// - `remainder.len()` equals `slice.len() % N`,
/// - `chunks.len()` equals `slice.len() / N`, and
/// - `slice.len()` equals `chunks.len() * N + remainder.len()`.
///
/// You can flatten the chunks back into a slice-of-`T` with [`as_flattened`].
///
/// [`as_flattened`]: slice::as_flattened
///
/// # Panics
///
/// Panics if `N` is zero.
///
/// Note that this check is against a const generic parameter, not a runtime
/// value, and thus a particular monomorphization will either always panic
/// or it will never panic.
///
/// # Examples
///
/// ```
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let (remainder, chunks) = slice.as_rchunks();
/// assert_eq!(remainder, &['l']);
/// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
/// ```
#[stable(feature = "slice_as_chunks", since = "1.88.0")]
#[rustc_const_stable(feature = "slice_as_chunks", since = "1.88.0")]
#[inline]
#[track_caller]
#[must_use]
pub const fn as_rchunks<#[rustc_panics_when_zero] const N: usize>(&self) -> (&[T], &[[T; N]]) {
assert!(N != 0, "chunk size must be non-zero");
let len = self.len() / N;
let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
// SAFETY: We already panicked for zero, and ensured by construction
// that the length of the subslice is a multiple of N.
let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
(remainder, array_slice)
}
/// Splits the slice into a slice of `N`-element arrays,
/// assuming that there's no remainder.
///
/// This is the inverse operation to [`as_flattened_mut`].
///
/// [`as_flattened_mut`]: slice::as_flattened_mut
///
/// As this is `unsafe`, consider whether you could use [`as_chunks_mut`] or
/// [`as_rchunks_mut`] instead, perhaps via something like
/// `if let (chunks, []) = slice.as_chunks_mut()` or
/// `let (chunks, []) = slice.as_chunks_mut() else { unreachable!() };`.
///
/// [`as_chunks_mut`]: slice::as_chunks_mut
/// [`as_rchunks_mut`]: slice::as_rchunks_mut
///
/// # Safety
///
/// This may only be called when
/// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
/// - `N != 0`.
///
/// # Examples
///
/// ```
/// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
/// let chunks: &mut [[char; 1]] =
/// // SAFETY: 1-element chunks never have remainder
/// unsafe { slice.as_chunks_unchecked_mut() };
/// chunks[0] = ['L'];
/// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
/// let chunks: &mut [[char; 3]] =
/// // SAFETY: The slice length (6) is a multiple of 3
/// unsafe { slice.as_chunks_unchecked_mut() };
/// chunks[1] = ['a', 'x', '?'];
/// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
///
/// // These would be unsound:
/// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
/// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
/// ```
#[stable(feature = "slice_as_chunks", since = "1.88.0")]
#[rustc_const_stable(feature = "slice_as_chunks", since = "1.88.0")]
#[inline]
#[must_use]
#[track_caller]
pub const unsafe fn as_chunks_unchecked_mut<#[rustc_panics_when_zero] const N: usize>(
&mut self,
) -> &mut [[T; N]] {
assert_unsafe_precondition!(
check_language_ub,
"slice::as_chunks_unchecked requires `N != 0` and the slice to split exactly into `N`-element chunks",
(n: usize = N, len: usize = self.len()) => n != 0 && len.is_multiple_of(n)
);
// SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
let new_len = unsafe { exact_div(self.len(), N) };
// SAFETY: We cast a slice of `new_len * N` elements into
// a slice of `new_len` many `N` elements chunks.
unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
}
/// Splits the slice into a slice of `N`-element arrays,
/// starting at the beginning of the slice,
/// and a remainder slice with length strictly less than `N`.
///
/// The remainder is meaningful in the division sense. Given
/// `let (chunks, remainder) = slice.as_chunks_mut()`, then:
/// - `chunks.len()` equals `slice.len() / N`,
/// - `remainder.len()` equals `slice.len() % N`, and
/// - `slice.len()` equals `chunks.len() * N + remainder.len()`.
///
/// You can flatten the chunks back into a slice-of-`T` with [`as_flattened_mut`].
///
/// [`as_flattened_mut`]: slice::as_flattened_mut
///
/// # Panics
///
/// Panics if `N` is zero.
///
/// Note that this check is against a const generic parameter, not a runtime
/// value, and thus a particular monomorphization will either always panic
/// or it will never panic.
///
/// # Examples
///
/// ```
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// let (chunks, remainder) = v.as_chunks_mut();
/// remainder[0] = 9;
/// for chunk in chunks {
/// *chunk = [count; 2];
/// count += 1;
/// }
/// assert_eq!(v, &[1, 1, 2, 2, 9]);
/// ```
#[stable(feature = "slice_as_chunks", since = "1.88.0")]
#[rustc_const_stable(feature = "slice_as_chunks", since = "1.88.0")]
#[inline]
#[track_caller]
#[must_use]
pub const fn as_chunks_mut<#[rustc_panics_when_zero] const N: usize>(
&mut self,
) -> (&mut [[T; N]], &mut [T]) {
assert!(N != 0, "chunk size must be non-zero");
let len_rounded_down = self.len() / N * N;
// SAFETY: The rounded-down value is always the same or smaller than the
// original length, and thus must be in-bounds of the slice.
let (multiple_of_n, remainder) = unsafe { self.split_at_mut_unchecked(len_rounded_down) };
// SAFETY: We already panicked for zero, and ensured by construction
// that the length of the subslice is a multiple of N.
let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
(array_slice, remainder)
}
/// Splits the slice into a slice of `N`-element arrays,
/// starting at the end of the slice,
/// and a remainder slice with length strictly less than `N`.
///
/// The remainder is meaningful in the division sense. Given
/// `let (remainder, chunks) = slice.as_rchunks_mut()`, then:
/// - `remainder.len()` equals `slice.len() % N`,
/// - `chunks.len()` equals `slice.len() / N`, and
/// - `slice.len()` equals `chunks.len() * N + remainder.len()`.
///
/// You can flatten the chunks back into a slice-of-`T` with [`as_flattened_mut`].
///
/// [`as_flattened_mut`]: slice::as_flattened_mut
///
/// # Panics
///
/// Panics if `N` is zero.
///
/// Note that this check is against a const generic parameter, not a runtime
/// value, and thus a particular monomorphization will either always panic
/// or it will never panic.
///
/// # Examples
///
/// ```
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// let (remainder, chunks) = v.as_rchunks_mut();
/// remainder[0] = 9;
/// for chunk in chunks {
/// *chunk = [count; 2];
/// count += 1;
/// }
/// assert_eq!(v, &[9, 1, 1, 2, 2]);
/// ```
#[stable(feature = "slice_as_chunks", since = "1.88.0")]
#[rustc_const_stable(feature = "slice_as_chunks", since = "1.88.0")]
#[inline]
#[track_caller]
#[must_use]
pub const fn as_rchunks_mut<#[rustc_panics_when_zero] const N: usize>(
&mut self,
) -> (&mut [T], &mut [[T; N]]) {
assert!(N != 0, "chunk size must be non-zero");
let len = self.len() / N;
let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
// SAFETY: We already panicked for zero, and ensured by construction
// that the length of the subslice is a multiple of N.
let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
(remainder, array_slice)
}
/// Returns an iterator over overlapping windows of `N` elements of a slice,
/// starting at the beginning of the slice.
///
/// This is the const generic equivalent of [`windows`].
///
/// If `N` is greater than the size of the slice, it will return no windows.
///
/// # Panics
///
/// Panics if `N` is zero.
///
/// Note that this check is against a const generic parameter, not a runtime
/// value, and thus a particular monomorphization will either always panic
/// or it will never panic.
///
/// # Examples
///
/// ```
/// let slice = [0, 1, 2, 3];
/// let mut iter = slice.array_windows();
/// assert_eq!(iter.next().unwrap(), &[0, 1]);
/// assert_eq!(iter.next().unwrap(), &[1, 2]);
/// assert_eq!(iter.next().unwrap(), &[2, 3]);
/// assert!(iter.next().is_none());
/// ```
///
/// [`windows`]: slice::windows
#[stable(feature = "array_windows", since = "1.94.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
#[track_caller]
pub const fn array_windows<#[rustc_panics_when_zero] const N: usize>(
&self,
) -> ArrayWindows<'_, T, N> {
assert!(N != 0, "window size must be non-zero");
ArrayWindows::new(self)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
/// of the slice.
///
/// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
/// slice, then the last chunk will not have length `chunk_size`.
///
/// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
/// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
/// of the slice.
///
/// If your `chunk_size` is a constant, consider using [`as_rchunks`] instead, which will
/// give references to arrays of exactly that length, rather than slices.
///
/// # Panics
///
/// Panics if `chunk_size` is zero.
///
/// # Examples
///
/// ```
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let mut iter = slice.rchunks(2);
/// assert_eq!(iter.next().unwrap(), &['e', 'm']);
/// assert_eq!(iter.next().unwrap(), &['o', 'r']);
/// assert_eq!(iter.next().unwrap(), &['l']);
/// assert!(iter.next().is_none());
/// ```
///
/// [`rchunks_exact`]: slice::rchunks_exact
/// [`chunks`]: slice::chunks
/// [`as_rchunks`]: slice::as_rchunks
#[stable(feature = "rchunks", since = "1.31.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
#[track_caller]
pub const fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
RChunks::new(self, chunk_size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
/// of the slice.
///
/// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
/// length of the slice, then the last chunk will not have length `chunk_size`.
///
/// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
/// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
/// beginning of the slice.
///
/// If your `chunk_size` is a constant, consider using [`as_rchunks_mut`] instead, which will
/// give references to arrays of exactly that length, rather than slices.
///
/// # Panics
///
/// Panics if `chunk_size` is zero.
///
/// # Examples
///
/// ```
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// for chunk in v.rchunks_mut(2) {
/// for elem in chunk.iter_mut() {
/// *elem += count;
/// }
/// count += 1;
/// }
/// assert_eq!(v, &[3, 2, 2, 1, 1]);
/// ```
///
/// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
/// [`chunks_mut`]: slice::chunks_mut
/// [`as_rchunks_mut`]: slice::as_rchunks_mut
#[stable(feature = "rchunks", since = "1.31.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
#[track_caller]
pub const fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
RChunksMut::new(self, chunk_size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
/// end of the slice.
///
/// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
/// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
/// from the `remainder` function of the iterator.
///
/// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
/// resulting code better than in the case of [`rchunks`].
///
/// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
/// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
/// slice.
///
/// If your `chunk_size` is a constant, consider using [`as_rchunks`] instead, which will
/// give references to arrays of exactly that length, rather than slices.
///
/// # Panics
///
/// Panics if `chunk_size` is zero.
///
/// # Examples
///
/// ```
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let mut iter = slice.rchunks_exact(2);
/// assert_eq!(iter.next().unwrap(), &['e', 'm']);
/// assert_eq!(iter.next().unwrap(), &['o', 'r']);
/// assert!(iter.next().is_none());
/// assert_eq!(iter.remainder(), &['l']);
/// ```
///
/// [`chunks`]: slice::chunks
/// [`rchunks`]: slice::rchunks
/// [`chunks_exact`]: slice::chunks_exact
/// [`as_rchunks`]: slice::as_rchunks
#[stable(feature = "rchunks", since = "1.31.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
#[track_caller]
pub const fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
RChunksExact::new(self, chunk_size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
/// of the slice.
///
/// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
/// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
/// retrieved from the `into_remainder` function of the iterator.
///
/// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
/// resulting code better than in the case of [`chunks_mut`].
///
/// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
/// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
/// of the slice.
///
/// If your `chunk_size` is a constant, consider using [`as_rchunks_mut`] instead, which will
/// give references to arrays of exactly that length, rather than slices.
///
/// # Panics
///
/// Panics if `chunk_size` is zero.
///
/// # Examples
///
/// ```
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// for chunk in v.rchunks_exact_mut(2) {
/// for elem in chunk.iter_mut() {
/// *elem += count;
/// }
/// count += 1;
/// }
/// assert_eq!(v, &[0, 2, 2, 1, 1]);
/// ```
///
/// [`chunks_mut`]: slice::chunks_mut
/// [`rchunks_mut`]: slice::rchunks_mut
/// [`chunks_exact_mut`]: slice::chunks_exact_mut
/// [`as_rchunks_mut`]: slice::as_rchunks_mut
#[stable(feature = "rchunks", since = "1.31.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
#[track_caller]
pub const fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
RChunksExactMut::new(self, chunk_size)
}
/// Returns an iterator over the slice producing non-overlapping runs
/// of elements using the predicate to separate them.
///
/// The predicate is called for every pair of consecutive elements,
/// meaning that it is called on `slice[0]` and `slice[1]`,
/// followed by `slice[1]` and `slice[2]`, and so on.
///
/// # Examples
///
/// ```
/// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
///
/// let mut iter = slice.chunk_by(|a, b| a == b);
///
/// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
/// assert_eq!(iter.next(), Some(&[3, 3][..]));
/// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
/// assert_eq!(iter.next(), None);
/// ```
///
/// This method can be used to extract the sorted subslices:
///
/// ```
/// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
///
/// let mut iter = slice.chunk_by(|a, b| a <= b);
///
/// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
/// assert_eq!(iter.next(), Some(&[2, 3][..]));
/// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
/// assert_eq!(iter.next(), None);
/// ```
#[stable(feature = "slice_group_by", since = "1.77.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
pub const fn chunk_by<F>(&self, pred: F) -> ChunkBy<'_, T, F>
where
F: FnMut(&T, &T) -> bool,
{
ChunkBy::new(self, pred)
}
/// Returns an iterator over the slice producing non-overlapping mutable
/// runs of elements using the predicate to separate them.
///
/// The predicate is called for every pair of consecutive elements,
/// meaning that it is called on `slice[0]` and `slice[1]`,
/// followed by `slice[1]` and `slice[2]`, and so on.
///
/// # Examples
///
/// ```
/// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
///
/// let mut iter = slice.chunk_by_mut(|a, b| a == b);
///
/// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
/// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
/// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
/// assert_eq!(iter.next(), None);
/// ```
///
/// This method can be used to extract the sorted subslices:
///
/// ```
/// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
///
/// let mut iter = slice.chunk_by_mut(|a, b| a <= b);
///
/// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
/// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
/// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
/// assert_eq!(iter.next(), None);
/// ```
#[stable(feature = "slice_group_by", since = "1.77.0")]
#[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
#[inline]
pub const fn chunk_by_mut<F>(&mut self, pred: F) -> ChunkByMut<'_, T, F>
where
F: FnMut(&T, &T) -> bool,
{
ChunkByMut::new(self, pred)
}
/// Divides one slice into two at an index.
///
/// The first will contain all indices from `[0, mid)` (excluding
/// the index `mid` itself) and the second will contain all
/// indices from `[mid, len)` (excluding the index `len` itself).
///
/// # Panics
///
/// Panics if `mid > len`. For a non-panicking alternative see
/// [`split_at_checked`](slice::split_at_checked).
///
/// # Examples
///
/// ```
/// let v = ['a', 'b', 'c'];
///
/// {
/// let (left, right) = v.split_at(0);
/// assert_eq!(left, []);
/// assert_eq!(right, ['a', 'b', 'c']);
/// }
///
/// {
/// let (left, right) = v.split_at(2);
/// assert_eq!(left, ['a', 'b']);
/// assert_eq!(right, ['c']);
/// }
///
/// {
/// let (left, right) = v.split_at(3);
/// assert_eq!(left, ['a', 'b', 'c']);
/// assert_eq!(right, []);
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_split_at_not_mut", since = "1.71.0")]
#[inline]
#[track_caller]
#[must_use]
pub const fn split_at(&self, mid: usize) -> (&[T], &[T]) {
match self.split_at_checked(mid) {
Some(pair) => pair,
None => panic!("mid > len"),
}
}
/// Divides one mutable slice into two at an index.
///
/// The first will contain all indices from `[0, mid)` (excluding
/// the index `mid` itself) and the second will contain all
/// indices from `[mid, len)` (excluding the index `len` itself).
///
/// # Panics
///
/// Panics if `mid > len`. For a non-panicking alternative see
/// [`split_at_mut_checked`](slice::split_at_mut_checked).
///
/// # Examples
///
/// ```
/// let mut v = [1, 0, 3, 0, 5, 6];
/// let (left, right) = v.split_at_mut(2);
/// assert_eq!(left, [1, 0]);
/// assert_eq!(right, [3, 0, 5, 6]);
/// left[1] = 2;
/// right[1] = 4;
/// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
#[track_caller]
#[must_use]
#[rustc_const_stable(feature = "const_slice_split_at_mut", since = "1.83.0")]
pub const fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
match self.split_at_mut_checked(mid) {
Some(pair) => pair,
None => panic!("mid > len"),
}
}
/// Divides one slice into two at an index, without doing bounds checking.
///
/// The first will contain all indices from `[0, mid)` (excluding
/// the index `mid` itself) and the second will contain all
/// indices from `[mid, len)` (excluding the index `len` itself).
///
/// For a safe alternative see [`split_at`].
///
/// # Safety
///
/// Calling this method with an out-of-bounds index is *[undefined behavior]*
/// even if the resulting reference is not used. The caller has to ensure that
/// `0 <= mid <= self.len()`.
///
/// [`split_at`]: slice::split_at
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
///
/// # Examples
///
/// ```
/// let v = ['a', 'b', 'c'];
///
/// unsafe {
/// let (left, right) = v.split_at_unchecked(0);
/// assert_eq!(left, []);
/// assert_eq!(right, ['a', 'b', 'c']);
/// }
///
/// unsafe {
/// let (left, right) = v.split_at_unchecked(2);
/// assert_eq!(left, ['a', 'b']);
/// assert_eq!(right, ['c']);
/// }
///
/// unsafe {
/// let (left, right) = v.split_at_unchecked(3);
/// assert_eq!(left, ['a', 'b', 'c']);
/// assert_eq!(right, []);
/// }
/// ```
#[stable(feature = "slice_split_at_unchecked", since = "1.79.0")]
#[rustc_const_stable(feature = "const_slice_split_at_unchecked", since = "1.77.0")]
#[inline]
#[must_use]
#[track_caller]
pub const unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
// FIXME(const-hack): the const function `from_raw_parts` is used to make this
// function const; previously the implementation used
// `(self.get_unchecked(..mid), self.get_unchecked(mid..))`
let len = self.len();
let ptr = self.as_ptr();
assert_unsafe_precondition!(
check_library_ub,
"slice::split_at_unchecked requires the index to be within the slice",
(mid: usize = mid, len: usize = len) => mid <= len,
);
// SAFETY: Caller has to check that `0 <= mid <= self.len()`
unsafe { (from_raw_parts(ptr, mid), from_raw_parts(ptr.add(mid), unchecked_sub(len, mid))) }
}
/// Divides one mutable slice into two at an index, without doing bounds checking.
///
/// The first will contain all indices from `[0, mid)` (excluding
/// the index `mid` itself) and the second will contain all
/// indices from `[mid, len)` (excluding the index `len` itself).
///
/// For a safe alternative see [`split_at_mut`].
///
/// # Safety
///
/// Calling this method with an out-of-bounds index is *[undefined behavior]*
/// even if the resulting reference is not used. The caller has to ensure that
/// `0 <= mid <= self.len()`.
///
/// [`split_at_mut`]: slice::split_at_mut
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
///
/// # Examples
///
/// ```
/// let mut v = [1, 0, 3, 0, 5, 6];
/// // scoped to restrict the lifetime of the borrows
/// unsafe {
/// let (left, right) = v.split_at_mut_unchecked(2);
/// assert_eq!(left, [1, 0]);
/// assert_eq!(right, [3, 0, 5, 6]);
/// left[1] = 2;
/// right[1] = 4;
/// }
/// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
/// ```
#[stable(feature = "slice_split_at_unchecked", since = "1.79.0")]
#[rustc_const_stable(feature = "const_slice_split_at_mut", since = "1.83.0")]
#[inline]
#[must_use]
#[track_caller]
pub const unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
let len = self.len();
let ptr = self.as_mut_ptr();
assert_unsafe_precondition!(
check_library_ub,
"slice::split_at_mut_unchecked requires the index to be within the slice",
(mid: usize = mid, len: usize = len) => mid <= len,
);
// SAFETY: Caller has to check that `0 <= mid <= self.len()`.
//
// `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
// is fine.
unsafe {
(
from_raw_parts_mut(ptr, mid),
from_raw_parts_mut(ptr.add(mid), unchecked_sub(len, mid)),
)
}
}
/// Divides one slice into two at an index, returning `None` if the slice is
/// too short.
///
/// If `mid ≤ len` returns a pair of slices where the first will contain all
/// indices from `[0, mid)` (excluding the index `mid` itself) and the
/// second will contain all indices from `[mid, len)` (excluding the index
/// `len` itself).
///
/// Otherwise, if `mid > len`, returns `None`.
///
/// # Examples
///
/// ```
/// let v = [1, -2, 3, -4, 5, -6];
///
/// {
/// let (left, right) = v.split_at_checked(0).unwrap();
/// assert_eq!(left, []);
/// assert_eq!(right, [1, -2, 3, -4, 5, -6]);
/// }
///
/// {
/// let (left, right) = v.split_at_checked(2).unwrap();
/// assert_eq!(left, [1, -2]);
/// assert_eq!(right, [3, -4, 5, -6]);
/// }
///
/// {
/// let (left, right) = v.split_at_checked(6).unwrap();
/// assert_eq!(left, [1, -2, 3, -4, 5, -6]);
/// assert_eq!(right, []);
/// }
///
/// assert_eq!(None, v.split_at_checked(7));
/// ```
#[stable(feature = "split_at_checked", since = "1.80.0")]
#[rustc_const_stable(feature = "split_at_checked", since = "1.80.0")]
#[inline]
#[must_use]
pub const fn split_at_checked(&self, mid: usize) -> Option<(&[T], &[T])> {
if mid <= self.len() {
// SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
// fulfills the requirements of `split_at_unchecked`.
Some(unsafe { self.split_at_unchecked(mid) })
} else {
None
}
}
/// Divides one mutable slice into two at an index, returning `None` if the
/// slice is too short.
///
/// If `mid ≤ len` returns a pair of slices where the first will contain all
/// indices from `[0, mid)` (excluding the index `mid` itself) and the
/// second will contain all indices from `[mid, len)` (excluding the index
/// `len` itself).
///
/// Otherwise, if `mid > len`, returns `None`.
///
/// # Examples
///
/// ```
/// let mut v = [1, 0, 3, 0, 5, 6];
///
/// if let Some((left, right)) = v.split_at_mut_checked(2) {
/// assert_eq!(left, [1, 0]);
/// assert_eq!(right, [3, 0, 5, 6]);
/// left[1] = 2;
/// right[1] = 4;
/// }
/// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
///
/// assert_eq!(None, v.split_at_mut_checked(7));
/// ```
#[stable(feature = "split_at_checked", since = "1.80.0")]
#[rustc_const_stable(feature = "const_slice_split_at_mut", since = "1.83.0")]
#[inline]
#[must_use]
pub const fn split_at_mut_checked(&mut self, mid: usize) -> Option<(&mut [T], &mut [T])> {
if mid <= self.len() {
// SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
// fulfills the requirements of `split_at_unchecked`.
Some(unsafe { self.split_at_mut_unchecked(mid) })
} else {
None
}
}
/// Returns an iterator over subslices separated by elements that match
/// `pred`. The matched element is not contained in the subslices.
///
/// # Examples
///
/// ```
/// let slice = [10, 40, 33, 20];
/// let mut iter = slice.split(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[10, 40]);
/// assert_eq!(iter.next().unwrap(), &[20]);
/// assert!(iter.next().is_none());
/// ```
///
/// If the first element is matched, an empty slice will be the first item
/// returned by the iterator. Similarly, if the last element in the slice
/// is matched, an empty slice will be the last item returned by the
/// iterator:
///
/// ```
/// let slice = [10, 40, 33];
/// let mut iter = slice.split(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[10, 40]);
/// assert_eq!(iter.next().unwrap(), &[]);
/// assert!(iter.next().is_none());
/// ```
///
/// If two matched elements are directly adjacent, an empty slice will be
/// present between them:
///
/// ```
/// let slice = [10, 6, 33, 20];
/// let mut iter = slice.split(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[10]);
/// assert_eq!(iter.next().unwrap(), &[]);
/// assert_eq!(iter.next().unwrap(), &[20]);
/// assert!(iter.next().is_none());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
where
F: FnMut(&T) -> bool,
{
Split::new(self, pred)
}
/// Returns an iterator over mutable subslices separated by elements that
/// match `pred`. The matched element is not contained in the subslices.
///
/// # Examples
///
/// ```
/// let mut v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.split_mut(|num| *num % 3 == 0) {
/// group[0] = 1;
/// }
/// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
where
F: FnMut(&T) -> bool,
{
SplitMut::new(self, pred)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred`. The matched element is contained in the end of the previous
/// subslice as a terminator.
///
/// # Examples
///
/// ```
/// let slice = [10, 40, 33, 20];
/// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
/// assert_eq!(iter.next().unwrap(), &[20]);
/// assert!(iter.next().is_none());
/// ```
///
/// If the last element of the slice is matched,
/// that element will be considered the terminator of the preceding slice.
/// That slice will be the last item returned by the iterator.
///
/// ```
/// let slice = [3, 10, 40, 33];
/// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[3]);
/// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
/// assert!(iter.next().is_none());
/// ```
#[stable(feature = "split_inclusive", since = "1.51.0")]
#[inline]
pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
where
F: FnMut(&T) -> bool,
{
SplitInclusive::new(self, pred)
}
/// Returns an iterator over mutable subslices separated by elements that
/// match `pred`. The matched element is contained in the previous
/// subslice as a terminator.
///
/// # Examples
///
/// ```
/// let mut v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
/// let terminator_idx = group.len()-1;
/// group[terminator_idx] = 1;
/// }
/// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
/// ```
#[stable(feature = "split_inclusive", since = "1.51.0")]
#[inline]
pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
where
F: FnMut(&T) -> bool,
{
SplitInclusiveMut::new(self, pred)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred`, starting at the end of the slice and working backwards.
/// The matched element is not contained in the subslices.
///
/// # Examples
///
/// ```
/// let slice = [11, 22, 33, 0, 44, 55];
/// let mut iter = slice.rsplit(|num| *num == 0);
///
/// assert_eq!(iter.next().unwrap(), &[44, 55]);
/// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
/// assert_eq!(iter.next(), None);
/// ```
///
/// As with `split()`, if the first or last element is matched, an empty
/// slice will be the first (or last) item returned by the iterator.
///
/// ```
/// let v = &[0, 1, 1, 2, 3, 5, 8];
/// let mut it = v.rsplit(|n| *n % 2 == 0);
/// assert_eq!(it.next().unwrap(), &[]);
/// assert_eq!(it.next().unwrap(), &[3, 5]);
/// assert_eq!(it.next().unwrap(), &[1, 1]);
/// assert_eq!(it.next().unwrap(), &[]);
/// assert_eq!(it.next(), None);
/// ```
#[stable(feature = "slice_rsplit", since = "1.27.0")]
#[inline]
pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
where
F: FnMut(&T) -> bool,
{
RSplit::new(self, pred)
}
/// Returns an iterator over mutable subslices separated by elements that
/// match `pred`, starting at the end of the slice and working
/// backwards. The matched element is not contained in the subslices.
///
/// # Examples
///
/// ```
/// let mut v = [100, 400, 300, 200, 600, 500];
///
/// let mut count = 0;
/// for group in v.rsplit_mut(|num| *num % 3 == 0) {
/// count += 1;
/// group[0] = count;
/// }
/// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
/// ```
///
#[stable(feature = "slice_rsplit", since = "1.27.0")]
#[inline]
pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
where
F: FnMut(&T) -> bool,
{
RSplitMut::new(self, pred)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred`, limited to returning at most `n` items. The matched element is
/// not contained in the subslices.
///
/// The last element returned, if any, will contain the remainder of the
/// slice.
///
/// # Examples
///
/// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
/// `[20, 60, 50]`):
///
/// ```
/// let v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.splitn(2, |num| *num % 3 == 0) {
/// println!("{group:?}");
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
where
F: FnMut(&T) -> bool,
{
SplitN::new(self.split(pred), n)
}
/// Returns an iterator over mutable subslices separated by elements that match
/// `pred`, limited to returning at most `n` items. The matched element is
/// not contained in the subslices.
///
/// The last element returned, if any, will contain the remainder of the
/// slice.
///
/// # Examples
///
/// ```
/// let mut v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
/// group[0] = 1;
/// }
/// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
where
F: FnMut(&T) -> bool,
{
SplitNMut::new(self.split_mut(pred), n)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred` limited to returning at most `n` items. This starts at the end of
/// the slice and works backwards. The matched element is not contained in
/// the subslices.
///
/// The last element returned, if any, will contain the remainder of the
/// slice.
///
/// # Examples
///
/// Print the slice split once, starting from the end, by numbers divisible
/// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
///
/// ```
/// let v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.rsplitn(2, |num| *num % 3 == 0) {
/// println!("{group:?}");
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
where
F: FnMut(&T) -> bool,
{
RSplitN::new(self.rsplit(pred), n)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred` limited to returning at most `n` items. This starts at the end of
/// the slice and works backwards. The matched element is not contained in
/// the subslices.
///
/// The last element returned, if any, will contain the remainder of the
/// slice.
///
/// # Examples
///
/// ```
/// let mut s = [10, 40, 30, 20, 60, 50];
///
/// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
/// group[0] = 1;
/// }
/// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
where
F: FnMut(&T) -> bool,
{
RSplitNMut::new(self.rsplit_mut(pred), n)
}
/// Splits the slice on the first element that matches the specified
/// predicate.
///
/// If any matching elements are present in the slice, returns the prefix
/// before the match and suffix after. The matching element itself is not
/// included. If no elements match, returns `None`.
///
/// # Examples
///
/// ```
/// #![feature(slice_split_once)]
/// let s = [1, 2, 3, 2, 4];
/// assert_eq!(s.split_once(|&x| x == 2), Some((
/// &[1][..],
/// &[3, 2, 4][..]
/// )));
/// assert_eq!(s.split_once(|&x| x == 0), None);
/// ```
#[unstable(feature = "slice_split_once", issue = "112811")]
#[inline]
pub fn split_once<F>(&self, pred: F) -> Option<(&[T], &[T])>
where
F: FnMut(&T) -> bool,
{
let index = self.iter().position(pred)?;
// Slice bounds checks optimized are away (as of June 2026)
Some((&self[..index], &self[index + 1..]))
}
/// Splits the slice on the last element that matches the specified
/// predicate.
///
/// If any matching elements are present in the slice, returns the prefix
/// before the match and suffix after. The matching element itself is not
/// included. If no elements match, returns `None`.
///
/// # Examples
///
/// ```
/// #![feature(slice_split_once)]
/// let s = [1, 2, 3, 2, 4];
/// assert_eq!(s.rsplit_once(|&x| x == 2), Some((
/// &[1, 2, 3][..],
/// &[4][..]
/// )));
/// assert_eq!(s.rsplit_once(|&x| x == 0), None);
/// ```
#[unstable(feature = "slice_split_once", issue = "112811")]
#[inline]
pub fn rsplit_once<F>(&self, pred: F) -> Option<(&[T], &[T])>
where
F: FnMut(&T) -> bool,
{
let index = self.iter().rposition(pred)?;
// Slice bounds checks optimized are away (as of June 2026)
Some((&self[..index], &self[index + 1..]))
}
/// Returns `true` if the slice contains an element with the given value.
///
/// This operation is *O*(*n*).
///
/// Note that if you have a sorted slice, [`binary_search`] may be faster.
///
/// [`binary_search`]: slice::binary_search
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert!(v.contains(&30));
/// assert!(!v.contains(&50));
/// ```
///
/// If you do not have a `&T`, but some other value that you can compare
/// with one (for example, `String` implements `PartialEq<str>`), you can
/// use `iter().any`:
///
/// ```
/// let v = [String::from("hello"), String::from("world")]; // slice of `String`
/// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
/// assert!(!v.iter().any(|e| e == "hi"));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
#[must_use]
pub fn contains(&self, x: &T) -> bool
where
T: PartialEq,
{
cmp::SliceContains::slice_contains(x, self)
}
/// Returns `true` if `needle` is a prefix of the slice or equal to the slice.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert!(v.starts_with(&[10]));
/// assert!(v.starts_with(&[10, 40]));
/// assert!(v.starts_with(&v));
/// assert!(!v.starts_with(&[50]));
/// assert!(!v.starts_with(&[10, 50]));
/// ```
///
/// Always returns `true` if `needle` is an empty slice:
///
/// ```
/// let v = &[10, 40, 30];
/// assert!(v.starts_with(&[]));
/// let v: &[u8] = &[];
/// assert!(v.starts_with(&[]));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[must_use]
pub fn starts_with(&self, needle: &[T]) -> bool
where
T: PartialEq,
{
let n = needle.len();
self.len() >= n && needle == &self[..n]
}
/// Returns `true` if `needle` is a suffix of the slice or equal to the slice.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert!(v.ends_with(&[30]));
/// assert!(v.ends_with(&[40, 30]));
/// assert!(v.ends_with(&v));
/// assert!(!v.ends_with(&[50]));
/// assert!(!v.ends_with(&[50, 30]));
/// ```
///
/// Always returns `true` if `needle` is an empty slice:
///
/// ```
/// let v = &[10, 40, 30];
/// assert!(v.ends_with(&[]));
/// let v: &[u8] = &[];
/// assert!(v.ends_with(&[]));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[must_use]
pub fn ends_with(&self, needle: &[T]) -> bool
where
T: PartialEq,
{
let (m, n) = (self.len(), needle.len());
m >= n && needle == &self[m - n..]
}
/// Returns a subslice with the prefix removed.
///
/// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
/// If `prefix` is empty, simply returns the original slice. If `prefix` is equal to the
/// original slice, returns an empty slice.
///
/// If the slice does not start with `prefix`, returns `None`.
///
/// # Examples
///
/// ```
/// let v = &[10, 40, 30];
/// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
/// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
/// assert_eq!(v.strip_prefix(&[10, 40, 30]), Some(&[][..]));
/// assert_eq!(v.strip_prefix(&[50]), None);
/// assert_eq!(v.strip_prefix(&[10, 50]), None);
///
/// let prefix : &str = "he";
/// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
/// Some(b"llo".as_ref()));
/// ```
#[must_use = "returns the subslice without modifying the original"]
#[stable(feature = "slice_strip", since = "1.51.0")]
pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
where
T: PartialEq,
{
// This function will need rewriting if and when SlicePattern becomes more sophisticated.
let prefix = prefix.as_slice();
let n = prefix.len();
if n <= self.len() {
let (head, tail) = self.split_at(n);
if head == prefix {
return Some(tail);
}
}
None
}
/// Returns a subslice with the suffix removed.
///
/// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
/// If `suffix` is empty, simply returns the original slice. If `suffix` is equal to the
/// original slice, returns an empty slice.
///
/// If the slice does not end with `suffix`, returns `None`.
///
/// # Examples
///
/// ```
/// let v = &[10, 40, 30];
/// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
/// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
/// assert_eq!(v.strip_suffix(&[10, 40, 30]), Some(&[][..]));
/// assert_eq!(v.strip_suffix(&[50]), None);
/// assert_eq!(v.strip_suffix(&[50, 30]), None);
/// ```
#[must_use = "returns the subslice without modifying the original"]
#[stable(feature = "slice_strip", since = "1.51.0")]
pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
where
T: PartialEq,
{
// This function will need rewriting if and when SlicePattern becomes more sophisticated.
let suffix = suffix.as_slice();
let (len, n) = (self.len(), suffix.len());
if n <= len {
let (head, tail) = self.split_at(len - n);
if tail == suffix {
return Some(head);
}
}
None
}
/// Returns a subslice with the prefix and suffix removed.
///
/// If the slice starts with `prefix`, ends with `suffix`, and
/// the prefix and suffix don't overlap, returns the subslice after
/// the prefix and before the suffix, wrapped in `Some`.
///
/// If the slice does not start with `prefix`, does not end with `suffix`,
/// or the prefix and suffix overlap in the slice, returns `None`.
///
/// # Examples
///
/// ```
/// let v = &[10, 50, 40, 30];
/// assert_eq!(v.strip_circumfix(&[10], &[30]), Some(&[50, 40][..]));
/// assert_eq!(v.strip_circumfix(&[10], &[40, 30]), Some(&[50][..]));
/// assert_eq!(v.strip_circumfix(&[10, 50], &[40, 30]), Some(&[][..]));
/// assert_eq!(v.strip_circumfix(&[50], &[30]), None);
/// assert_eq!(v.strip_circumfix(&[10], &[40]), None);
/// assert_eq!(v.strip_circumfix(&[], &[40, 30]), Some(&[10, 50][..]));
/// assert_eq!(v.strip_circumfix(&[10, 50], &[]), Some(&[40, 30][..]));
/// assert_eq!(v.strip_circumfix(&[10, 50, 40], &[50, 40, 30]), None);
/// ```
#[must_use = "returns the subslice without modifying the original"]
#[stable(feature = "strip_circumfix", since = "1.98.0")]
pub fn strip_circumfix<S, P>(&self, prefix: &P, suffix: &S) -> Option<&[T]>
where
T: PartialEq,
S: SlicePattern<Item = T> + ?Sized,
P: SlicePattern<Item = T> + ?Sized,
{
self.strip_prefix(prefix)?.strip_suffix(suffix)
}
/// Returns a subslice with the optional prefix removed.
///
/// If the slice starts with `prefix`, returns the subslice after the prefix. If `prefix`
/// is empty or the slice does not start with `prefix`, simply returns the original slice.
/// If `prefix` is equal to the original slice, returns an empty slice.
///
/// # Examples
///
/// ```
/// #![feature(trim_prefix_suffix)]
///
/// let v = &[10, 40, 30];
///
/// // Prefix present - removes it
/// assert_eq!(v.trim_prefix(&[10]), &[40, 30][..]);
/// assert_eq!(v.trim_prefix(&[10, 40]), &[30][..]);
/// assert_eq!(v.trim_prefix(&[10, 40, 30]), &[][..]);
///
/// // Prefix absent - returns original slice
/// assert_eq!(v.trim_prefix(&[50]), &[10, 40, 30][..]);
/// assert_eq!(v.trim_prefix(&[10, 50]), &[10, 40, 30][..]);
///
/// let prefix : &str = "he";
/// assert_eq!(b"hello".trim_prefix(prefix.as_bytes()), b"llo".as_ref());
/// ```
#[must_use = "returns the subslice without modifying the original"]
#[unstable(feature = "trim_prefix_suffix", issue = "142312")]
pub fn trim_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> &[T]
where
T: PartialEq,
{
// This function will need rewriting if and when SlicePattern becomes more sophisticated.
let prefix = prefix.as_slice();
let n = prefix.len();
if n <= self.len() {
let (head, tail) = self.split_at(n);
if head == prefix {
return tail;
}
}
self
}
/// Returns a subslice with the optional suffix removed.
///
/// If the slice ends with `suffix`, returns the subslice before the suffix. If `suffix`
/// is empty or the slice does not end with `suffix`, simply returns the original slice.
/// If `suffix` is equal to the original slice, returns an empty slice.
///
/// # Examples
///
/// ```
/// #![feature(trim_prefix_suffix)]
///
/// let v = &[10, 40, 30];
///
/// // Suffix present - removes it
/// assert_eq!(v.trim_suffix(&[30]), &[10, 40][..]);
/// assert_eq!(v.trim_suffix(&[40, 30]), &[10][..]);
/// assert_eq!(v.trim_suffix(&[10, 40, 30]), &[][..]);
///
/// // Suffix absent - returns original slice
/// assert_eq!(v.trim_suffix(&[50]), &[10, 40, 30][..]);
/// assert_eq!(v.trim_suffix(&[50, 30]), &[10, 40, 30][..]);
/// ```
#[must_use = "returns the subslice without modifying the original"]
#[unstable(feature = "trim_prefix_suffix", issue = "142312")]
pub fn trim_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> &[T]
where
T: PartialEq,
{
// This function will need rewriting if and when SlicePattern becomes more sophisticated.
let suffix = suffix.as_slice();
let (len, n) = (self.len(), suffix.len());
if n <= len {
let (head, tail) = self.split_at(len - n);
if tail == suffix {
return head;
}
}
self
}
/// Binary searches this slice for a given element.
/// If the slice is not sorted, the returned result is unspecified and
/// meaningless.
///
/// If the value is found then [`Result::Ok`] is returned, containing the
/// index of the matching element. If there are multiple matches, then any
/// one of the matches could be returned. The index is chosen
/// deterministically, but is subject to change in future versions of Rust.
/// If the value is not found then [`Result::Err`] is returned, containing
/// the index where a matching element could be inserted while maintaining
/// sorted order.
///
/// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
///
/// [`binary_search_by`]: slice::binary_search_by
/// [`binary_search_by_key`]: slice::binary_search_by_key
/// [`partition_point`]: slice::partition_point
///
/// # Examples
///
/// Looks up a series of four elements. The first is found, with a
/// uniquely determined position; the second and third are not
/// found; the fourth could match any position in `[1, 4]`.
///
/// ```
/// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
///
/// assert_eq!(s.binary_search(&13), Ok(9));
/// assert_eq!(s.binary_search(&4), Err(7));
/// assert_eq!(s.binary_search(&100), Err(13));
/// let r = s.binary_search(&1);
/// assert!(match r { Ok(1..=4) => true, _ => false, });
/// ```
///
/// If you want to find that whole *range* of matching items, rather than
/// an arbitrary matching one, that can be done using [`partition_point`]:
/// ```
/// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
///
/// let low = s.partition_point(|x| x < &1);
/// assert_eq!(low, 1);
/// let high = s.partition_point(|x| x <= &1);
/// assert_eq!(high, 5);
/// let r = s.binary_search(&1);
/// assert!((low..high).contains(&r.unwrap()));
///
/// assert!(s[..low].iter().all(|&x| x < 1));
/// assert!(s[low..high].iter().all(|&x| x == 1));
/// assert!(s[high..].iter().all(|&x| x > 1));
///
/// // For something not found, the "range" of equal items is empty
/// assert_eq!(s.partition_point(|x| x < &11), 9);
/// assert_eq!(s.partition_point(|x| x <= &11), 9);
/// assert_eq!(s.binary_search(&11), Err(9));
/// ```
///
/// If you want to insert an item to a sorted vector, while maintaining
/// sort order, consider using [`partition_point`]:
///
/// ```
/// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
/// let num = 42;
/// let idx = s.partition_point(|&x| x <= num);
/// // If `num` is unique, `s.partition_point(|&x| x < num)` (with `<`) is equivalent to
/// // `s.binary_search(&num).unwrap_or_else(|x| x)`, but using `<=` will allow `insert`
/// // to shift less elements.
/// s.insert(idx, num);
/// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
/// ```
#[rustc_const_unstable(feature = "const_binary_search", issue = "159532")]
#[stable(feature = "rust1", since = "1.0.0")]
pub const fn binary_search(&self, x: &T) -> Result<usize, usize>
where
T: [const] Ord,
{
self.binary_search_by(const |p| p.cmp(x))
}
/// Binary searches this slice with a comparator function.
///
/// The comparator function should return an order code that indicates
/// whether its argument is `Less`, `Equal` or `Greater` the desired
/// target.
/// If the slice is not sorted or if the comparator function does not
/// implement an order consistent with the sort order of the underlying
/// slice, the returned result is unspecified and meaningless.
///
/// If the value is found then [`Result::Ok`] is returned, containing the
/// index of the matching element. If there are multiple matches, then any
/// one of the matches could be returned. The index is chosen
/// deterministically, but is subject to change in future versions of Rust.
/// If the value is not found then [`Result::Err`] is returned, containing
/// the index where a matching element could be inserted while maintaining
/// sorted order.
///
/// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
///
/// [`binary_search`]: slice::binary_search
/// [`binary_search_by_key`]: slice::binary_search_by_key
/// [`partition_point`]: slice::partition_point
///
/// # Examples
///
/// Looks up a series of four elements. The first is found, with a
/// uniquely determined position; the second and third are not
/// found; the fourth could match any position in `[1, 4]`.
///
/// ```
/// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
///
/// let seek = 13;
/// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
/// let seek = 4;
/// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
/// let seek = 100;
/// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
/// let seek = 1;
/// let r = s.binary_search_by(|probe| probe.cmp(&seek));
/// assert!(match r { Ok(1..=4) => true, _ => false, });
/// ```
#[rustc_const_unstable(feature = "const_binary_search", issue = "159532")]
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub const fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
where
F: [const] FnMut(&'a T) -> Ordering + [const] Destruct,
{
let mut size = self.len();
if size == 0 {
return Err(0);
}
let mut base = 0usize;
// This loop intentionally doesn't have an early exit if the comparison
// returns Equal. We want the number of loop iterations to depend *only*
// on the size of the input slice so that the CPU can reliably predict
// the loop count.
while size > 1 {
let half = size / 2;
let mid = base + half;
// SAFETY: the call is made safe by the following invariants:
// - `mid >= 0`: by definition
// - `mid < size`: `mid = size / 2 + size / 4 + size / 8 ...`
let cmp = f(unsafe { self.get_unchecked(mid) });
// Binary search interacts poorly with branch prediction, so force
// the compiler to use conditional moves if supported by the target
// architecture.
base = hint::select_unpredictable(cmp == Greater, base, mid);
// This is imprecise in the case where `size` is odd and the
// comparison returns Greater: the mid element still gets included
// by `size` even though it's known to be larger than the element
// being searched for.
//
// This is fine though: we gain more performance by keeping the
// loop iteration count invariant (and thus predictable) than we
// lose from considering one additional element.
size -= half;
}
// SAFETY: base is always in [0, size) because base <= mid.
let cmp = f(unsafe { self.get_unchecked(base) });
if cmp == Equal {
// SAFETY: same as the `get_unchecked` above.
unsafe { hint::assert_unchecked(base < self.len()) };
Ok(base)
} else {
let result = base + (cmp == Less) as usize;
// SAFETY: same as the `get_unchecked` above.
// Note that this is `<=`, unlike the assume in the `Ok` path.
unsafe { hint::assert_unchecked(result <= self.len()) };
Err(result)
}
}
/// Binary searches this slice with a key extraction function.
///
/// Assumes that the slice is sorted by the key, for instance with
/// [`sort_by_key`] using the same key extraction function.
/// If the slice is not sorted by the key, the returned result is
/// unspecified and meaningless.
///
/// If the value is found then [`Result::Ok`] is returned, containing the
/// index of the matching element. If there are multiple matches, then any
/// one of the matches could be returned. The index is chosen
/// deterministically, but is subject to change in future versions of Rust.
/// If the value is not found then [`Result::Err`] is returned, containing
/// the index where a matching element could be inserted while maintaining
/// sorted order.
///
/// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
///
/// [`sort_by_key`]: slice::sort_by_key
/// [`binary_search`]: slice::binary_search
/// [`binary_search_by`]: slice::binary_search_by
/// [`partition_point`]: slice::partition_point
///
/// # Examples
///
/// Looks up a series of four elements in a slice of pairs sorted by
/// their second elements. The first is found, with a uniquely
/// determined position; the second and third are not found; the
/// fourth could match any position in `[1, 4]`.
///
/// ```
/// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
/// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
/// (1, 21), (2, 34), (4, 55)];
///
/// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
/// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
/// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
/// let r = s.binary_search_by_key(&1, |&(a, b)| b);
/// assert!(match r { Ok(1..=4) => true, _ => false, });
/// ```
// Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
// in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
// This breaks links when slice is displayed in core, but changing it to use relative links
// would break when the item is re-exported. So allow the core links to be broken for now.
#[allow(rustdoc::broken_intra_doc_links)]
#[rustc_const_unstable(feature = "const_binary_search", issue = "159532")]
#[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
#[inline]
pub const fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
where
F: [const] FnMut(&'a T) -> B + [const] Destruct,
B: [const] Ord + [const] Destruct,
{
self.binary_search_by(const |k| f(k).cmp(b))
}
/// Sorts the slice in ascending order **without** preserving the initial order of equal elements.
///
/// This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not
/// allocate), and *O*(*n* \* log(*n*)) worst-case.
///
/// If the implementation of [`Ord`] for `T` does not implement a [total order], the function
/// may panic; even if the function exits normally, the resulting order of elements in the slice
/// is unspecified. See also the note on panicking below.
///
/// For example `|a, b| (a - b).cmp(a)` is a comparison function that is neither transitive nor
/// reflexive nor total, `a < b < c < a` with `a = 1, b = 2, c = 3`. For more information and
/// examples see the [`Ord`] documentation.
///
///
/// All original elements will remain in the slice and any possible modifications via interior
/// mutability are observed in the input. Same is true if the implementation of [`Ord`] for `T` panics.
///
/// Sorting types that only implement [`PartialOrd`] such as [`f32`] and [`f64`] require
/// additional precautions. For example, `f32::NAN != f32::NAN`, which doesn't fulfill the
/// reflexivity requirement of [`Ord`]. By using an alternative comparison function with
/// `slice::sort_unstable_by` such as [`f32::total_cmp`] or [`f64::total_cmp`] that defines a
/// [total order] users can sort slices containing floating-point values. Alternatively, if all
/// values in the slice are guaranteed to be in a subset for which [`PartialOrd::partial_cmp`]
/// forms a [total order], it's possible to sort the slice with `sort_unstable_by(|a, b|
/// a.partial_cmp(b).unwrap())`.
///
/// # Current implementation
///
/// The current implementation is based on [ipnsort] by Lukas Bergdoll and Orson Peters, which
/// combines the fast average case of quicksort with the fast worst case of heapsort, achieving
/// linear time on fully sorted and reversed inputs. On inputs with k distinct elements, the
/// expected time to sort the data is *O*(*n* \* log(*k*)).
///
/// It is typically faster than stable sorting, except in a few special cases, e.g., when the
/// slice is partially sorted.
///
/// # Panics
///
/// May panic if the implementation of [`Ord`] for `T` does not implement a [total order], or if
/// the [`Ord`] implementation panics.
///
/// # Examples
///
/// ```
/// let mut v = [4, -5, 1, -3, 2];
///
/// v.sort_unstable();
/// assert_eq!(v, [-5, -3, 1, 2, 4]);
/// ```
///
/// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort
/// [total order]: https://en.wikipedia.org/wiki/Total_order
#[stable(feature = "sort_unstable", since = "1.20.0")]
#[inline]
pub fn sort_unstable(&mut self)
where
T: Ord,
{
sort::unstable::sort(self, &mut T::lt);
}
/// Sorts the slice in ascending order with a comparison function, **without** preserving the
/// initial order of equal elements.
///
/// This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not
/// allocate), and *O*(*n* \* log(*n*)) worst-case.
///
/// If the comparison function `compare` does not implement a [total order], the function
/// may panic; even if the function exits normally, the resulting order of elements in the slice
/// is unspecified. See also the note on panicking below.
///
/// For example `|a, b| (a - b).cmp(a)` is a comparison function that is neither transitive nor
/// reflexive nor total, `a < b < c < a` with `a = 1, b = 2, c = 3`. For more information and
/// examples see the [`Ord`] documentation.
///
/// All original elements will remain in the slice and any possible modifications via interior
/// mutability are observed in the input. Same is true if `compare` panics.
///
/// # Current implementation
///
/// The current implementation is based on [ipnsort] by Lukas Bergdoll and Orson Peters, which
/// combines the fast average case of quicksort with the fast worst case of heapsort, achieving
/// linear time on fully sorted and reversed inputs. On inputs with k distinct elements, the
/// expected time to sort the data is *O*(*n* \* log(*k*)).
///
/// It is typically faster than stable sorting, except in a few special cases, e.g., when the
/// slice is partially sorted.
///
/// # Panics
///
/// May panic if the `compare` does not implement a [total order], or if
/// the `compare` itself panics.
///
/// # Examples
///
/// ```
/// let mut v = [4, -5, 1, -3, 2];
/// v.sort_unstable_by(|a, b| a.cmp(b));
/// assert_eq!(v, [-5, -3, 1, 2, 4]);
///
/// // reverse sorting
/// v.sort_unstable_by(|a, b| b.cmp(a));
/// assert_eq!(v, [4, 2, 1, -3, -5]);
/// ```
///
/// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort
/// [total order]: https://en.wikipedia.org/wiki/Total_order
#[stable(feature = "sort_unstable", since = "1.20.0")]
#[inline]
pub fn sort_unstable_by<F>(&mut self, mut compare: F)
where
F: FnMut(&T, &T) -> Ordering,
{
sort::unstable::sort(self, &mut |a, b| compare(a, b) == Ordering::Less);
}
/// Sorts the slice in ascending order with a key extraction function, **without** preserving
/// the initial order of equal elements.
///
/// This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not
/// allocate), and *O*(*n* \* log(*n*)) worst-case.
///
/// If the implementation of [`Ord`] for `K` does not implement a [total order], the function
/// may panic; even if the function exits normally, the resulting order of elements in the slice
/// is unspecified. See also the note on panicking below.
///
/// For example `|a, b| (a - b).cmp(a)` is a comparison function that is neither transitive nor
/// reflexive nor total, `a < b < c < a` with `a = 1, b = 2, c = 3`. For more information and
/// examples see the [`Ord`] documentation.
///
/// All original elements will remain in the slice and any possible modifications via interior
/// mutability are observed in the input. Same is true if the implementation of [`Ord`] for `K` panics.
///
/// # Current implementation
///
/// The current implementation is based on [ipnsort] by Lukas Bergdoll and Orson Peters, which
/// combines the fast average case of quicksort with the fast worst case of heapsort, achieving
/// linear time on fully sorted and reversed inputs. On inputs with k distinct elements, the
/// expected time to sort the data is *O*(*n* \* log(*k*)).
///
/// It is typically faster than stable sorting, except in a few special cases, e.g., when the
/// slice is partially sorted.
///
/// # Panics
///
/// May panic if the implementation of [`Ord`] for `K` does not implement a [total order], or if
/// the [`Ord`] implementation panics.
///
/// # Examples
///
/// ```
/// let mut v = [4i32, -5, 1, -3, 2];
///
/// v.sort_unstable_by_key(|k| k.abs());
/// assert_eq!(v, [1, 2, -3, 4, -5]);
/// ```
///
/// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort
/// [total order]: https://en.wikipedia.org/wiki/Total_order
#[stable(feature = "sort_unstable", since = "1.20.0")]
#[inline]
pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
where
F: FnMut(&T) -> K,
K: Ord,
{
sort::unstable::sort(self, &mut |a, b| f(a).lt(&f(b)));
}
/// Partially sorts the slice in ascending order **without** preserving the initial order of equal elements.
///
/// Upon completion, for the specified range `start..end`, it's guaranteed that:
///
/// 1. Every element in `self[..start]` is smaller than or equal to
/// 2. Every element in `self[start..end]`, which is sorted, and smaller than or equal to
/// 3. Every element in `self[end..]`.
///
/// This partial sort is unstable, meaning it may reorder equal elements in the specified range.
/// It may reorder elements outside the specified range as well, but the guarantees above still hold.
///
/// This partial sort is in-place (i.e., does not allocate), and *O*(*n* + *k* \* log(*k*)) worst-case,
/// where *n* is the length of the slice and *k* is the length of the specified range.
///
/// See the documentation of [`sort_unstable`] for implementation notes.
///
/// # Panics
///
/// May panic if the implementation of [`Ord`] for `T` does not implement a total order, or if
/// the [`Ord`] implementation panics, or if the specified range is out of bounds.
///
/// # Examples
///
/// ```
/// #![feature(slice_partial_sort_unstable)]
///
/// let mut v = [4, -5, 1, -3, 2];
///
/// // empty range at the beginning, nothing changed
/// v.partial_sort_unstable(0..0);
/// assert_eq!(v, [4, -5, 1, -3, 2]);
///
/// // empty range in the middle, partitioning the slice
/// v.partial_sort_unstable(2..2);
/// for i in 0..2 {
/// assert!(v[i] <= v[2]);
/// }
/// for i in 3..v.len() {
/// assert!(v[2] <= v[i]);
/// }
///
/// // single element range, same as select_nth_unstable
/// v.partial_sort_unstable(2..3);
/// for i in 0..2 {
/// assert!(v[i] <= v[2]);
/// }
/// for i in 3..v.len() {
/// assert!(v[2] <= v[i]);
/// }
///
/// // partial sort a subrange
/// v.partial_sort_unstable(1..4);
/// assert_eq!(&v[1..4], [-3, 1, 2]);
///
/// // partial sort the whole range, same as sort_unstable
/// v.partial_sort_unstable(..);
/// assert_eq!(v, [-5, -3, 1, 2, 4]);
/// ```
///
/// [`sort_unstable`]: slice::sort_unstable
#[unstable(feature = "slice_partial_sort_unstable", issue = "149046")]
#[inline]
pub fn partial_sort_unstable<R>(&mut self, range: R)
where
T: Ord,
R: RangeBounds<usize>,
{
sort::unstable::partial_sort(self, range, T::lt);
}
/// Partially sorts the slice in ascending order with a comparison function, **without**
/// preserving the initial order of equal elements.
///
/// Upon completion, for the specified range `start..end`, it's guaranteed that:
///
/// 1. Every element in `self[..start]` is smaller than or equal to
/// 2. Every element in `self[start..end]`, which is sorted, and smaller than or equal to
/// 3. Every element in `self[end..]`.
///
/// This partial sort is unstable, meaning it may reorder equal elements in the specified range.
/// It may reorder elements outside the specified range as well, but the guarantees above still hold.
///
/// This partial sort is in-place (i.e., does not allocate), and *O*(*n* + *k* \* log(*k*)) worst-case,
/// where *n* is the length of the slice and *k* is the length of the specified range.
///
/// See the documentation of [`sort_unstable_by`] for implementation notes.
///
/// # Panics
///
/// May panic if the `compare` does not implement a total order, or if
/// the `compare` itself panics, or if the specified range is out of bounds.
///
/// # Examples
///
/// ```
/// #![feature(slice_partial_sort_unstable)]
///
/// let mut v = [4, -5, 1, -3, 2];
///
/// // empty range at the beginning, nothing changed
/// v.partial_sort_unstable_by(0..0, |a, b| b.cmp(a));
/// assert_eq!(v, [4, -5, 1, -3, 2]);
///
/// // empty range in the middle, partitioning the slice
/// v.partial_sort_unstable_by(2..2, |a, b| b.cmp(a));
/// for i in 0..2 {
/// assert!(v[i] >= v[2]);
/// }
/// for i in 3..v.len() {
/// assert!(v[2] >= v[i]);
/// }
///
/// // single element range, same as select_nth_unstable
/// v.partial_sort_unstable_by(2..3, |a, b| b.cmp(a));
/// for i in 0..2 {
/// assert!(v[i] >= v[2]);
/// }
/// for i in 3..v.len() {
/// assert!(v[2] >= v[i]);
/// }
///
/// // partial sort a subrange
/// v.partial_sort_unstable_by(1..4, |a, b| b.cmp(a));
/// assert_eq!(&v[1..4], [2, 1, -3]);
///
/// // partial sort the whole range, same as sort_unstable
/// v.partial_sort_unstable_by(.., |a, b| b.cmp(a));
/// assert_eq!(v, [4, 2, 1, -3, -5]);
/// ```
///
/// [`sort_unstable_by`]: slice::sort_unstable_by
#[unstable(feature = "slice_partial_sort_unstable", issue = "149046")]
#[inline]
pub fn partial_sort_unstable_by<F, R>(&mut self, range: R, mut compare: F)
where
F: FnMut(&T, &T) -> Ordering,
R: RangeBounds<usize>,
{
sort::unstable::partial_sort(self, range, |a, b| compare(a, b) == Less);
}
/// Partially sorts the slice in ascending order with a key extraction function, **without**
/// preserving the initial order of equal elements.
///
/// Upon completion, for the specified range `start..end`, it's guaranteed that:
///
/// 1. Every element in `self[..start]` is smaller than or equal to
/// 2. Every element in `self[start..end]`, which is sorted, and smaller than or equal to
/// 3. Every element in `self[end..]`.
///
/// This partial sort is unstable, meaning it may reorder equal elements in the specified range.
/// It may reorder elements outside the specified range as well, but the guarantees above still hold.
///
/// This partial sort is in-place (i.e., does not allocate), and *O*(*n* + *k* \* log(*k*)) worst-case,
/// where *n* is the length of the slice and *k* is the length of the specified range.
///
/// See the documentation of [`sort_unstable_by_key`] for implementation notes.
///
/// # Panics
///
/// May panic if the implementation of [`Ord`] for `K` does not implement a total order, or if
/// the [`Ord`] implementation panics, or if the specified range is out of bounds.
///
/// # Examples
///
/// ```
/// #![feature(slice_partial_sort_unstable)]
///
/// let mut v = [4i32, -5, 1, -3, 2];
///
/// // empty range at the beginning, nothing changed
/// v.partial_sort_unstable_by_key(0..0, |k| k.abs());
/// assert_eq!(v, [4, -5, 1, -3, 2]);
///
/// // empty range in the middle, partitioning the slice
/// v.partial_sort_unstable_by_key(2..2, |k| k.abs());
/// for i in 0..2 {
/// assert!(v[i].abs() <= v[2].abs());
/// }
/// for i in 3..v.len() {
/// assert!(v[2].abs() <= v[i].abs());
/// }
///
/// // single element range, same as select_nth_unstable
/// v.partial_sort_unstable_by_key(2..3, |k| k.abs());
/// for i in 0..2 {
/// assert!(v[i].abs() <= v[2].abs());
/// }
/// for i in 3..v.len() {
/// assert!(v[2].abs() <= v[i].abs());
/// }
///
/// // partial sort a subrange
/// v.partial_sort_unstable_by_key(1..4, |k| k.abs());
/// assert_eq!(&v[1..4], [2, -3, 4]);
///
/// // partial sort the whole range, same as sort_unstable
/// v.partial_sort_unstable_by_key(.., |k| k.abs());
/// assert_eq!(v, [1, 2, -3, 4, -5]);
/// ```
///
/// [`sort_unstable_by_key`]: slice::sort_unstable_by_key
#[unstable(feature = "slice_partial_sort_unstable", issue = "149046")]
#[inline]
pub fn partial_sort_unstable_by_key<K, F, R>(&mut self, range: R, mut f: F)
where
F: FnMut(&T) -> K,
K: Ord,
R: RangeBounds<usize>,
{
sort::unstable::partial_sort(self, range, |a, b| f(a).lt(&f(b)));
}
/// Reorders the slice such that the element at `index` is at a sort-order position. All
/// elements before `index` will be `<=` to this value, and all elements after will be `>=` to
/// it.
///
/// This reordering is unstable (i.e. any element that compares equal to the nth element may end
/// up at that position), in-place (i.e. does not allocate), and runs in *O*(*n*) time. This
/// function is also known as "kth element" in other libraries.
///
/// Returns a triple that partitions the reordered slice:
///
/// * The unsorted subslice before `index`, whose elements all satisfy `x <= self[index]`.
///
/// * The element at `index`.
///
/// * The unsorted subslice after `index`, whose elements all satisfy `x >= self[index]`.
///
/// # Current implementation
///
/// The current algorithm is an introselect implementation based on [ipnsort] by Lukas Bergdoll
/// and Orson Peters, which is also the basis for [`sort_unstable`]. The fallback algorithm is
/// Median of Medians using Tukey's Ninther for pivot selection, which guarantees linear runtime
/// for all inputs.
///
/// [`sort_unstable`]: slice::sort_unstable
///
/// # Panics
///
/// Panics when `index >= len()`, and so always panics on empty slices.
///
/// May panic if the implementation of [`Ord`] for `T` does not implement a [total order].
///
/// # Examples
///
/// ```
/// let mut v = [-5i32, 4, 2, -3, 1];
///
/// // Find the items `<=` to the median, the median itself, and the items `>=` to it.
/// let (lesser, median, greater) = v.select_nth_unstable(2);
///
/// assert!(lesser == [-3, -5] || lesser == [-5, -3]);
/// assert_eq!(median, &mut 1);
/// assert!(greater == [4, 2] || greater == [2, 4]);
///
/// // We are only guaranteed the slice will be one of the following, based on the way we sort
/// // about the specified index.
/// assert!(v == [-3, -5, 1, 2, 4] ||
/// v == [-5, -3, 1, 2, 4] ||
/// v == [-3, -5, 1, 4, 2] ||
/// v == [-5, -3, 1, 4, 2]);
/// ```
///
/// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort
/// [total order]: https://en.wikipedia.org/wiki/Total_order
#[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
#[inline]
pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
where
T: Ord,
{
sort::select::partition_at_index(self, index, T::lt)
}
/// Reorders the slice with a comparator function such that the element at `index` is at a
/// sort-order position. All elements before `index` will be `<=` to this value, and all
/// elements after will be `>=` to it, according to the comparator function.
///
/// This reordering is unstable (i.e. any element that compares equal to the nth element may end
/// up at that position), in-place (i.e. does not allocate), and runs in *O*(*n*) time. This
/// function is also known as "kth element" in other libraries.
///
/// Returns a triple partitioning the reordered slice:
///
/// * The unsorted subslice before `index`, whose elements all satisfy
/// `compare(x, self[index]).is_le()`.
///
/// * The element at `index`.
///
/// * The unsorted subslice after `index`, whose elements all satisfy
/// `compare(x, self[index]).is_ge()`.
///
/// # Current implementation
///
/// The current algorithm is an introselect implementation based on [ipnsort] by Lukas Bergdoll
/// and Orson Peters, which is also the basis for [`sort_unstable`]. The fallback algorithm is
/// Median of Medians using Tukey's Ninther for pivot selection, which guarantees linear runtime
/// for all inputs.
///
/// [`sort_unstable`]: slice::sort_unstable
///
/// # Panics
///
/// Panics when `index >= len()`, and so always panics on empty slices.
///
/// May panic if `compare` does not implement a [total order].
///
/// # Examples
///
/// ```
/// let mut v = [-5i32, 4, 2, -3, 1];
///
/// // Find the items `>=` to the median, the median itself, and the items `<=` to it, by using
/// // a reversed comparator.
/// let (before, median, after) = v.select_nth_unstable_by(2, |a, b| b.cmp(a));
///
/// assert!(before == [4, 2] || before == [2, 4]);
/// assert_eq!(median, &mut 1);
/// assert!(after == [-3, -5] || after == [-5, -3]);
///
/// // We are only guaranteed the slice will be one of the following, based on the way we sort
/// // about the specified index.
/// assert!(v == [2, 4, 1, -5, -3] ||
/// v == [2, 4, 1, -3, -5] ||
/// v == [4, 2, 1, -5, -3] ||
/// v == [4, 2, 1, -3, -5]);
/// ```
///
/// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort
/// [total order]: https://en.wikipedia.org/wiki/Total_order
#[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
#[inline]
pub fn select_nth_unstable_by<F>(
&mut self,
index: usize,
mut compare: F,
) -> (&mut [T], &mut T, &mut [T])
where
F: FnMut(&T, &T) -> Ordering,
{
sort::select::partition_at_index(self, index, |a: &T, b: &T| compare(a, b) == Less)
}
/// Reorders the slice with a key extraction function such that the element at `index` is at a
/// sort-order position. All elements before `index` will have keys `<=` to the key at `index`,
/// and all elements after will have keys `>=` to it.
///
/// This reordering is unstable (i.e. any element that compares equal to the nth element may end
/// up at that position), in-place (i.e. does not allocate), and runs in *O*(*n*) time. This
/// function is also known as "kth element" in other libraries.
///
/// Returns a triple partitioning the reordered slice:
///
/// * The unsorted subslice before `index`, whose elements all satisfy `f(x) <= f(self[index])`.
///
/// * The element at `index`.
///
/// * The unsorted subslice after `index`, whose elements all satisfy `f(x) >= f(self[index])`.
///
/// # Current implementation
///
/// The current algorithm is an introselect implementation based on [ipnsort] by Lukas Bergdoll
/// and Orson Peters, which is also the basis for [`sort_unstable`]. The fallback algorithm is
/// Median of Medians using Tukey's Ninther for pivot selection, which guarantees linear runtime
/// for all inputs.
///
/// [`sort_unstable`]: slice::sort_unstable
///
/// # Panics
///
/// Panics when `index >= len()`, meaning it always panics on empty slices.
///
/// May panic if `K: Ord` does not implement a total order.
///
/// # Examples
///
/// ```
/// let mut v = [-5i32, 4, 1, -3, 2];
///
/// // Find the items `<=` to the absolute median, the absolute median itself, and the items
/// // `>=` to it.
/// let (lesser, median, greater) = v.select_nth_unstable_by_key(2, |a| a.abs());
///
/// assert!(lesser == [1, 2] || lesser == [2, 1]);
/// assert_eq!(median, &mut -3);
/// assert!(greater == [4, -5] || greater == [-5, 4]);
///
/// // We are only guaranteed the slice will be one of the following, based on the way we sort
/// // about the specified index.
/// assert!(v == [1, 2, -3, 4, -5] ||
/// v == [1, 2, -3, -5, 4] ||
/// v == [2, 1, -3, 4, -5] ||
/// v == [2, 1, -3, -5, 4]);
/// ```
///
/// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort
/// [total order]: https://en.wikipedia.org/wiki/Total_order
#[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
#[inline]
pub fn select_nth_unstable_by_key<K, F>(
&mut self,
index: usize,
mut f: F,
) -> (&mut [T], &mut T, &mut [T])
where
F: FnMut(&T) -> K,
K: Ord,
{
sort::select::partition_at_index(self, index, |a: &T, b: &T| f(a).lt(&f(b)))
}
/// Moves all consecutive repeated elements to the end of the slice according to the
/// [`PartialEq`] trait implementation.
///
/// Returns two slices. The first contains no consecutive repeated elements.
/// The second contains all the duplicates in no specified order.
///
/// If the slice is sorted, the first returned slice contains no duplicates.
///
/// # Examples
///
/// ```
/// #![feature(slice_partition_dedup)]
///
/// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
///
/// let (dedup, duplicates) = slice.partition_dedup();
///
/// assert_eq!(dedup, [1, 2, 3, 2, 1]);
/// assert_eq!(duplicates, [2, 3, 1]);
/// ```
#[unstable(feature = "slice_partition_dedup", issue = "54279")]
#[inline]
pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
where
T: PartialEq,
{
self.partition_dedup_by(|a, b| a == b)
}
/// Moves all but the first of consecutive elements to the end of the slice that are
/// "equal" according to the given predicate function.
///
/// Returns two slices. The first contains no consecutive repeated elements.
/// The second contains all the duplicates in no specified order.
///
/// The predicate `same_bucket(x, p)` is passed references to two elements from
/// the slice and must determine if the elements compare equal. The element `p` occurs
/// *before* `x` in the slice (`[.., p, .., x, ..]`), so `same_bucket(x, p)`
/// is receiving them in reversed order.
///
/// If the slice is sorted, the first returned slice contains no duplicates. For more
/// complicated predicates however, the order (ascending vs. descending) can matter.
///
/// Both references passed to `same_bucket` are mutable.
/// This allows merged elements in the first slice by mutating `p` and returning `true`.
///
/// # Examples
///
/// ```
/// #![feature(slice_partition_dedup)]
///
/// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
///
/// let (dedup, duplicates) = slice.partition_dedup_by(|x, p| x.eq_ignore_ascii_case(p));
///
/// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
/// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
/// ```
#[unstable(feature = "slice_partition_dedup", issue = "54279")]
#[inline]
pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
where
F: FnMut(&mut T, &mut T) -> bool,
{
// Although we have a mutable reference to `self`, we cannot make
// *arbitrary* changes. The `same_bucket` calls could panic, so we
// must ensure that the slice is in a valid state at all times.
//
// The way that we handle this is by using swaps; we iterate
// over all the elements, swapping as we go so that at the end
// the elements we wish to keep are in the front, and those we
// wish to reject are at the back. We can then split the slice.
// This operation is still `O(n)`.
//
// Example: We start in this state, where `r` represents "next
// read" and `w` represents "next_write".
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 1 | 2 | 3 | 3 |
// +---+---+---+---+---+---+
// w
//
// Comparing self[r] against self[w-1], this is not a duplicate, so
// we swap self[r] and self[w] (no effect as r==w) and then increment both
// r and w, leaving us with:
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 1 | 2 | 3 | 3 |
// +---+---+---+---+---+---+
// w
//
// Comparing self[r] against self[w-1], this value is a duplicate,
// so we increment `r` but leave everything else unchanged:
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 1 | 2 | 3 | 3 |
// +---+---+---+---+---+---+
// w
//
// Comparing self[r] against self[w-1], this is not a duplicate,
// so swap self[r] and self[w] and advance r and w:
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 2 | 1 | 3 | 3 |
// +---+---+---+---+---+---+
// w
//
// Not a duplicate, repeat:
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 2 | 3 | 1 | 3 |
// +---+---+---+---+---+---+
// w
//
// Duplicate, advance r. End of slice. Split at w.
let len = self.len();
if len <= 1 {
return (self, &mut []);
}
let ptr = self.as_mut_ptr();
let mut next_read: usize = 1;
let mut next_write: usize = 1;
// SAFETY: the `while` condition guarantees `next_read` and `next_write`
// are less than `len`, thus are inside `self`. `prev_ptr_write` points to
// one element before `ptr_write`, but `next_write` starts at 1, so
// `prev_ptr_write` is never less than 0 and is inside the slice.
// This fulfills the requirements for dereferencing `ptr_read`, `prev_ptr_write`
// and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
// and `prev_ptr_write.offset(1)`.
//
// `next_write` is also incremented at most once per loop at most meaning
// no element is skipped when it may need to be swapped.
//
// `ptr_read` and `prev_ptr_write` never point to the same element. This
// is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
// The explanation is simply that `next_read >= next_write` is always true,
// thus `next_read > next_write - 1` is too.
unsafe {
// Avoid bounds checks by using raw pointers.
while next_read < len {
let ptr_read = ptr.add(next_read);
let prev_ptr_write = ptr.add(next_write - 1);
if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
if next_read != next_write {
let ptr_write = prev_ptr_write.add(1);
mem::swap(&mut *ptr_read, &mut *ptr_write);
}
next_write += 1;
}
next_read += 1;
}
}
self.split_at_mut(next_write)
}
/// Moves all but the first of consecutive elements to the end of the slice that resolve
/// to the same key.
///
/// Returns two slices. The first contains no consecutive repeated elements.
/// The second contains all the duplicates in no specified order.
///
/// If the slice is sorted, the first returned slice contains no duplicates.
///
/// # Examples
///
/// ```
/// #![feature(slice_partition_dedup)]
///
/// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
///
/// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
///
/// assert_eq!(dedup, [10, 20, 30, 20, 11]);
/// assert_eq!(duplicates, [21, 30, 13]);
/// ```
#[unstable(feature = "slice_partition_dedup", issue = "54279")]
#[inline]
pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
where
F: FnMut(&mut T) -> K,
K: PartialEq,
{
self.partition_dedup_by(|a, b| key(a) == key(b))
}
/// Rotates the slice in-place such that the first `mid` elements of the
/// slice move to the end while the last `self.len() - mid` elements move to
/// the front.
///
/// After calling `rotate_left`, the element previously at index `mid` will
/// become the first element in the slice.
///
/// # Panics
///
/// This function will panic if `mid` is greater than the length of the
/// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
/// rotation.
///
/// # Complexity
///
/// Takes linear (in `self.len()`) time.
///
/// # Examples
///
/// ```
/// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
/// a.rotate_left(2);
/// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
/// ```
///
/// Rotating a subslice:
///
/// ```
/// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
/// a[1..5].rotate_left(1);
/// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
/// ```
#[stable(feature = "slice_rotate", since = "1.26.0")]
#[rustc_const_stable(feature = "const_slice_rotate", since = "1.92.0")]
pub const fn rotate_left(&mut self, mid: usize) {
assert!(mid <= self.len());
let k = self.len() - mid;
let p = self.as_mut_ptr();
// SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
// valid for reading and writing, as required by `ptr_rotate`.
unsafe {
rotate::ptr_rotate(mid, p.add(mid), k);
}
}
/// Rotates the slice in-place such that the first `self.len() - k`
/// elements of the slice move to the end while the last `k` elements move
/// to the front.
///
/// After calling `rotate_right`, the element previously at index
/// `self.len() - k` will become the first element in the slice.
///
/// # Panics
///
/// This function will panic if `k` is greater than the length of the
/// slice. Note that `k == self.len()` does _not_ panic and is a no-op
/// rotation.
///
/// # Complexity
///
/// Takes linear (in `self.len()`) time.
///
/// # Examples
///
/// ```
/// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
/// a.rotate_right(2);
/// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
/// ```
///
/// Rotating a subslice:
///
/// ```
/// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
/// a[1..5].rotate_right(1);
/// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
/// ```
#[stable(feature = "slice_rotate", since = "1.26.0")]
#[rustc_const_stable(feature = "const_slice_rotate", since = "1.92.0")]
pub const fn rotate_right(&mut self, k: usize) {
assert!(k <= self.len());
let mid = self.len() - k;
let p = self.as_mut_ptr();
// SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
// valid for reading and writing, as required by `ptr_rotate`.
unsafe {
rotate::ptr_rotate(mid, p.add(mid), k);
}
}
/// Moves the elements of this slice `N` places to the left, returning the ones
/// that "fall off" the front, and putting `inserted` at the end.
///
/// Equivalently, you can think of concatenating `self` and `inserted` into one
/// long sequence, then returning the left-most `N` items and the rest into `self`:
///
/// ```text
/// self (before) inserted
/// vvvvvvvvvvvvvvv vvv
/// [1, 2, 3, 4, 5] [9]
/// ↙ ↙ ↙ ↙ ↙ ↙
/// [1] [2, 3, 4, 5, 9]
/// ^^^ ^^^^^^^^^^^^^^^
/// returned self (after)
/// ```
///
/// See also [`Self::shift_right`] and compare [`Self::rotate_left`].
///
/// # Examples
///
/// ```
/// #![feature(slice_shift)]
///
/// // Same as the diagram above
/// let mut a = [1, 2, 3, 4, 5];
/// let inserted = [9];
/// let returned = a.shift_left(inserted);
/// assert_eq!(returned, [1]);
/// assert_eq!(a, [2, 3, 4, 5, 9]);
///
/// // You can shift multiple items at a time
/// let mut a = *b"Hello world";
/// assert_eq!(a.shift_left(*b" peace"), *b"Hello ");
/// assert_eq!(a, *b"world peace");
///
/// // The name comes from this operation's similarity to bitshifts
/// let mut a: u8 = 0b10010110;
/// a <<= 3;
/// assert_eq!(a, 0b10110000_u8);
/// let mut a: [_; 8] = [1, 0, 0, 1, 0, 1, 1, 0];
/// a.shift_left([0; 3]);
/// assert_eq!(a, [1, 0, 1, 1, 0, 0, 0, 0]);
///
/// // Remember you can sub-slice to affect less that the whole slice.
/// // For example, this is similar to `.remove(1)` + `.insert(4, 'Z')`
/// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
/// assert_eq!(a[1..=4].shift_left(['Z']), ['b']);
/// assert_eq!(a, ['a', 'c', 'd', 'e', 'Z', 'f']);
///
/// // If the size matches it's equivalent to `mem::replace`
/// let mut a = [1, 2, 3];
/// assert_eq!(a.shift_left([7, 8, 9]), [1, 2, 3]);
/// assert_eq!(a, [7, 8, 9]);
///
/// // Some of the "inserted" elements end up returned if the slice is too short
/// let mut a = [];
/// assert_eq!(a.shift_left([1, 2, 3]), [1, 2, 3]);
/// let mut a = [9];
/// assert_eq!(a.shift_left([1, 2, 3]), [9, 1, 2]);
/// assert_eq!(a, [3]);
/// ```
#[unstable(feature = "slice_shift", issue = "151772")]
pub const fn shift_left<const N: usize>(&mut self, inserted: [T; N]) -> [T; N] {
if let Some(shift) = self.len().checked_sub(N) {
// SAFETY: Having just checked that the inserted/returned arrays are
// shorter than (or the same length as) the slice:
// 1. The read for the items to return is in-bounds
// 2. We can `memmove` the slice over to cover the items we're returning
// to ensure those aren't double-dropped
// 3. Then we write (in-bounds for the same reason as the read) the
// inserted items atop the items of the slice that we just duplicated
//
// And none of this can panic, so there's no risk of intermediate unwinds.
unsafe {
let ptr = self.as_mut_ptr();
let returned = ptr.cast_array::<N>().read();
ptr.copy_from(ptr.add(N), shift);
ptr.add(shift).cast_array::<N>().write(inserted);
returned
}
} else {
// SAFETY: Having checked that the slice is strictly shorter than the
// inserted/returned arrays, it means we'll be copying the whole slice
// into the returned array, but that's not enough on its own. We also
// need to copy some of the inserted array into the returned array,
// with the rest going into the slice. Because `&mut` is exclusive
// and we own both `inserted` and `returned`, they're all disjoint
// allocations from each other as we can use `nonoverlapping` copies.
//
// We avoid double-frees by `ManuallyDrop`ing the inserted items,
// since we always copy them to other locations that will drop them
// instead. Plus nothing in here can panic -- it's just memcpy three
// times -- so there's no intermediate unwinds to worry about.
unsafe {
let len = self.len();
let slice = self.as_mut_ptr();
let inserted = mem::ManuallyDrop::new(inserted);
let inserted = (&raw const inserted).cast::<T>();
let mut returned = MaybeUninit::<[T; N]>::uninit();
let ptr = returned.as_mut_ptr().cast::<T>();
ptr.copy_from_nonoverlapping(slice, len);
ptr.add(len).copy_from_nonoverlapping(inserted, N - len);
slice.copy_from_nonoverlapping(inserted.add(N - len), len);
returned.assume_init()
}
}
}
/// Moves the elements of this slice `N` places to the right, returning the ones
/// that "fall off" the back, and putting `inserted` at the beginning.
///
/// Equivalently, you can think of concatenating `inserted` and `self` into one
/// long sequence, then returning the right-most `N` items and the rest into `self`:
///
/// ```text
/// inserted self (before)
/// vvv vvvvvvvvvvvvvvv
/// [0] [5, 6, 7, 8, 9]
/// ↘ ↘ ↘ ↘ ↘ ↘
/// [0, 5, 6, 7, 8] [9]
/// ^^^^^^^^^^^^^^^ ^^^
/// self (after) returned
/// ```
///
/// See also [`Self::shift_left`] and compare [`Self::rotate_right`].
///
/// # Examples
///
/// ```
/// #![feature(slice_shift)]
///
/// // Same as the diagram above
/// let mut a = [5, 6, 7, 8, 9];
/// let inserted = [0];
/// let returned = a.shift_right(inserted);
/// assert_eq!(returned, [9]);
/// assert_eq!(a, [0, 5, 6, 7, 8]);
///
/// // The name comes from this operation's similarity to bitshifts
/// let mut a: u8 = 0b10010110;
/// a >>= 3;
/// assert_eq!(a, 0b00010010_u8);
/// let mut a: [_; 8] = [1, 0, 0, 1, 0, 1, 1, 0];
/// a.shift_right([0; 3]);
/// assert_eq!(a, [0, 0, 0, 1, 0, 0, 1, 0]);
///
/// // Remember you can sub-slice to affect less that the whole slice.
/// // For example, this is similar to `.remove(4)` + `.insert(1, 'Z')`
/// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
/// assert_eq!(a[1..=4].shift_right(['Z']), ['e']);
/// assert_eq!(a, ['a', 'Z', 'b', 'c', 'd', 'f']);
///
/// // If the size matches it's equivalent to `mem::replace`
/// let mut a = [1, 2, 3];
/// assert_eq!(a.shift_right([7, 8, 9]), [1, 2, 3]);
/// assert_eq!(a, [7, 8, 9]);
///
/// // Some of the "inserted" elements end up returned if the slice is too short
/// let mut a = [];
/// assert_eq!(a.shift_right([1, 2, 3]), [1, 2, 3]);
/// let mut a = [9];
/// assert_eq!(a.shift_right([1, 2, 3]), [2, 3, 9]);
/// assert_eq!(a, [1]);
/// ```
#[unstable(feature = "slice_shift", issue = "151772")]
pub const fn shift_right<const N: usize>(&mut self, inserted: [T; N]) -> [T; N] {
if let Some(shift) = self.len().checked_sub(N) {
// SAFETY: Having just checked that the inserted/returned arrays are
// shorter than (or the same length as) the slice:
// 1. The read for the items to return is in-bounds
// 2. We can `memmove` the slice over to cover the items we're returning
// to ensure those aren't double-dropped
// 3. Then we write (in-bounds for the same reason as the read) the
// inserted items atop the items of the slice that we just duplicated
//
// And none of this can panic, so there's no risk of intermediate unwinds.
unsafe {
let ptr = self.as_mut_ptr();
let returned = ptr.add(shift).cast_array::<N>().read();
ptr.add(N).copy_from(ptr, shift);
ptr.cast_array::<N>().write(inserted);
returned
}
} else {
// SAFETY: Having checked that the slice is strictly shorter than the
// inserted/returned arrays, it means we'll be copying the whole slice
// into the returned array, but that's not enough on its own. We also
// need to copy some of the inserted array into the returned array,
// with the rest going into the slice. Because `&mut` is exclusive
// and we own both `inserted` and `returned`, they're all disjoint
// allocations from each other as we can use `nonoverlapping` copies.
//
// We avoid double-frees by `ManuallyDrop`ing the inserted items,
// since we always copy them to other locations that will drop them
// instead. Plus nothing in here can panic -- it's just memcpy three
// times -- so there's no intermediate unwinds to worry about.
unsafe {
let len = self.len();
let slice = self.as_mut_ptr();
let inserted = mem::ManuallyDrop::new(inserted);
let inserted = (&raw const inserted).cast::<T>();
let mut returned = MaybeUninit::<[T; N]>::uninit();
let ptr = returned.as_mut_ptr().cast::<T>();
ptr.add(N - len).copy_from_nonoverlapping(slice, len);
ptr.copy_from_nonoverlapping(inserted.add(len), N - len);
slice.copy_from_nonoverlapping(inserted, len);
returned.assume_init()
}
}
}
/// Fills `self` with elements by cloning `value`.
///
/// # Examples
///
/// ```
/// let mut buf = vec![0; 10];
/// buf.fill(1);
/// assert_eq!(buf, vec![1; 10]);
/// ```
#[doc(alias = "memset")]
#[stable(feature = "slice_fill", since = "1.50.0")]
pub fn fill(&mut self, value: T)
where
T: Clone,
{
specialize::SpecFill::spec_fill(self, value);
}
/// Fills `self` with elements returned by calling a closure repeatedly.
///
/// This method uses a closure to create new values. If you'd rather
/// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
/// trait to generate values, you can pass [`Default::default`] as the
/// argument.
///
/// [`fill`]: slice::fill
///
/// # Examples
///
/// ```
/// let mut buf = vec![1; 10];
/// buf.fill_with(Default::default);
/// assert_eq!(buf, vec![0; 10]);
/// ```
#[stable(feature = "slice_fill_with", since = "1.51.0")]
pub fn fill_with<F>(&mut self, mut f: F)
where
F: FnMut() -> T,
{
for el in self {
*el = f();
}
}
/// Copies the elements from `src` into `self`.
///
/// The length of `src` must be the same as `self`.
///
/// # Panics
///
/// This function will panic if the two slices have different lengths.
///
/// # Examples
///
/// Cloning two elements from a slice into another:
///
/// ```
/// let src = [1, 2, 3, 4];
/// let mut dst = [0, 0];
///
/// // Because the slices have to be the same length,
/// // we slice the source slice from four elements
/// // to two. It will panic if we don't do this.
/// dst.clone_from_slice(&src[2..]);
///
/// assert_eq!(src, [1, 2, 3, 4]);
/// assert_eq!(dst, [3, 4]);
/// ```
///
/// Rust enforces that there can only be one mutable reference with no
/// immutable references to a particular piece of data in a particular
/// scope. Because of this, attempting to use `clone_from_slice` on a
/// single slice will result in a compile failure:
///
/// ```compile_fail
/// let mut slice = [1, 2, 3, 4, 5];
///
/// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
/// ```
///
/// To work around this, we can use [`split_at_mut`] to create two distinct
/// sub-slices from a slice:
///
/// ```
/// let mut slice = [1, 2, 3, 4, 5];
///
/// {
/// let (left, right) = slice.split_at_mut(2);
/// left.clone_from_slice(&right[1..]);
/// }
///
/// assert_eq!(slice, [4, 5, 3, 4, 5]);
/// ```
///
/// [`copy_from_slice`]: slice::copy_from_slice
/// [`split_at_mut`]: slice::split_at_mut
#[stable(feature = "clone_from_slice", since = "1.7.0")]
#[track_caller]
#[rustc_const_unstable(feature = "const_clone", issue = "142757")]
pub const fn clone_from_slice(&mut self, src: &[T])
where
T: [const] Clone + [const] Destruct,
{
self.spec_clone_from(src);
}
/// Copies all elements from `src` into `self`, using a memcpy.
///
/// The length of `src` must be the same as `self`.
///
/// If `T` does not implement `Copy`, use [`clone_from_slice`].
///
/// # Panics
///
/// This function will panic if the two slices have different lengths.
///
/// # Examples
///
/// Copying two elements from a slice into another:
///
/// ```
/// let src = [1, 2, 3, 4];
/// let mut dst = [0, 0];
///
/// // Because the slices have to be the same length,
/// // we slice the source slice from four elements
/// // to two. It will panic if we don't do this.
/// dst.copy_from_slice(&src[2..]);
///
/// assert_eq!(src, [1, 2, 3, 4]);
/// assert_eq!(dst, [3, 4]);
/// ```
///
/// Rust enforces that there can only be one mutable reference with no
/// immutable references to a particular piece of data in a particular
/// scope. Because of this, attempting to use `copy_from_slice` on a
/// single slice will result in a compile failure:
///
/// ```compile_fail
/// let mut slice = [1, 2, 3, 4, 5];
///
/// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
/// ```
///
/// To work around this, we can use [`split_at_mut`] to create two distinct
/// sub-slices from a slice:
///
/// ```
/// let mut slice = [1, 2, 3, 4, 5];
///
/// {
/// let (left, right) = slice.split_at_mut(2);
/// left.copy_from_slice(&right[1..]);
/// }
///
/// assert_eq!(slice, [4, 5, 3, 4, 5]);
/// ```
///
/// [`clone_from_slice`]: slice::clone_from_slice
/// [`split_at_mut`]: slice::split_at_mut
#[doc(alias = "memcpy")]
#[inline]
#[stable(feature = "copy_from_slice", since = "1.9.0")]
#[rustc_const_stable(feature = "const_copy_from_slice", since = "1.87.0")]
#[track_caller]
pub const fn copy_from_slice(&mut self, src: &[T])
where
T: Copy,
{
// SAFETY: `T` implements `Copy`.
unsafe { copy_from_slice_impl(self, src) }
}
/// Copies elements from one part of the slice to another part of itself,
/// using a memmove.
///
/// `src` is the range within `self` to copy from. `dest` is the starting
/// index of the range within `self` to copy to, which will have the same
/// length as `src`. The two ranges may overlap. The ends of the two ranges
/// must be less than or equal to `self.len()`.
///
/// # Panics
///
/// This function will panic if either range exceeds the end of the slice,
/// or if the end of `src` is before the start.
///
/// # Examples
///
/// Copying four bytes within a slice:
///
/// ```
/// let mut bytes = *b"Hello, World!";
///
/// bytes.copy_within(1..5, 8);
///
/// assert_eq!(&bytes, b"Hello, Wello!");
/// ```
#[inline]
#[stable(feature = "copy_within", since = "1.37.0")]
#[track_caller]
pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
where
T: Copy,
{
let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
let count = src_end - src_start;
assert!(dest <= self.len() - count, "dest is out of bounds");
// SAFETY: the conditions for `ptr::copy` have all been checked above,
// as have those for `ptr::add`.
unsafe {
// Derive both `src_ptr` and `dest_ptr` from the same loan
let ptr = self.as_mut_ptr();
let src_ptr = ptr.add(src_start);
let dest_ptr = ptr.add(dest);
ptr::copy(src_ptr, dest_ptr, count);
}
}
/// Swaps all elements in `self` with those in `other`.
///
/// The length of `other` must be the same as `self`.
///
/// # Panics
///
/// This function will panic if the two slices have different lengths.
///
/// # Example
///
/// Swapping two elements across slices:
///
/// ```
/// let mut slice1 = [0, 0];
/// let mut slice2 = [1, 2, 3, 4];
///
/// slice1.swap_with_slice(&mut slice2[2..]);
///
/// assert_eq!(slice1, [3, 4]);
/// assert_eq!(slice2, [1, 2, 0, 0]);
/// ```
///
/// Rust enforces that there can only be one mutable reference to a
/// particular piece of data in a particular scope. Because of this,
/// attempting to use `swap_with_slice` on a single slice will result in
/// a compile failure:
///
/// ```compile_fail
/// let mut slice = [1, 2, 3, 4, 5];
/// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
/// ```
///
/// To work around this, we can use [`split_at_mut`] to create two distinct
/// mutable sub-slices from a slice:
///
/// ```
/// let mut slice = [1, 2, 3, 4, 5];
///
/// {
/// let (left, right) = slice.split_at_mut(2);
/// left.swap_with_slice(&mut right[1..]);
/// }
///
/// assert_eq!(slice, [4, 5, 3, 1, 2]);
/// ```
///
/// [`split_at_mut`]: slice::split_at_mut
#[stable(feature = "swap_with_slice", since = "1.27.0")]
#[rustc_const_unstable(feature = "const_swap_with_slice", issue = "142204")]
#[track_caller]
pub const fn swap_with_slice(&mut self, other: &mut [T]) {
assert!(self.len() == other.len(), "destination and source slices have different lengths");
// SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
// checked to have the same length. The slices cannot overlap because
// mutable references are exclusive.
unsafe {
ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
}
}
/// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
fn align_to_offsets<U>(&self) -> (usize, usize) {
// What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
// lowest number of `T`s. And how many `T`s we need for each such "multiple".
//
// Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
// for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
// place of every 3 Ts in the `rest` slice. A bit more complicated.
//
// Formula to calculate this is:
//
// Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
// Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
//
// Expanded and simplified:
//
// Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
// Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
//
// Luckily since all this is constant-evaluated... performance here matters not!
const fn gcd(a: usize, b: usize) -> usize {
if b == 0 { a } else { gcd(b, a % b) }
}
// Explicitly wrap the function call in a const block so it gets
// constant-evaluated even in debug mode.
let gcd: usize = const { gcd(size_of::<T>(), size_of::<U>()) };
let ts: usize = size_of::<U>() / gcd;
let us: usize = size_of::<T>() / gcd;
// Armed with this knowledge, we can find how many `U`s we can fit!
let us_len = self.len() / ts * us;
// And how many `T`s will be in the trailing slice!
let ts_len = self.len() % ts;
(us_len, ts_len)
}
/// Transmutes the slice to a slice of another type, ensuring alignment of the types is
/// maintained.
///
/// This method splits the slice into three distinct slices: prefix, correctly aligned middle
/// slice of a new type, and the suffix slice. The middle part will be as big as possible under
/// the given alignment constraint and element size.
///
/// This method has no purpose when either input element `T` or output element `U` are
/// zero-sized and will return the original slice without splitting anything.
///
/// # Safety
///
/// This method is essentially a `transmute` with respect to the elements in the returned
/// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// unsafe {
/// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
/// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
/// // less_efficient_algorithm_for_bytes(prefix);
/// // more_efficient_algorithm_for_aligned_shorts(shorts);
/// // less_efficient_algorithm_for_bytes(suffix);
/// }
/// ```
#[stable(feature = "slice_align_to", since = "1.30.0")]
#[must_use]
pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
// Note that most of this function will be constant-evaluated,
if U::IS_ZST || T::IS_ZST {
// handle ZSTs specially, which is – don't handle them at all.
return (self, &[], &[]);
}
// First, find at what point do we split between the first and 2nd slice. Easy with
// ptr.align_offset.
let ptr = self.as_ptr();
// SAFETY: See the `align_to_mut` method for the detailed safety comment.
let offset = unsafe { crate::ptr::align_offset(ptr, align_of::<U>()) };
if offset > self.len() {
(self, &[], &[])
} else {
let (left, rest) = self.split_at(offset);
let (us_len, ts_len) = rest.align_to_offsets::<U>();
// Inform Miri that we want to consider the "middle" pointer to be suitably aligned.
#[cfg(miri)]
crate::intrinsics::miri_promise_symbolic_alignment(
rest.as_ptr().cast(),
align_of::<U>(),
);
// SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
// since the caller guarantees that we can transmute `T` to `U` safely.
unsafe {
(
left,
from_raw_parts(rest.as_ptr() as *const U, us_len),
from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
)
}
}
}
/// Transmutes the mutable slice to a mutable slice of another type, ensuring alignment of the
/// types is maintained.
///
/// This method splits the slice into three distinct slices: prefix, correctly aligned middle
/// slice of a new type, and the suffix slice. The middle part will be as big as possible under
/// the given alignment constraint and element size.
///
/// This method has no purpose when either input element `T` or output element `U` are
/// zero-sized and will return the original slice without splitting anything.
///
/// # Safety
///
/// This method is essentially a `transmute` with respect to the elements in the returned
/// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// unsafe {
/// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
/// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
/// // less_efficient_algorithm_for_bytes(prefix);
/// // more_efficient_algorithm_for_aligned_shorts(shorts);
/// // less_efficient_algorithm_for_bytes(suffix);
/// }
/// ```
#[stable(feature = "slice_align_to", since = "1.30.0")]
#[must_use]
pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
// Note that most of this function will be constant-evaluated,
if U::IS_ZST || T::IS_ZST {
// handle ZSTs specially, which is – don't handle them at all.
return (self, &mut [], &mut []);
}
// First, find at what point do we split between the first and 2nd slice. Easy with
// ptr.align_offset.
let ptr = self.as_ptr();
// SAFETY: Here we are ensuring we will use aligned pointers for U for the
// rest of the method. This is done by passing a pointer to &[T] with an
// alignment targeted for U.
// `crate::ptr::align_offset` is called with a correctly aligned and
// valid pointer `ptr` (it comes from a reference to `self`) and with
// a size that is a power of two (since it comes from the alignment for U),
// satisfying its safety constraints.
let offset = unsafe { crate::ptr::align_offset(ptr, align_of::<U>()) };
if offset > self.len() {
(self, &mut [], &mut [])
} else {
let (left, rest) = self.split_at_mut(offset);
let (us_len, ts_len) = rest.align_to_offsets::<U>();
let rest_len = rest.len();
let mut_ptr = rest.as_mut_ptr();
// Inform Miri that we want to consider the "middle" pointer to be suitably aligned.
#[cfg(miri)]
crate::intrinsics::miri_promise_symbolic_alignment(
mut_ptr.cast() as *const (),
align_of::<U>(),
);
// We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
// SAFETY: see comments for `align_to`.
unsafe {
(
left,
from_raw_parts_mut(mut_ptr as *mut U, us_len),
from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
)
}
}
}
/// Splits a slice into a prefix, a middle of aligned SIMD types, and a suffix.
///
/// This is a safe wrapper around [`slice::align_to`], so inherits the same
/// guarantees as that method.
///
/// # Panics
///
/// This will panic if the size of the SIMD type is different from
/// `LANES` times that of the scalar.
///
/// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
/// that from ever happening, as only power-of-two numbers of lanes are
/// supported. It's possible that, in the future, those restrictions might
/// be lifted in a way that would make it possible to see panics from this
/// method for something like `LANES == 3`.
///
/// # Examples
///
/// ```
/// #![feature(portable_simd)]
/// use core::simd::prelude::*;
///
/// let short = &[1, 2, 3];
/// let (prefix, middle, suffix) = short.as_simd::<4>();
/// assert_eq!(middle, []); // Not enough elements for anything in the middle
///
/// // They might be split in any possible way between prefix and suffix
/// let it = prefix.iter().chain(suffix).copied();
/// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
///
/// fn basic_simd_sum(x: &[f32]) -> f32 {
/// use std::ops::Add;
/// let (prefix, middle, suffix) = x.as_simd();
/// let sums = f32x4::from_array([
/// prefix.iter().copied().sum(),
/// 0.0,
/// 0.0,
/// suffix.iter().copied().sum(),
/// ]);
/// let sums = middle.iter().copied().fold(sums, f32x4::add);
/// sums.reduce_sum()
/// }
///
/// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
/// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);
/// ```
#[unstable(feature = "portable_simd", issue = "86656")]
#[must_use]
pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])
where
Simd<T, LANES>: AsRef<[T; LANES]>,
T: simd::SimdElement,
{
// These are expected to always match, as vector types are laid out like
// arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
// might as well double-check since it'll optimize away anyhow.
assert_eq!(size_of::<Simd<T, LANES>>(), size_of::<[T; LANES]>());
// SAFETY: The simd types have the same layout as arrays, just with
// potentially-higher alignment, so the de-facto transmutes are sound.
unsafe { self.align_to() }
}
/// Splits a mutable slice into a mutable prefix, a middle of aligned SIMD types,
/// and a mutable suffix.
///
/// This is a safe wrapper around [`slice::align_to_mut`], so inherits the same
/// guarantees as that method.
///
/// This is the mutable version of [`slice::as_simd`]; see that for examples.
///
/// # Panics
///
/// This will panic if the size of the SIMD type is different from
/// `LANES` times that of the scalar.
///
/// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
/// that from ever happening, as only power-of-two numbers of lanes are
/// supported. It's possible that, in the future, those restrictions might
/// be lifted in a way that would make it possible to see panics from this
/// method for something like `LANES == 3`.
#[unstable(feature = "portable_simd", issue = "86656")]
#[must_use]
pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])
where
Simd<T, LANES>: AsMut<[T; LANES]>,
T: simd::SimdElement,
{
// These are expected to always match, as vector types are laid out like
// arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
// might as well double-check since it'll optimize away anyhow.
assert_eq!(size_of::<Simd<T, LANES>>(), size_of::<[T; LANES]>());
// SAFETY: The simd types have the same layout as arrays, just with
// potentially-higher alignment, so the de-facto transmutes are sound.
unsafe { self.align_to_mut() }
}
/// Checks if the elements of this slice are sorted.
///
/// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
/// slice yields exactly zero or one element, `true` is returned.
///
/// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
/// implies that this function returns `false` if any two consecutive items are not
/// comparable.
///
/// # Examples
///
/// ```
/// let empty: [i32; 0] = [];
///
/// assert!([1, 2, 2, 9].is_sorted());
/// assert!(![1, 3, 2, 4].is_sorted());
/// assert!([0].is_sorted());
/// assert!(empty.is_sorted());
/// assert!(![0.0, 1.0, f32::NAN].is_sorted());
/// ```
#[inline]
#[stable(feature = "is_sorted", since = "1.82.0")]
#[must_use]
pub fn is_sorted(&self) -> bool
where
T: PartialOrd,
{
// This odd number works the best. 32 + 1 extra due to overlapping chunk boundaries.
const CHUNK_SIZE: usize = 33;
if self.len() < CHUNK_SIZE {
return self.windows(2).all(|w| w[0] <= w[1]);
}
let mut i = 0;
// Check in chunks for autovectorization.
while i < self.len() - CHUNK_SIZE {
let chunk = &self[i..i + CHUNK_SIZE];
if !chunk.windows(2).fold(true, |acc, w| acc & (w[0] <= w[1])) {
return false;
}
// We need to ensure that chunk boundaries are also sorted.
// Overlap the next chunk with the last element of our last chunk.
i += CHUNK_SIZE - 1;
}
self[i..].windows(2).all(|w| w[0] <= w[1])
}
/// Checks if the elements of this slice are sorted using the given comparator function.
///
/// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
/// function to determine whether two elements are to be considered in sorted order.
///
/// # Examples
///
/// ```
/// assert!([1, 2, 2, 9].is_sorted_by(|a, b| a <= b));
/// assert!(![1, 2, 2, 9].is_sorted_by(|a, b| a < b));
///
/// assert!([0].is_sorted_by(|a, b| true));
/// assert!([0].is_sorted_by(|a, b| false));
///
/// let empty: [i32; 0] = [];
/// assert!(empty.is_sorted_by(|a, b| false));
/// assert!(empty.is_sorted_by(|a, b| true));
/// ```
#[stable(feature = "is_sorted", since = "1.82.0")]
#[must_use]
pub fn is_sorted_by<'a, F>(&'a self, mut compare: F) -> bool
where
F: FnMut(&'a T, &'a T) -> bool,
{
self.array_windows().all(|[a, b]| compare(a, b))
}
/// Checks if the elements of this slice are sorted using the given key extraction function.
///
/// Instead of comparing the slice's elements directly, this function compares the keys of the
/// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
/// documentation for more information.
///
/// [`is_sorted`]: slice::is_sorted
///
/// # Examples
///
/// ```
/// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
/// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
/// ```
#[inline]
#[stable(feature = "is_sorted", since = "1.82.0")]
#[must_use]
pub fn is_sorted_by_key<'a, F, K>(&'a self, f: F) -> bool
where
F: FnMut(&'a T) -> K,
K: PartialOrd,
{
self.iter().is_sorted_by_key(f)
}
/// Returns the index of the partition point according to the given predicate
/// (the index of the first element of the second partition).
///
/// The slice is assumed to be partitioned according to the given predicate.
/// This means that all elements for which the predicate returns true are at the start of the slice
/// and all elements for which the predicate returns false are at the end.
/// For example, `[7, 15, 3, 5, 4, 12, 6]` is partitioned under the predicate `x % 2 != 0`
/// (all odd numbers are at the start, all even at the end).
///
/// If this slice is not partitioned, the returned result is unspecified and meaningless,
/// as this method performs a kind of binary search.
///
/// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
///
/// [`binary_search`]: slice::binary_search
/// [`binary_search_by`]: slice::binary_search_by
/// [`binary_search_by_key`]: slice::binary_search_by_key
///
/// # Examples
///
/// ```
/// let v = [1, 2, 3, 3, 5, 6, 7];
/// let i = v.partition_point(|&x| x < 5);
///
/// assert_eq!(i, 4);
/// assert!(v[..i].iter().all(|&x| x < 5));
/// assert!(v[i..].iter().all(|&x| !(x < 5)));
/// ```
///
/// If all elements of the slice match the predicate, including if the slice
/// is empty, then the length of the slice will be returned:
///
/// ```
/// let a = [2, 4, 8];
/// assert_eq!(a.partition_point(|x| x < &100), a.len());
/// let a: [i32; 0] = [];
/// assert_eq!(a.partition_point(|x| x < &100), 0);
/// ```
///
/// If you want to insert an item to a sorted vector, while maintaining
/// sort order:
///
/// ```
/// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
/// let num = 42;
/// let idx = s.partition_point(|&x| x <= num);
/// s.insert(idx, num);
/// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
/// ```
#[rustc_const_unstable(feature = "const_binary_search", issue = "159532")]
#[stable(feature = "partition_point", since = "1.52.0")]
#[must_use]
pub const fn partition_point<P>(&self, mut pred: P) -> usize
where
P: [const] FnMut(&T) -> bool + [const] Destruct,
{
self.binary_search_by(const |x| if pred(x) { Less } else { Greater })
.unwrap_or_else(const |i| i)
}
/// Removes the subslice corresponding to the given range
/// and returns a reference to it.
///
/// Returns `None` and does not modify the slice if the given
/// range is out of bounds.
///
/// Note that this method only accepts one-sided ranges such as
/// `2..` or `..6`, but not `2..6`.
///
/// # Examples
///
/// Splitting off the first three elements of a slice:
///
/// ```
/// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
/// let mut first_three = slice.split_off(..3).unwrap();
///
/// assert_eq!(slice, &['d']);
/// assert_eq!(first_three, &['a', 'b', 'c']);
/// ```
///
/// Splitting off a slice starting with the third element:
///
/// ```
/// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
/// let mut tail = slice.split_off(2..).unwrap();
///
/// assert_eq!(slice, &['a', 'b']);
/// assert_eq!(tail, &['c', 'd']);
/// ```
///
/// Getting `None` when `range` is out of bounds:
///
/// ```
/// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
///
/// assert_eq!(None, slice.split_off(5..));
/// assert_eq!(None, slice.split_off(..5));
/// assert_eq!(None, slice.split_off(..=4));
/// let expected: &[char] = &['a', 'b', 'c', 'd'];
/// assert_eq!(Some(expected), slice.split_off(..4));
/// ```
#[inline]
#[must_use = "method does not modify the slice if the range is out of bounds"]
#[stable(feature = "slice_take", since = "1.87.0")]
pub fn split_off<'a, R: OneSidedRange<usize>>(
self: &mut &'a Self,
range: R,
) -> Option<&'a Self> {
let (direction, split_index) = split_point_of(range)?;
if split_index > self.len() {
return None;
}
let (front, back) = self.split_at(split_index);
match direction {
Direction::Front => {
*self = back;
Some(front)
}
Direction::Back => {
*self = front;
Some(back)
}
}
}
/// Removes the subslice corresponding to the given range
/// and returns a mutable reference to it.
///
/// Returns `None` and does not modify the slice if the given
/// range is out of bounds.
///
/// Note that this method only accepts one-sided ranges such as
/// `2..` or `..6`, but not `2..6`.
///
/// # Examples
///
/// Splitting off the first three elements of a slice:
///
/// ```
/// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
/// let mut first_three = slice.split_off_mut(..3).unwrap();
///
/// assert_eq!(slice, &mut ['d']);
/// assert_eq!(first_three, &mut ['a', 'b', 'c']);
/// ```
///
/// Splitting off a slice starting with the third element:
///
/// ```
/// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
/// let mut tail = slice.split_off_mut(2..).unwrap();
///
/// assert_eq!(slice, &mut ['a', 'b']);
/// assert_eq!(tail, &mut ['c', 'd']);
/// ```
///
/// Getting `None` when `range` is out of bounds:
///
/// ```
/// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
///
/// assert_eq!(None, slice.split_off_mut(5..));
/// assert_eq!(None, slice.split_off_mut(..5));
/// assert_eq!(None, slice.split_off_mut(..=4));
/// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
/// assert_eq!(Some(expected), slice.split_off_mut(..4));
/// ```
#[inline]
#[must_use = "method does not modify the slice if the range is out of bounds"]
#[stable(feature = "slice_take", since = "1.87.0")]
pub fn split_off_mut<'a, R: OneSidedRange<usize>>(
self: &mut &'a mut Self,
range: R,
) -> Option<&'a mut Self> {
let (direction, split_index) = split_point_of(range)?;
if split_index > self.len() {
return None;
}
let (front, back) = mem::take(self).split_at_mut(split_index);
match direction {
Direction::Front => {
*self = back;
Some(front)
}
Direction::Back => {
*self = front;
Some(back)
}
}
}
/// Removes the first element of the slice and returns a reference
/// to it.
///
/// Returns `None` if the slice is empty.
///
/// # Examples
///
/// ```
/// let mut slice: &[_] = &['a', 'b', 'c'];
/// let first = slice.split_off_first().unwrap();
///
/// assert_eq!(slice, &['b', 'c']);
/// assert_eq!(first, &'a');
/// ```
#[inline]
#[stable(feature = "slice_take", since = "1.87.0")]
#[rustc_const_unstable(feature = "const_split_off_first_last", issue = "138539")]
pub const fn split_off_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
// FIXME(const-hack): Use `?` when available in const instead of `let-else`.
let Some((first, rem)) = self.split_first() else { return None };
*self = rem;
Some(first)
}
/// Removes the first element of the slice and returns a mutable
/// reference to it.
///
/// Returns `None` if the slice is empty.
///
/// # Examples
///
/// ```
/// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
/// let first = slice.split_off_first_mut().unwrap();
/// *first = 'd';
///
/// assert_eq!(slice, &['b', 'c']);
/// assert_eq!(first, &'d');
/// ```
#[inline]
#[stable(feature = "slice_take", since = "1.87.0")]
#[rustc_const_unstable(feature = "const_split_off_first_last", issue = "138539")]
pub const fn split_off_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
// FIXME(const-hack): Use `mem::take` and `?` when available in const.
// Original: `mem::take(self).split_first_mut()?`
let Some((first, rem)) = mem::replace(self, &mut []).split_first_mut() else { return None };
*self = rem;
Some(first)
}
/// Removes the last element of the slice and returns a reference
/// to it.
///
/// Returns `None` if the slice is empty.
///
/// # Examples
///
/// ```
/// let mut slice: &[_] = &['a', 'b', 'c'];
/// let last = slice.split_off_last().unwrap();
///
/// assert_eq!(slice, &['a', 'b']);
/// assert_eq!(last, &'c');
/// ```
#[inline]
#[stable(feature = "slice_take", since = "1.87.0")]
#[rustc_const_unstable(feature = "const_split_off_first_last", issue = "138539")]
pub const fn split_off_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
// FIXME(const-hack): Use `?` when available in const instead of `let-else`.
let Some((last, rem)) = self.split_last() else { return None };
*self = rem;
Some(last)
}
/// Removes the last element of the slice and returns a mutable
/// reference to it.
///
/// Returns `None` if the slice is empty.
///
/// # Examples
///
/// ```
/// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
/// let last = slice.split_off_last_mut().unwrap();
/// *last = 'd';
///
/// assert_eq!(slice, &['a', 'b']);
/// assert_eq!(last, &'d');
/// ```
#[inline]
#[stable(feature = "slice_take", since = "1.87.0")]
#[rustc_const_unstable(feature = "const_split_off_first_last", issue = "138539")]
pub const fn split_off_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
// FIXME(const-hack): Use `mem::take` and `?` when available in const.
// Original: `mem::take(self).split_last_mut()?`
let Some((last, rem)) = mem::replace(self, &mut []).split_last_mut() else { return None };
*self = rem;
Some(last)
}
/// Returns mutable references to many indices at once, without doing any checks.
///
/// An index can be either a `usize`, a [`Range`] or a [`RangeInclusive`]. Note
/// that this method takes an array, so all indices must be of the same type.
/// If passed an array of `usize`s this method gives back an array of mutable references
/// to single elements, while if passed an array of ranges it gives back an array of
/// mutable references to slices.
///
/// For a safe alternative see [`get_disjoint_mut`].
///
/// # Safety
///
/// Calling this method with overlapping or out-of-bounds indices is *[undefined behavior]*
/// even if the resulting references are not used.
///
/// # Examples
///
/// ```
/// let x = &mut [1, 2, 4];
///
/// unsafe {
/// let [a, b] = x.get_disjoint_unchecked_mut([0, 2]);
/// *a *= 10;
/// *b *= 100;
/// }
/// assert_eq!(x, &[10, 2, 400]);
///
/// unsafe {
/// let [a, b] = x.get_disjoint_unchecked_mut([0..1, 1..3]);
/// a[0] = 8;
/// b[0] = 88;
/// b[1] = 888;
/// }
/// assert_eq!(x, &[8, 88, 888]);
///
/// unsafe {
/// let [a, b] = x.get_disjoint_unchecked_mut([1..=2, 0..=0]);
/// a[0] = 11;
/// a[1] = 111;
/// b[0] = 1;
/// }
/// assert_eq!(x, &[1, 11, 111]);
/// ```
///
/// [`get_disjoint_mut`]: slice::get_disjoint_mut
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
#[stable(feature = "get_many_mut", since = "1.86.0")]
#[inline]
#[track_caller]
pub unsafe fn get_disjoint_unchecked_mut<I, const N: usize>(
&mut self,
indices: [I; N],
) -> [&mut I::Output; N]
where
I: GetDisjointMutIndex + SliceIndex<Self>,
{
// NB: This implementation is written as it is because any variation of
// `indices.map(|i| self.get_unchecked_mut(i))` would make miri unhappy,
// or generate worse code otherwise. This is also why we need to go
// through a raw pointer here.
let slice: *mut [T] = self;
let mut arr: MaybeUninit<[&mut I::Output; N]> = MaybeUninit::uninit();
let arr_ptr = arr.as_mut_ptr();
// SAFETY: We expect `indices` to contain disjunct values that are
// in bounds of `self`.
unsafe {
for i in 0..N {
let idx = indices.get_unchecked(i).clone();
arr_ptr.cast::<&mut I::Output>().add(i).write(&mut *slice.get_unchecked_mut(idx));
}
arr.assume_init()
}
}
/// Returns mutable references to many indices at once.
///
/// An index can be either a `usize`, a [`Range`] or a [`RangeInclusive`]. Note
/// that this method takes an array, so all indices must be of the same type.
/// If passed an array of `usize`s this method gives back an array of mutable references
/// to single elements, while if passed an array of ranges it gives back an array of
/// mutable references to slices.
///
/// Returns an error if any index is out-of-bounds, or if there are overlapping indices.
/// An empty range is not considered to overlap if it is located at the beginning or at
/// the end of another range, but is considered to overlap if it is located in the middle.
///
/// This method does a O(n^2) check to check that there are no overlapping indices, so be careful
/// when passing many indices.
///
/// # Examples
///
/// ```
/// let v = &mut [1, 2, 3];
/// if let Ok([a, b]) = v.get_disjoint_mut([0, 2]) {
/// *a = 413;
/// *b = 612;
/// }
/// assert_eq!(v, &[413, 2, 612]);
///
/// if let Ok([a, b]) = v.get_disjoint_mut([0..1, 1..3]) {
/// a[0] = 8;
/// b[0] = 88;
/// b[1] = 888;
/// }
/// assert_eq!(v, &[8, 88, 888]);
///
/// if let Ok([a, b]) = v.get_disjoint_mut([1..=2, 0..=0]) {
/// a[0] = 11;
/// a[1] = 111;
/// b[0] = 1;
/// }
/// assert_eq!(v, &[1, 11, 111]);
/// ```
#[stable(feature = "get_many_mut", since = "1.86.0")]
#[inline]
pub fn get_disjoint_mut<I, const N: usize>(
&mut self,
indices: [I; N],
) -> Result<[&mut I::Output; N], GetDisjointMutError>
where
I: GetDisjointMutIndex + SliceIndex<Self>,
{
get_disjoint_check_valid(&indices, self.len())?;
// SAFETY: The `get_disjoint_check_valid()` call checked that all indices
// are disjunct and in bounds.
unsafe { Ok(self.get_disjoint_unchecked_mut(indices)) }
}
/// Returns the index that an element reference points to.
///
/// Returns `None` if `element` does not point to the start of an element within the slice.
///
/// This method is useful for extending slice iterators like [`slice::split`].
///
/// Note that this uses pointer arithmetic and **does not compare elements**.
/// To find the index of an element via comparison, use
/// [`.iter().position()`](crate::iter::Iterator::position) instead.
///
/// # Panics
/// Panics if `T` is zero-sized.
///
/// # Examples
/// Basic usage:
/// ```
/// let nums: &[u32] = &[1, 7, 1, 1];
/// let num = &nums[2];
///
/// assert_eq!(num, &1);
/// assert_eq!(nums.element_offset(num), Some(2));
/// ```
/// Returning `None` with an unaligned element:
/// ```
/// let arr: &[[u32; 2]] = &[[0, 1], [2, 3]];
/// let flat_arr: &[u32] = arr.as_flattened();
///
/// let ok_elm: &[u32; 2] = flat_arr[0..2].try_into().unwrap();
/// let weird_elm: &[u32; 2] = flat_arr[1..3].try_into().unwrap();
///
/// assert_eq!(ok_elm, &[0, 1]);
/// assert_eq!(weird_elm, &[1, 2]);
///
/// assert_eq!(arr.element_offset(ok_elm), Some(0)); // Points to element 0
/// assert_eq!(arr.element_offset(weird_elm), None); // Points between element 0 and 1
/// ```
#[must_use]
#[stable(feature = "element_offset", since = "1.94.0")]
pub fn element_offset(&self, element: &T) -> Option<usize> {
if T::IS_ZST {
panic!("elements are zero-sized");
}
let self_start = self.as_ptr().addr();
let elem_start = ptr::from_ref(element).addr();
let byte_offset = elem_start.wrapping_sub(self_start);
if !byte_offset.is_multiple_of(size_of::<T>()) {
return None;
}
let offset = byte_offset / size_of::<T>();
if offset < self.len() { Some(offset) } else { None }
}
/// Returns the range of indices that a subslice points to.
///
/// Returns `None` if `subslice` does not point within the slice or if it is not aligned with the
/// elements in the slice.
///
/// This method **does not compare elements**. Instead, this method finds the location in the slice that
/// `subslice` was obtained from. To find the index of a subslice via comparison, instead use
/// [`.windows()`](slice::windows)[`.position()`](crate::iter::Iterator::position).
///
/// This method is useful for extending slice iterators like [`slice::split`].
///
/// Note that this may return a false positive (either `Some(0..0)` or `Some(self.len()..self.len())`)
/// if `subslice` has a length of zero and points to the beginning or end of another, separate, slice.
///
/// # Panics
/// Panics if `T` is zero-sized.
///
/// # Examples
/// Basic usage:
/// ```
/// use core::range::Range;
///
/// let nums = &[0, 5, 10, 0, 0, 5];
///
/// let mut iter = nums
/// .split(|t| *t == 0)
/// .map(|n| nums.subslice_range(n).unwrap());
///
/// assert_eq!(iter.next(), Some(Range { start: 0, end: 0 }));
/// assert_eq!(iter.next(), Some(Range { start: 1, end: 3 }));
/// assert_eq!(iter.next(), Some(Range { start: 4, end: 4 }));
/// assert_eq!(iter.next(), Some(Range { start: 5, end: 6 }));
/// ```
#[must_use]
#[stable(feature = "substr_range", since = "1.98.0")]
pub fn subslice_range(&self, subslice: &[T]) -> Option<core::range::Range<usize>> {
if T::IS_ZST {
panic!("elements are zero-sized");
}
let self_start = self.as_ptr().addr();
let subslice_start = subslice.as_ptr().addr();
let byte_start = subslice_start.wrapping_sub(self_start);
if !byte_start.is_multiple_of(size_of::<T>()) {
return None;
}
let start = byte_start / size_of::<T>();
let end = start.wrapping_add(subslice.len());
if start <= self.len() && end <= self.len() {
Some(core::range::Range { start, end })
} else {
None
}
}
/// Returns the same slice `&[T]`.
///
/// This method is redundant when used directly on `&[T]`, but
/// it helps dereferencing other "container" types to slices,
/// for example `Box<[T]>` or `Arc<[T]>`.
#[inline]
#[unstable(feature = "str_as_str", issue = "130366")]
pub const fn as_slice(&self) -> &[T] {
self
}
/// Returns the same slice `&mut [T]`.
///
/// This method is redundant when used directly on `&mut [T]`, but
/// it helps dereferencing other "container" types to slices,
/// for example `Box<[T]>` or `MutexGuard<[T]>`.
#[inline]
#[unstable(feature = "str_as_str", issue = "130366")]
pub const fn as_mut_slice(&mut self) -> &mut [T] {
self
}
}
impl<T> [MaybeUninit<T>] {
/// Transmutes the mutable uninitialized slice to a mutable uninitialized slice of
/// another type, ensuring alignment of the types is maintained.
///
/// This is a safe wrapper around [`slice::align_to_mut`], so inherits the same
/// guarantees as that method.
///
/// # Examples
///
/// ```
/// #![feature(align_to_uninit_mut)]
/// use std::mem::MaybeUninit;
///
/// pub struct BumpAllocator<'scope> {
/// memory: &'scope mut [MaybeUninit<u8>],
/// }
///
/// impl<'scope> BumpAllocator<'scope> {
/// pub fn new(memory: &'scope mut [MaybeUninit<u8>]) -> Self {
/// Self { memory }
/// }
/// pub fn try_alloc_uninit<T>(&mut self) -> Option<&'scope mut MaybeUninit<T>> {
/// let first_end = self.memory.as_ptr().align_offset(align_of::<T>()) + size_of::<T>();
/// let prefix = self.memory.split_off_mut(..first_end)?;
/// Some(&mut prefix.align_to_uninit_mut::<T>().1[0])
/// }
/// pub fn try_alloc_u32(&mut self, value: u32) -> Option<&'scope mut u32> {
/// let uninit = self.try_alloc_uninit()?;
/// Some(uninit.write(value))
/// }
/// }
///
/// let mut memory = [MaybeUninit::<u8>::uninit(); 10];
/// let mut allocator = BumpAllocator::new(&mut memory);
/// let v = allocator.try_alloc_u32(42);
/// assert_eq!(v, Some(&mut 42));
/// ```
#[unstable(feature = "align_to_uninit_mut", issue = "139062")]
#[inline]
#[must_use]
pub fn align_to_uninit_mut<U>(&mut self) -> (&mut Self, &mut [MaybeUninit<U>], &mut Self) {
// SAFETY: `MaybeUninit` is transparent. Correct size and alignment are guaranteed by
// `align_to_mut` itself. Therefore the only thing that we have to ensure for a safe
// `transmute` is that the values are valid for the types involved. But for `MaybeUninit`
// any values are valid, so this operation is safe.
unsafe { self.align_to_mut() }
}
}
impl<T, const N: usize> [[T; N]] {
/// Takes a `&[[T; N]]`, and flattens it to a `&[T]`.
///
/// For the opposite operation, see [`as_chunks`] and [`as_rchunks`].
///
/// [`as_chunks`]: slice::as_chunks
/// [`as_rchunks`]: slice::as_rchunks
///
/// # Panics
///
/// This panics if the length of the resulting slice would overflow a `usize`.
///
/// This is only possible when flattening a slice of arrays of zero-sized
/// types, and thus tends to be irrelevant in practice. If
/// `size_of::<T>() > 0`, this will never panic.
///
/// # Examples
///
/// ```
/// assert_eq!([[1, 2, 3], [4, 5, 6]].as_flattened(), &[1, 2, 3, 4, 5, 6]);
///
/// assert_eq!(
/// [[1, 2, 3], [4, 5, 6]].as_flattened(),
/// [[1, 2], [3, 4], [5, 6]].as_flattened(),
/// );
///
/// let slice_of_empty_arrays: &[[i32; 0]] = &[[], [], [], [], []];
/// assert!(slice_of_empty_arrays.as_flattened().is_empty());
///
/// let empty_slice_of_arrays: &[[u32; 10]] = &[];
/// assert!(empty_slice_of_arrays.as_flattened().is_empty());
/// ```
#[stable(feature = "slice_flatten", since = "1.80.0")]
#[rustc_const_stable(feature = "const_slice_flatten", since = "1.87.0")]
pub const fn as_flattened(&self) -> &[T] {
let len = if T::IS_ZST {
self.len().checked_mul(N).expect("slice len overflow")
} else {
// SAFETY: `self.len() * N` cannot overflow because `self` is
// already in the address space.
unsafe { self.len().unchecked_mul(N) }
};
// SAFETY: `[T]` is layout-identical to `[T; N]`
unsafe { from_raw_parts(self.as_ptr().cast(), len) }
}
/// Takes a `&mut [[T; N]]`, and flattens it to a `&mut [T]`.
///
/// For the opposite operation, see [`as_chunks_mut`] and [`as_rchunks_mut`].
///
/// [`as_chunks_mut`]: slice::as_chunks_mut
/// [`as_rchunks_mut`]: slice::as_rchunks_mut
///
/// # Panics
///
/// This panics if the length of the resulting slice would overflow a `usize`.
///
/// This is only possible when flattening a slice of arrays of zero-sized
/// types, and thus tends to be irrelevant in practice. If
/// `size_of::<T>() > 0`, this will never panic.
///
/// # Examples
///
/// ```
/// fn add_5_to_all(slice: &mut [i32]) {
/// for i in slice {
/// *i += 5;
/// }
/// }
///
/// let mut array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
/// add_5_to_all(array.as_flattened_mut());
/// assert_eq!(array, [[6, 7, 8], [9, 10, 11], [12, 13, 14]]);
/// ```
#[stable(feature = "slice_flatten", since = "1.80.0")]
#[rustc_const_stable(feature = "const_slice_flatten", since = "1.87.0")]
pub const fn as_flattened_mut(&mut self) -> &mut [T] {
let len = if T::IS_ZST {
self.len().checked_mul(N).expect("slice len overflow")
} else {
// SAFETY: `self.len() * N` cannot overflow because `self` is
// already in the address space.
unsafe { self.len().unchecked_mul(N) }
};
// SAFETY: `[T]` is layout-identical to `[T; N]`
unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), len) }
}
}
impl [f32] {
/// Sorts the slice of floats.
///
/// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses
/// the ordering defined by [`f32::total_cmp`].
///
/// # Current implementation
///
/// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by).
///
/// # Examples
///
/// ```
/// #![feature(sort_floats)]
/// let mut v = [2.6, -5e-8, f32::NAN, 8.29, f32::INFINITY, -1.0, 0.0, -f32::INFINITY, -0.0];
///
/// v.sort_floats();
/// let sorted = [-f32::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f32::INFINITY, f32::NAN];
/// assert_eq!(&v[..8], &sorted[..8]);
/// assert!(v[8].is_nan());
/// ```
#[unstable(feature = "sort_floats", issue = "93396")]
#[inline]
pub fn sort_floats(&mut self) {
self.sort_unstable_by(f32::total_cmp);
}
}
impl [f64] {
/// Sorts the slice of floats.
///
/// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses
/// the ordering defined by [`f64::total_cmp`].
///
/// # Current implementation
///
/// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by).
///
/// # Examples
///
/// ```
/// #![feature(sort_floats)]
/// let mut v = [2.6, -5e-8, f64::NAN, 8.29, f64::INFINITY, -1.0, 0.0, -f64::INFINITY, -0.0];
///
/// v.sort_floats();
/// let sorted = [-f64::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f64::INFINITY, f64::NAN];
/// assert_eq!(&v[..8], &sorted[..8]);
/// assert!(v[8].is_nan());
/// ```
#[unstable(feature = "sort_floats", issue = "93396")]
#[inline]
pub fn sort_floats(&mut self) {
self.sort_unstable_by(f64::total_cmp);
}
}
/// Copies `src` to `dest`.
///
/// # Safety
/// `T` must implement one of `Copy` or `TrivialClone`.
#[track_caller]
const unsafe fn copy_from_slice_impl<T: Clone>(dest: &mut [T], src: &[T]) {
// The panic code path was put into a cold function to not bloat the
// call site.
#[cfg_attr(not(panic = "immediate-abort"), inline(never), cold)]
#[cfg_attr(panic = "immediate-abort", inline)]
#[track_caller]
const fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
const_panic!(
"copy_from_slice: source slice length does not match destination slice length",
"copy_from_slice: source slice length ({src_len}) does not match destination slice length ({dst_len})",
src_len: usize,
dst_len: usize,
)
}
if dest.len() != src.len() {
len_mismatch_fail(dest.len(), src.len());
}
// SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
// checked to have the same length. The slices cannot overlap because
// mutable references are exclusive.
unsafe {
ptr::copy_nonoverlapping(src.as_ptr(), dest.as_mut_ptr(), dest.len());
}
}
#[rustc_const_unstable(feature = "const_clone", issue = "142757")]
const trait CloneFromSpec<T> {
fn spec_clone_from(&mut self, src: &[T])
where
T: [const] Destruct;
}
#[rustc_const_unstable(feature = "const_clone", issue = "142757")]
const impl<T> CloneFromSpec<T> for [T]
where
T: [const] Clone + [const] Destruct,
{
#[track_caller]
default fn spec_clone_from(&mut self, src: &[T]) {
assert!(self.len() == src.len(), "destination and source slices have different lengths");
// NOTE: We need to explicitly slice them to the same length
// to make it easier for the optimizer to elide bounds checking.
// But since it can't be relied on we also have an explicit specialization for T: Copy.
let len = self.len();
let src = &src[..len];
// FIXME(const_hack): make this a `for idx in 0..self.len()` loop.
let mut idx = 0;
while idx < self.len() {
self[idx].clone_from(&src[idx]);
idx += 1;
}
}
}
#[rustc_const_unstable(feature = "const_clone", issue = "142757")]
const impl<T> CloneFromSpec<T> for [T]
where
T: [const] TrivialClone + [const] Destruct,
{
#[track_caller]
fn spec_clone_from(&mut self, src: &[T]) {
// SAFETY: `T` implements `TrivialClone`.
unsafe {
copy_from_slice_impl(self, src);
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_default", issue = "143894")]
const impl<T> Default for &[T] {
/// Creates an empty slice.
fn default() -> Self {
&[]
}
}
#[stable(feature = "mut_slice_default", since = "1.5.0")]
#[rustc_const_unstable(feature = "const_default", issue = "143894")]
const impl<T> Default for &mut [T] {
/// Creates a mutable empty slice.
fn default() -> Self {
&mut []
}
}
#[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
/// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
/// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
/// `str`) to slices, and then this trait will be replaced or abolished.
pub trait SlicePattern {
/// The element type of the slice being matched on.
type Item;
/// Currently, the consumers of `SlicePattern` need a slice.
fn as_slice(&self) -> &[Self::Item];
}
#[stable(feature = "slice_strip", since = "1.51.0")]
impl<T> SlicePattern for [T] {
type Item = T;
#[inline]
fn as_slice(&self) -> &[Self::Item] {
self
}
}
#[stable(feature = "slice_strip", since = "1.51.0")]
impl<T, const N: usize> SlicePattern for [T; N] {
type Item = T;
#[inline]
fn as_slice(&self) -> &[Self::Item] {
self
}
}
/// This checks every index against each other, and against `len`.
///
/// This will do `binomial(N + 1, 2) = N * (N + 1) / 2 = 0, 1, 3, 6, 10, ..`
/// comparison operations.
#[inline]
fn get_disjoint_check_valid<I: GetDisjointMutIndex, const N: usize>(
indices: &[I; N],
len: usize,
) -> Result<(), GetDisjointMutError> {
// NB: The optimizer should inline the loops into a sequence
// of instructions without additional branching.
for (i, idx) in indices.iter().enumerate() {
if !idx.is_in_bounds(len) {
return Err(GetDisjointMutError::IndexOutOfBounds);
}
for idx2 in &indices[..i] {
if idx.is_overlapping(idx2) {
return Err(GetDisjointMutError::OverlappingIndices);
}
}
}
Ok(())
}
/// The error type returned by [`get_disjoint_mut`][`slice::get_disjoint_mut`].
///
/// It indicates one of two possible errors:
/// - An index is out-of-bounds.
/// - The same index appeared multiple times in the array
/// (or different but overlapping indices when ranges are provided).
///
/// # Examples
///
/// ```
/// use std::slice::GetDisjointMutError;
///
/// let v = &mut [1, 2, 3];
/// assert_eq!(v.get_disjoint_mut([0, 999]), Err(GetDisjointMutError::IndexOutOfBounds));
/// assert_eq!(v.get_disjoint_mut([1, 1]), Err(GetDisjointMutError::OverlappingIndices));
/// ```
#[stable(feature = "get_many_mut", since = "1.86.0")]
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum GetDisjointMutError {
/// An index provided was out-of-bounds for the slice.
IndexOutOfBounds,
/// Two indices provided were overlapping.
OverlappingIndices,
}
#[stable(feature = "get_many_mut", since = "1.86.0")]
impl fmt::Display for GetDisjointMutError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let msg = match self {
GetDisjointMutError::IndexOutOfBounds => "an index is out of bounds",
GetDisjointMutError::OverlappingIndices => "there were overlapping indices",
};
fmt::Display::fmt(msg, f)
}
}
/// A helper trait for `<[T]>::get_disjoint_mut()`.
///
/// # Safety
///
/// If `is_in_bounds()` returns `true` and `is_overlapping()` returns `false`,
/// it must be safe to index the slice with the indices.
#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
pub impl(self) unsafe trait GetDisjointMutIndex: Clone {
/// Returns `true` if `self` is in bounds for `len` slice elements.
#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
fn is_in_bounds(&self, len: usize) -> bool;
/// Returns `true` if `self` overlaps with `other`.
///
/// Note that we don't consider zero-length ranges to overlap at the beginning or the end,
/// but do consider them to overlap in the middle.
#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
fn is_overlapping(&self, other: &Self) -> bool;
}
#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
// SAFETY: We implement `is_in_bounds()` and `is_overlapping()` correctly.
unsafe impl GetDisjointMutIndex for usize {
#[inline]
fn is_in_bounds(&self, len: usize) -> bool {
*self < len
}
#[inline]
fn is_overlapping(&self, other: &Self) -> bool {
*self == *other
}
}
#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
// SAFETY: We implement `is_in_bounds()` and `is_overlapping()` correctly.
unsafe impl GetDisjointMutIndex for Range<usize> {
#[inline]
fn is_in_bounds(&self, len: usize) -> bool {
(self.start <= self.end) & (self.end <= len)
}
#[inline]
fn is_overlapping(&self, other: &Self) -> bool {
(self.start < other.end) & (other.start < self.end)
}
}
#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
// SAFETY: We implement `is_in_bounds()` and `is_overlapping()` correctly.
unsafe impl GetDisjointMutIndex for RangeInclusive<usize> {
#[inline]
fn is_in_bounds(&self, len: usize) -> bool {
(self.start <= self.end) & (self.end < len)
}
#[inline]
fn is_overlapping(&self, other: &Self) -> bool {
(self.start <= other.end) & (other.start <= self.end)
}
}
#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
// SAFETY: We implement `is_in_bounds()` and `is_overlapping()` correctly.
unsafe impl GetDisjointMutIndex for range::Range<usize> {
#[inline]
fn is_in_bounds(&self, len: usize) -> bool {
Range::from(*self).is_in_bounds(len)
}
#[inline]
fn is_overlapping(&self, other: &Self) -> bool {
Range::from(*self).is_overlapping(&Range::from(*other))
}
}
#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
// SAFETY: We implement `is_in_bounds()` and `is_overlapping()` correctly.
unsafe impl GetDisjointMutIndex for range::RangeInclusive<usize> {
#[inline]
fn is_in_bounds(&self, len: usize) -> bool {
RangeInclusive::from(*self).is_in_bounds(len)
}
#[inline]
fn is_overlapping(&self, other: &Self) -> bool {
RangeInclusive::from(*self).is_overlapping(&RangeInclusive::from(*other))
}
}