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rust / rust-lang / rust / HEAD / . / library / alloc / src / string.rs
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//! A UTF-8–encoded, growable string.
//!
//! This module contains the [`String`] type, the [`ToString`] trait for
//! converting to strings, and several error types that may result from
//! working with [`String`]s.
//!
//! # Examples
//!
//! There are multiple ways to create a new [`String`] from a string literal:
//!
//! ```
//! let s = "Hello".to_string();
//!
//! let s = String::from("world");
//! let s: String = "also this".into();
//! ```
//!
//! You can create a new [`String`] from an existing one by concatenating with
//! `+`:
//!
//! ```
//! let s = "Hello".to_string();
//!
//! let message = s + " world!";
//! ```
//!
//! If you have a vector of valid UTF-8 bytes, you can make a [`String`] out of
//! it. You can do the reverse too.
//!
//! ```
//! let sparkle_heart = vec![240, 159, 146, 150];
//!
//! // We know these bytes are valid, so we'll use `unwrap()`.
//! let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
//!
//! assert_eq!("πŸ’–", sparkle_heart);
//!
//! let bytes = sparkle_heart.into_bytes();
//!
//! assert_eq!(bytes, [240, 159, 146, 150]);
//! ```
#![stable(feature = "rust1", since = "1.0.0")]
use core::error::Error;
use core::iter::FusedIterator;
#[cfg(not(no_global_oom_handling))]
use core::iter::from_fn;
#[cfg(not(no_global_oom_handling))]
use core::ops::Add;
#[cfg(not(no_global_oom_handling))]
use core::ops::AddAssign;
#[cfg(not(no_global_oom_handling))]
use core::ops::Bound::{Excluded, Included, Unbounded};
use core::ops::{self, Range, RangeBounds};
use core::str::pattern::{Pattern, Utf8Pattern};
use core::{fmt, hash, ptr, slice};
#[cfg(not(no_global_oom_handling))]
use crate::alloc::Allocator;
#[cfg(not(no_global_oom_handling))]
use crate::borrow::{Cow, ToOwned};
use crate::boxed::Box;
use crate::collections::TryReserveError;
use crate::str::{self, CharIndices, Chars, Utf8Error, from_utf8_unchecked_mut};
#[cfg(not(no_global_oom_handling))]
use crate::str::{FromStr, from_boxed_utf8_unchecked};
use crate::vec::{self, Vec};
/// A UTF-8–encoded, growable string.
///
/// `String` is the most common string type. It has ownership over the contents
/// of the string, stored in a heap-allocated buffer (see [Representation](#representation)).
/// It is closely related to its borrowed counterpart, the primitive [`str`].
///
/// # Examples
///
/// You can create a `String` from [a literal string][`&str`] with [`String::from`]:
///
/// [`String::from`]: From::from
///
/// ```
/// let hello = String::from("Hello, world!");
/// ```
///
/// You can append a [`char`] to a `String` with the [`push`] method, and
/// append a [`&str`] with the [`push_str`] method:
///
/// ```
/// let mut hello = String::from("Hello, ");
///
/// hello.push('w');
/// hello.push_str("orld!");
/// ```
///
/// [`push`]: String::push
/// [`push_str`]: String::push_str
///
/// If you have a vector of UTF-8 bytes, you can create a `String` from it with
/// the [`from_utf8`] method:
///
/// ```
/// // some bytes, in a vector
/// let sparkle_heart = vec![240, 159, 146, 150];
///
/// // We know these bytes are valid, so we'll use `unwrap()`.
/// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
///
/// assert_eq!("πŸ’–", sparkle_heart);
/// ```
///
/// [`from_utf8`]: String::from_utf8
///
/// # UTF-8
///
/// `String`s are always valid UTF-8. If you need a non-UTF-8 string, consider
/// [`OsString`]. It is similar, but without the UTF-8 constraint. Because UTF-8
/// is a variable width encoding, `String`s are typically smaller than an array of
/// the same `char`s:
///
/// ```
/// // `s` is ASCII which represents each `char` as one byte
/// let s = "hello";
/// assert_eq!(s.len(), 5);
///
/// // A `char` array with the same contents would be longer because
/// // every `char` is four bytes
/// let s = ['h', 'e', 'l', 'l', 'o'];
/// let size: usize = s.into_iter().map(|c| size_of_val(&c)).sum();
/// assert_eq!(size, 20);
///
/// // However, for non-ASCII strings, the difference will be smaller
/// // and sometimes they are the same
/// let s = "πŸ’–πŸ’–πŸ’–πŸ’–πŸ’–";
/// assert_eq!(s.len(), 20);
///
/// let s = ['πŸ’–', 'πŸ’–', 'πŸ’–', 'πŸ’–', 'πŸ’–'];
/// let size: usize = s.into_iter().map(|c| size_of_val(&c)).sum();
/// assert_eq!(size, 20);
/// ```
///
/// This raises interesting questions as to how `s[i]` should work.
/// What should `i` be here? Several options include byte indices and
/// `char` indices but, because of UTF-8 encoding, only byte indices
/// would provide constant time indexing. Getting the `i`th `char`, for
/// example, is available using [`chars`]:
///
/// ```
/// let s = "hello";
/// let third_character = s.chars().nth(2);
/// assert_eq!(third_character, Some('l'));
///
/// let s = "πŸ’–πŸ’–πŸ’–πŸ’–πŸ’–";
/// let third_character = s.chars().nth(2);
/// assert_eq!(third_character, Some('πŸ’–'));
/// ```
///
/// Next, what should `s[i]` return? Because indexing returns a reference
/// to underlying data it could be `&u8`, `&[u8]`, or something similar.
/// Since we're only providing one index, `&u8` makes the most sense but that
/// might not be what the user expects and can be explicitly achieved with
/// [`as_bytes()`]:
///
/// ```
/// // The first byte is 104 - the byte value of `'h'`
/// let s = "hello";
/// assert_eq!(s.as_bytes()[0], 104);
/// // or
/// assert_eq!(s.as_bytes()[0], b'h');
///
/// // The first byte is 240 which isn't obviously useful
/// let s = "πŸ’–πŸ’–πŸ’–πŸ’–πŸ’–";
/// assert_eq!(s.as_bytes()[0], 240);
/// ```
///
/// Due to these ambiguities/restrictions, indexing with a `usize` is simply
/// forbidden:
///
/// ```compile_fail,E0277
/// let s = "hello";
///
/// // The following will not compile!
/// println!("The first letter of s is {}", s[0]);
/// ```
///
/// It is more clear, however, how `&s[i..j]` should work (that is,
/// indexing with a range). It should accept byte indices (to be constant-time)
/// and return a `&str` which is UTF-8 encoded. This is also called "string slicing".
/// Note this will panic if the byte indices provided are not character
/// boundaries - see [`is_char_boundary`] for more details. See the implementations
/// for [`SliceIndex<str>`] for more details on string slicing. For a non-panicking
/// version of string slicing, see [`get`].
///
/// [`OsString`]: ../../std/ffi/struct.OsString.html "ffi::OsString"
/// [`SliceIndex<str>`]: core::slice::SliceIndex
/// [`as_bytes()`]: str::as_bytes
/// [`get`]: str::get
/// [`is_char_boundary`]: str::is_char_boundary
///
/// The [`bytes`] and [`chars`] methods return iterators over the bytes and
/// codepoints of the string, respectively. To iterate over codepoints along
/// with byte indices, use [`char_indices`].
///
/// [`bytes`]: str::bytes
/// [`chars`]: str::chars
/// [`char_indices`]: str::char_indices
///
/// # Deref
///
/// `String` implements <code>[Deref]<Target = [str]></code>, and so inherits all of [`str`]'s
/// methods. In addition, this means that you can pass a `String` to a
/// function which takes a [`&str`] by using an ampersand (`&`):
///
/// ```
/// fn takes_str(s: &str) { }
///
/// let s = String::from("Hello");
///
/// takes_str(&s);
/// ```
///
/// This will create a [`&str`] from the `String` and pass it in. This
/// conversion is very inexpensive, and so generally, functions will accept
/// [`&str`]s as arguments unless they need a `String` for some specific
/// reason.
///
/// In certain cases Rust doesn't have enough information to make this
/// conversion, known as [`Deref`] coercion. In the following example a string
/// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function
/// `example_func` takes anything that implements the trait. In this case Rust
/// would need to make two implicit conversions, which Rust doesn't have the
/// means to do. For that reason, the following example will not compile.
///
/// ```compile_fail,E0277
/// trait TraitExample {}
///
/// impl<'a> TraitExample for &'a str {}
///
/// fn example_func<A: TraitExample>(example_arg: A) {}
///
/// let example_string = String::from("example_string");
/// example_func(&example_string);
/// ```
///
/// There are two options that would work instead. The first would be to
/// change the line `example_func(&example_string);` to
/// `example_func(example_string.as_str());`, using the method [`as_str()`]
/// to explicitly extract the string slice containing the string. The second
/// way changes `example_func(&example_string);` to
/// `example_func(&*example_string);`. In this case we are dereferencing a
/// `String` to a [`str`], then referencing the [`str`] back to
/// [`&str`]. The second way is more idiomatic, however both work to do the
/// conversion explicitly rather than relying on the implicit conversion.
///
/// # Representation
///
/// A `String` is made up of three components: a pointer to some bytes, a
/// length, and a capacity. The pointer points to the internal buffer which `String`
/// uses to store its data. The length is the number of bytes currently stored
/// in the buffer, and the capacity is the size of the buffer in bytes. As such,
/// the length will always be less than or equal to the capacity.
///
/// This buffer is always stored on the heap.
///
/// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
/// methods:
///
// FIXME Update this when vec_into_raw_parts is stabilized
/// ```
/// use std::mem;
///
/// let story = String::from("Once upon a time...");
///
/// // Prevent automatically dropping the String's data
/// let mut story = mem::ManuallyDrop::new(story);
///
/// let ptr = story.as_mut_ptr();
/// let len = story.len();
/// let capacity = story.capacity();
///
/// // story has nineteen bytes
/// assert_eq!(19, len);
///
/// // We can re-build a String out of ptr, len, and capacity. This is all
/// // unsafe because we are responsible for making sure the components are
/// // valid:
/// let s = unsafe { String::from_raw_parts(ptr, len, capacity) } ;
///
/// assert_eq!(String::from("Once upon a time..."), s);
/// ```
///
/// [`as_ptr`]: str::as_ptr
/// [`len`]: String::len
/// [`capacity`]: String::capacity
///
/// If a `String` has enough capacity, adding elements to it will not
/// re-allocate. For example, consider this program:
///
/// ```
/// let mut s = String::new();
///
/// println!("{}", s.capacity());
///
/// for _ in 0..5 {
/// s.push_str("hello");
/// println!("{}", s.capacity());
/// }
/// ```
///
/// This will output the following:
///
/// ```text
/// 0
/// 8
/// 16
/// 16
/// 32
/// 32
/// ```
///
/// At first, we have no memory allocated at all, but as we append to the
/// string, it increases its capacity appropriately. If we instead use the
/// [`with_capacity`] method to allocate the correct capacity initially:
///
/// ```
/// let mut s = String::with_capacity(25);
///
/// println!("{}", s.capacity());
///
/// for _ in 0..5 {
/// s.push_str("hello");
/// println!("{}", s.capacity());
/// }
/// ```
///
/// [`with_capacity`]: String::with_capacity
///
/// We end up with a different output:
///
/// ```text
/// 25
/// 25
/// 25
/// 25
/// 25
/// 25
/// ```
///
/// Here, there's no need to allocate more memory inside the loop.
///
/// [str]: prim@str "str"
/// [`str`]: prim@str "str"
/// [`&str`]: prim@str "&str"
/// [Deref]: core::ops::Deref "ops::Deref"
/// [`Deref`]: core::ops::Deref "ops::Deref"
/// [`as_str()`]: String::as_str
#[derive(PartialEq, PartialOrd, Eq, Ord)]
#[stable(feature = "rust1", since = "1.0.0")]
#[lang = "String"]
pub struct String {
vec: Vec<u8>,
}
/// A possible error value when converting a `String` from a UTF-8 byte vector.
///
/// This type is the error type for the [`from_utf8`] method on [`String`]. It
/// is designed in such a way to carefully avoid reallocations: the
/// [`into_bytes`] method will give back the byte vector that was used in the
/// conversion attempt.
///
/// [`from_utf8`]: String::from_utf8
/// [`into_bytes`]: FromUtf8Error::into_bytes
///
/// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
/// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
/// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
/// through the [`utf8_error`] method.
///
/// [`Utf8Error`]: str::Utf8Error "std::str::Utf8Error"
/// [`std::str`]: core::str "std::str"
/// [`&str`]: prim@str "&str"
/// [`utf8_error`]: FromUtf8Error::utf8_error
///
/// # Examples
///
/// ```
/// // some invalid bytes, in a vector
/// let bytes = vec![0, 159];
///
/// let value = String::from_utf8(bytes);
///
/// assert!(value.is_err());
/// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[cfg_attr(not(no_global_oom_handling), derive(Clone))]
#[derive(Debug, PartialEq, Eq)]
pub struct FromUtf8Error {
bytes: Vec<u8>,
error: Utf8Error,
}
/// A possible error value when converting a `String` from a UTF-16 byte slice.
///
/// This type is the error type for the [`from_utf16`] method on [`String`].
///
/// [`from_utf16`]: String::from_utf16
///
/// # Examples
///
/// ```
/// // π„žmu<invalid>ic
/// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
/// 0xD800, 0x0069, 0x0063];
///
/// assert!(String::from_utf16(v).is_err());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Debug)]
pub struct FromUtf16Error(());
impl String {
/// Creates a new empty `String`.
///
/// Given that the `String` is empty, this will not allocate any initial
/// buffer. While that means that this initial operation is very
/// inexpensive, it may cause excessive allocation later when you add
/// data. If you have an idea of how much data the `String` will hold,
/// consider the [`with_capacity`] method to prevent excessive
/// re-allocation.
///
/// [`with_capacity`]: String::with_capacity
///
/// # Examples
///
/// ```
/// let s = String::new();
/// ```
#[inline]
#[rustc_const_stable(feature = "const_string_new", since = "1.39.0")]
#[rustc_diagnostic_item = "string_new"]
#[stable(feature = "rust1", since = "1.0.0")]
#[must_use]
pub const fn new() -> String {
String { vec: Vec::new() }
}
/// Creates a new empty `String` with at least the specified capacity.
///
/// `String`s have an internal buffer to hold their data. The capacity is
/// the length of that buffer, and can be queried with the [`capacity`]
/// method. This method creates an empty `String`, but one with an initial
/// buffer that can hold at least `capacity` bytes. This is useful when you
/// may be appending a bunch of data to the `String`, reducing the number of
/// reallocations it needs to do.
///
/// [`capacity`]: String::capacity
///
/// If the given capacity is `0`, no allocation will occur, and this method
/// is identical to the [`new`] method.
///
/// [`new`]: String::new
///
/// # Examples
///
/// ```
/// let mut s = String::with_capacity(10);
///
/// // The String contains no chars, even though it has capacity for more
/// assert_eq!(s.len(), 0);
///
/// // These are all done without reallocating...
/// let cap = s.capacity();
/// for _ in 0..10 {
/// s.push('a');
/// }
///
/// assert_eq!(s.capacity(), cap);
///
/// // ...but this may make the string reallocate
/// s.push('a');
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[must_use]
pub fn with_capacity(capacity: usize) -> String {
String { vec: Vec::with_capacity(capacity) }
}
/// Creates a new empty `String` with at least the specified capacity.
///
/// # Errors
///
/// Returns [`Err`] if the capacity exceeds `isize::MAX` bytes,
/// or if the memory allocator reports failure.
///
#[inline]
#[unstable(feature = "try_with_capacity", issue = "91913")]
pub fn try_with_capacity(capacity: usize) -> Result<String, TryReserveError> {
Ok(String { vec: Vec::try_with_capacity(capacity)? })
}
/// Converts a vector of bytes to a `String`.
///
/// A string ([`String`]) is made of bytes ([`u8`]), and a vector of bytes
/// ([`Vec<u8>`]) is made of bytes, so this function converts between the
/// two. Not all byte slices are valid `String`s, however: `String`
/// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
/// the bytes are valid UTF-8, and then does the conversion.
///
/// If you are sure that the byte slice is valid UTF-8, and you don't want
/// to incur the overhead of the validity check, there is an unsafe version
/// of this function, [`from_utf8_unchecked`], which has the same behavior
/// but skips the check.
///
/// This method will take care to not copy the vector, for efficiency's
/// sake.
///
/// If you need a [`&str`] instead of a `String`, consider
/// [`str::from_utf8`].
///
/// The inverse of this method is [`into_bytes`].
///
/// # Errors
///
/// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
/// provided bytes are not UTF-8. The vector you moved in is also included.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// // some bytes, in a vector
/// let sparkle_heart = vec![240, 159, 146, 150];
///
/// // We know these bytes are valid, so we'll use `unwrap()`.
/// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
///
/// assert_eq!("πŸ’–", sparkle_heart);
/// ```
///
/// Incorrect bytes:
///
/// ```
/// // some invalid bytes, in a vector
/// let sparkle_heart = vec![0, 159, 146, 150];
///
/// assert!(String::from_utf8(sparkle_heart).is_err());
/// ```
///
/// See the docs for [`FromUtf8Error`] for more details on what you can do
/// with this error.
///
/// [`from_utf8_unchecked`]: String::from_utf8_unchecked
/// [`Vec<u8>`]: crate::vec::Vec "Vec"
/// [`&str`]: prim@str "&str"
/// [`into_bytes`]: String::into_bytes
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_diagnostic_item = "string_from_utf8"]
pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
match str::from_utf8(&vec) {
Ok(..) => Ok(String { vec }),
Err(e) => Err(FromUtf8Error { bytes: vec, error: e }),
}
}
/// Converts a slice of bytes to a string, including invalid characters.
///
/// Strings are made of bytes ([`u8`]), and a slice of bytes
/// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
/// between the two. Not all byte slices are valid strings, however: strings
/// are required to be valid UTF-8. During this conversion,
/// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
/// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], which looks like this: οΏ½
///
/// [byteslice]: prim@slice
/// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
///
/// If you are sure that the byte slice is valid UTF-8, and you don't want
/// to incur the overhead of the conversion, there is an unsafe version
/// of this function, [`from_utf8_unchecked`], which has the same behavior
/// but skips the checks.
///
/// [`from_utf8_unchecked`]: String::from_utf8_unchecked
///
/// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
/// UTF-8, then we need to insert the replacement characters, which will
/// change the size of the string, and hence, require a `String`. But if
/// it's already valid UTF-8, we don't need a new allocation. This return
/// type allows us to handle both cases.
///
/// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// // some bytes, in a vector
/// let sparkle_heart = vec![240, 159, 146, 150];
///
/// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
///
/// assert_eq!("πŸ’–", sparkle_heart);
/// ```
///
/// Incorrect bytes:
///
/// ```
/// // some invalid bytes
/// let input = b"Hello \xF0\x90\x80World";
/// let output = String::from_utf8_lossy(input);
///
/// assert_eq!("Hello οΏ½World", output);
/// ```
#[must_use]
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn from_utf8_lossy(v: &[u8]) -> Cow<'_, str> {
let mut iter = v.utf8_chunks();
let first_valid = if let Some(chunk) = iter.next() {
let valid = chunk.valid();
if chunk.invalid().is_empty() {
debug_assert_eq!(valid.len(), v.len());
return Cow::Borrowed(valid);
}
valid
} else {
return Cow::Borrowed("");
};
const REPLACEMENT: &str = "\u{FFFD}";
let mut res = String::with_capacity(v.len());
res.push_str(first_valid);
res.push_str(REPLACEMENT);
for chunk in iter {
res.push_str(chunk.valid());
if !chunk.invalid().is_empty() {
res.push_str(REPLACEMENT);
}
}
Cow::Owned(res)
}
/// Converts a [`Vec<u8>`] to a `String`, substituting invalid UTF-8
/// sequences with replacement characters.
///
/// See [`from_utf8_lossy`] for more details.
///
/// [`from_utf8_lossy`]: String::from_utf8_lossy
///
/// Note that this function does not guarantee reuse of the original `Vec`
/// allocation.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(string_from_utf8_lossy_owned)]
/// // some bytes, in a vector
/// let sparkle_heart = vec![240, 159, 146, 150];
///
/// let sparkle_heart = String::from_utf8_lossy_owned(sparkle_heart);
///
/// assert_eq!(String::from("πŸ’–"), sparkle_heart);
/// ```
///
/// Incorrect bytes:
///
/// ```
/// #![feature(string_from_utf8_lossy_owned)]
/// // some invalid bytes
/// let input: Vec<u8> = b"Hello \xF0\x90\x80World".into();
/// let output = String::from_utf8_lossy_owned(input);
///
/// assert_eq!(String::from("Hello οΏ½World"), output);
/// ```
#[must_use]
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "string_from_utf8_lossy_owned", issue = "129436")]
pub fn from_utf8_lossy_owned(v: Vec<u8>) -> String {
if let Cow::Owned(string) = String::from_utf8_lossy(&v) {
string
} else {
// SAFETY: `String::from_utf8_lossy`'s contract ensures that if
// it returns a `Cow::Borrowed`, it is a valid UTF-8 string.
// Otherwise, it returns a new allocation of an owned `String`, with
// replacement characters for invalid sequences, which is returned
// above.
unsafe { String::from_utf8_unchecked(v) }
}
}
/// Decode a native endian UTF-16–encoded vector `v` into a `String`,
/// returning [`Err`] if `v` contains any invalid data.
///
/// # Examples
///
/// ```
/// // π„žmusic
/// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
/// 0x0073, 0x0069, 0x0063];
/// assert_eq!(String::from("π„žmusic"),
/// String::from_utf16(v).unwrap());
///
/// // π„žmu<invalid>ic
/// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
/// 0xD800, 0x0069, 0x0063];
/// assert!(String::from_utf16(v).is_err());
/// ```
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
// This isn't done via collect::<Result<_, _>>() for performance reasons.
// FIXME: the function can be simplified again when #48994 is closed.
let mut ret = String::with_capacity(v.len());
for c in char::decode_utf16(v.iter().cloned()) {
if let Ok(c) = c {
ret.push(c);
} else {
return Err(FromUtf16Error(()));
}
}
Ok(ret)
}
/// Decode a native endian UTF-16–encoded slice `v` into a `String`,
/// replacing invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
///
/// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
/// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
/// conversion requires a memory allocation.
///
/// [`from_utf8_lossy`]: String::from_utf8_lossy
/// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
/// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
///
/// # Examples
///
/// ```
/// // π„žmus<invalid>ic<invalid>
/// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
/// 0x0073, 0xDD1E, 0x0069, 0x0063,
/// 0xD834];
///
/// assert_eq!(String::from("π„žmus\u{FFFD}ic\u{FFFD}"),
/// String::from_utf16_lossy(v));
/// ```
#[cfg(not(no_global_oom_handling))]
#[must_use]
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn from_utf16_lossy(v: &[u16]) -> String {
char::decode_utf16(v.iter().cloned())
.map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
.collect()
}
/// Decode a UTF-16LE–encoded vector `v` into a `String`,
/// returning [`Err`] if `v` contains any invalid data.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(str_from_utf16_endian)]
/// // π„žmusic
/// let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
/// 0x73, 0x00, 0x69, 0x00, 0x63, 0x00];
/// assert_eq!(String::from("π„žmusic"),
/// String::from_utf16le(v).unwrap());
///
/// // π„žmu<invalid>ic
/// let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
/// 0x00, 0xD8, 0x69, 0x00, 0x63, 0x00];
/// assert!(String::from_utf16le(v).is_err());
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "str_from_utf16_endian", issue = "116258")]
pub fn from_utf16le(v: &[u8]) -> Result<String, FromUtf16Error> {
let (chunks, []) = v.as_chunks::<2>() else {
return Err(FromUtf16Error(()));
};
match (cfg!(target_endian = "little"), unsafe { v.align_to::<u16>() }) {
(true, ([], v, [])) => Self::from_utf16(v),
_ => char::decode_utf16(chunks.iter().copied().map(u16::from_le_bytes))
.collect::<Result<_, _>>()
.map_err(|_| FromUtf16Error(())),
}
}
/// Decode a UTF-16LE–encoded slice `v` into a `String`, replacing
/// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
///
/// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
/// `from_utf16le_lossy` returns a `String` since the UTF-16 to UTF-8
/// conversion requires a memory allocation.
///
/// [`from_utf8_lossy`]: String::from_utf8_lossy
/// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
/// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(str_from_utf16_endian)]
/// // π„žmus<invalid>ic<invalid>
/// let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
/// 0x73, 0x00, 0x1E, 0xDD, 0x69, 0x00, 0x63, 0x00,
/// 0x34, 0xD8];
///
/// assert_eq!(String::from("π„žmus\u{FFFD}ic\u{FFFD}"),
/// String::from_utf16le_lossy(v));
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "str_from_utf16_endian", issue = "116258")]
pub fn from_utf16le_lossy(v: &[u8]) -> String {
match (cfg!(target_endian = "little"), unsafe { v.align_to::<u16>() }) {
(true, ([], v, [])) => Self::from_utf16_lossy(v),
(true, ([], v, [_remainder])) => Self::from_utf16_lossy(v) + "\u{FFFD}",
_ => {
let (chunks, remainder) = v.as_chunks::<2>();
let string = char::decode_utf16(chunks.iter().copied().map(u16::from_le_bytes))
.map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
.collect();
if remainder.is_empty() { string } else { string + "\u{FFFD}" }
}
}
}
/// Decode a UTF-16BE–encoded vector `v` into a `String`,
/// returning [`Err`] if `v` contains any invalid data.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(str_from_utf16_endian)]
/// // π„žmusic
/// let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
/// 0x00, 0x73, 0x00, 0x69, 0x00, 0x63];
/// assert_eq!(String::from("π„žmusic"),
/// String::from_utf16be(v).unwrap());
///
/// // π„žmu<invalid>ic
/// let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
/// 0xD8, 0x00, 0x00, 0x69, 0x00, 0x63];
/// assert!(String::from_utf16be(v).is_err());
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "str_from_utf16_endian", issue = "116258")]
pub fn from_utf16be(v: &[u8]) -> Result<String, FromUtf16Error> {
let (chunks, []) = v.as_chunks::<2>() else {
return Err(FromUtf16Error(()));
};
match (cfg!(target_endian = "big"), unsafe { v.align_to::<u16>() }) {
(true, ([], v, [])) => Self::from_utf16(v),
_ => char::decode_utf16(chunks.iter().copied().map(u16::from_be_bytes))
.collect::<Result<_, _>>()
.map_err(|_| FromUtf16Error(())),
}
}
/// Decode a UTF-16BE–encoded slice `v` into a `String`, replacing
/// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
///
/// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
/// `from_utf16le_lossy` returns a `String` since the UTF-16 to UTF-8
/// conversion requires a memory allocation.
///
/// [`from_utf8_lossy`]: String::from_utf8_lossy
/// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
/// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(str_from_utf16_endian)]
/// // π„žmus<invalid>ic<invalid>
/// let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
/// 0x00, 0x73, 0xDD, 0x1E, 0x00, 0x69, 0x00, 0x63,
/// 0xD8, 0x34];
///
/// assert_eq!(String::from("π„žmus\u{FFFD}ic\u{FFFD}"),
/// String::from_utf16be_lossy(v));
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "str_from_utf16_endian", issue = "116258")]
pub fn from_utf16be_lossy(v: &[u8]) -> String {
match (cfg!(target_endian = "big"), unsafe { v.align_to::<u16>() }) {
(true, ([], v, [])) => Self::from_utf16_lossy(v),
(true, ([], v, [_remainder])) => Self::from_utf16_lossy(v) + "\u{FFFD}",
_ => {
let (chunks, remainder) = v.as_chunks::<2>();
let string = char::decode_utf16(chunks.iter().copied().map(u16::from_be_bytes))
.map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
.collect();
if remainder.is_empty() { string } else { string + "\u{FFFD}" }
}
}
}
/// Decomposes a `String` into its raw components: `(pointer, length, capacity)`.
///
/// Returns the raw pointer to the underlying data, the length of
/// the string (in bytes), and the allocated capacity of the data
/// (in bytes). These are the same arguments in the same order as
/// the arguments to [`from_raw_parts`].
///
/// After calling this function, the caller is responsible for the
/// memory previously managed by the `String`. The only way to do
/// this is to convert the raw pointer, length, and capacity back
/// into a `String` with the [`from_raw_parts`] function, allowing
/// the destructor to perform the cleanup.
///
/// [`from_raw_parts`]: String::from_raw_parts
///
/// # Examples
///
/// ```
/// #![feature(vec_into_raw_parts)]
/// let s = String::from("hello");
///
/// let (ptr, len, cap) = s.into_raw_parts();
///
/// let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
/// assert_eq!(rebuilt, "hello");
/// ```
#[must_use = "losing the pointer will leak memory"]
#[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
pub fn into_raw_parts(self) -> (*mut u8, usize, usize) {
self.vec.into_raw_parts()
}
/// Creates a new `String` from a pointer, a length and a capacity.
///
/// # Safety
///
/// This is highly unsafe, due to the number of invariants that aren't
/// checked:
///
/// * all safety requirements for [`Vec::<u8>::from_raw_parts`].
/// * all safety requirements for [`String::from_utf8_unchecked`].
///
/// Violating these may cause problems like corrupting the allocator's
/// internal data structures. For example, it is normally **not** safe to
/// build a `String` from a pointer to a C `char` array containing UTF-8
/// _unless_ you are certain that array was originally allocated by the
/// Rust standard library's allocator.
///
/// The ownership of `buf` is effectively transferred to the
/// `String` which may then deallocate, reallocate or change the
/// contents of memory pointed to by the pointer at will. Ensure
/// that nothing else uses the pointer after calling this
/// function.
///
/// # Examples
///
// FIXME Update this when vec_into_raw_parts is stabilized
/// ```
/// use std::mem;
///
/// unsafe {
/// let s = String::from("hello");
///
/// // Prevent automatically dropping the String's data
/// let mut s = mem::ManuallyDrop::new(s);
///
/// let ptr = s.as_mut_ptr();
/// let len = s.len();
/// let capacity = s.capacity();
///
/// let s = String::from_raw_parts(ptr, len, capacity);
///
/// assert_eq!(String::from("hello"), s);
/// }
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
unsafe { String { vec: Vec::from_raw_parts(buf, length, capacity) } }
}
/// Converts a vector of bytes to a `String` without checking that the
/// string contains valid UTF-8.
///
/// See the safe version, [`from_utf8`], for more details.
///
/// [`from_utf8`]: String::from_utf8
///
/// # Safety
///
/// This function is unsafe because it does not check that the bytes passed
/// to it are valid UTF-8. If this constraint is violated, it may cause
/// memory unsafety issues with future users of the `String`, as the rest of
/// the standard library assumes that `String`s are valid UTF-8.
///
/// # Examples
///
/// ```
/// // some bytes, in a vector
/// let sparkle_heart = vec![240, 159, 146, 150];
///
/// let sparkle_heart = unsafe {
/// String::from_utf8_unchecked(sparkle_heart)
/// };
///
/// assert_eq!("πŸ’–", sparkle_heart);
/// ```
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
String { vec: bytes }
}
/// Converts a `String` into a byte vector.
///
/// This consumes the `String`, so we do not need to copy its contents.
///
/// # Examples
///
/// ```
/// let s = String::from("hello");
/// let bytes = s.into_bytes();
///
/// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
/// ```
#[inline]
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
#[rustc_allow_const_fn_unstable(const_precise_live_drops)]
pub const fn into_bytes(self) -> Vec<u8> {
self.vec
}
/// Extracts a string slice containing the entire `String`.
///
/// # Examples
///
/// ```
/// let s = String::from("foo");
///
/// assert_eq!("foo", s.as_str());
/// ```
#[inline]
#[must_use]
#[stable(feature = "string_as_str", since = "1.7.0")]
#[rustc_diagnostic_item = "string_as_str"]
#[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
pub const fn as_str(&self) -> &str {
// SAFETY: String contents are stipulated to be valid UTF-8, invalid contents are an error
// at construction.
unsafe { str::from_utf8_unchecked(self.vec.as_slice()) }
}
/// Converts a `String` into a mutable string slice.
///
/// # Examples
///
/// ```
/// let mut s = String::from("foobar");
/// let s_mut_str = s.as_mut_str();
///
/// s_mut_str.make_ascii_uppercase();
///
/// assert_eq!("FOOBAR", s_mut_str);
/// ```
#[inline]
#[must_use]
#[stable(feature = "string_as_str", since = "1.7.0")]
#[rustc_diagnostic_item = "string_as_mut_str"]
#[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
pub const fn as_mut_str(&mut self) -> &mut str {
// SAFETY: String contents are stipulated to be valid UTF-8, invalid contents are an error
// at construction.
unsafe { str::from_utf8_unchecked_mut(self.vec.as_mut_slice()) }
}
/// Appends a given string slice onto the end of this `String`.
///
/// # Examples
///
/// ```
/// let mut s = String::from("foo");
///
/// s.push_str("bar");
///
/// assert_eq!("foobar", s);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_confusables("append", "push")]
#[rustc_diagnostic_item = "string_push_str"]
pub fn push_str(&mut self, string: &str) {
self.vec.extend_from_slice(string.as_bytes())
}
/// Copies elements from `src` range to the end of the string.
///
/// # Panics
///
/// Panics if the range has `start_bound > end_bound`, or, if the range is
/// bounded on either end and does not lie on a [`char`] boundary.
///
/// # Examples
///
/// ```
/// let mut string = String::from("abcde");
///
/// string.extend_from_within(2..);
/// assert_eq!(string, "abcdecde");
///
/// string.extend_from_within(..2);
/// assert_eq!(string, "abcdecdeab");
///
/// string.extend_from_within(4..8);
/// assert_eq!(string, "abcdecdeabecde");
/// ```
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "string_extend_from_within", since = "1.87.0")]
#[track_caller]
pub fn extend_from_within<R>(&mut self, src: R)
where
R: RangeBounds<usize>,
{
let src @ Range { start, end } = slice::range(src, ..self.len());
assert!(self.is_char_boundary(start));
assert!(self.is_char_boundary(end));
self.vec.extend_from_within(src);
}
/// Returns this `String`'s capacity, in bytes.
///
/// # Examples
///
/// ```
/// let s = String::with_capacity(10);
///
/// assert!(s.capacity() >= 10);
/// ```
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
pub const fn capacity(&self) -> usize {
self.vec.capacity()
}
/// Reserves capacity for at least `additional` bytes more than the
/// current length. The allocator may reserve more space to speculatively
/// avoid frequent allocations. After calling `reserve`,
/// capacity will be greater than or equal to `self.len() + additional`.
/// Does nothing if capacity is already sufficient.
///
/// # Panics
///
/// Panics if the new capacity overflows [`usize`].
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let mut s = String::new();
///
/// s.reserve(10);
///
/// assert!(s.capacity() >= 10);
/// ```
///
/// This might not actually increase the capacity:
///
/// ```
/// let mut s = String::with_capacity(10);
/// s.push('a');
/// s.push('b');
///
/// // s now has a length of 2 and a capacity of at least 10
/// let capacity = s.capacity();
/// assert_eq!(2, s.len());
/// assert!(capacity >= 10);
///
/// // Since we already have at least an extra 8 capacity, calling this...
/// s.reserve(8);
///
/// // ... doesn't actually increase.
/// assert_eq!(capacity, s.capacity());
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn reserve(&mut self, additional: usize) {
self.vec.reserve(additional)
}
/// Reserves the minimum capacity for at least `additional` bytes more than
/// the current length. Unlike [`reserve`], this will not
/// deliberately over-allocate to speculatively avoid frequent allocations.
/// After calling `reserve_exact`, capacity will be greater than or equal to
/// `self.len() + additional`. Does nothing if the capacity is already
/// sufficient.
///
/// [`reserve`]: String::reserve
///
/// # Panics
///
/// Panics if the new capacity overflows [`usize`].
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let mut s = String::new();
///
/// s.reserve_exact(10);
///
/// assert!(s.capacity() >= 10);
/// ```
///
/// This might not actually increase the capacity:
///
/// ```
/// let mut s = String::with_capacity(10);
/// s.push('a');
/// s.push('b');
///
/// // s now has a length of 2 and a capacity of at least 10
/// let capacity = s.capacity();
/// assert_eq!(2, s.len());
/// assert!(capacity >= 10);
///
/// // Since we already have at least an extra 8 capacity, calling this...
/// s.reserve_exact(8);
///
/// // ... doesn't actually increase.
/// assert_eq!(capacity, s.capacity());
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn reserve_exact(&mut self, additional: usize) {
self.vec.reserve_exact(additional)
}
/// Tries to reserve capacity for at least `additional` bytes more than the
/// current length. The allocator may reserve more space to speculatively
/// avoid frequent allocations. After calling `try_reserve`, capacity will be
/// greater than or equal to `self.len() + additional` if it returns
/// `Ok(())`. Does nothing if capacity is already sufficient. This method
/// preserves the contents even if an error occurs.
///
/// # Errors
///
/// If the capacity overflows, or the allocator reports a failure, then an error
/// is returned.
///
/// # Examples
///
/// ```
/// use std::collections::TryReserveError;
///
/// fn process_data(data: &str) -> Result<String, TryReserveError> {
/// let mut output = String::new();
///
/// // Pre-reserve the memory, exiting if we can't
/// output.try_reserve(data.len())?;
///
/// // Now we know this can't OOM in the middle of our complex work
/// output.push_str(data);
///
/// Ok(output)
/// }
/// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
/// ```
#[stable(feature = "try_reserve", since = "1.57.0")]
pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
self.vec.try_reserve(additional)
}
/// Tries to reserve the minimum capacity for at least `additional` bytes
/// more than the current length. Unlike [`try_reserve`], this will not
/// deliberately over-allocate to speculatively avoid frequent allocations.
/// After calling `try_reserve_exact`, capacity will be greater than or
/// equal to `self.len() + additional` if it returns `Ok(())`.
/// Does nothing if the capacity is already sufficient.
///
/// Note that the allocator may give the collection more space than it
/// requests. Therefore, capacity can not be relied upon to be precisely
/// minimal. Prefer [`try_reserve`] if future insertions are expected.
///
/// [`try_reserve`]: String::try_reserve
///
/// # Errors
///
/// If the capacity overflows, or the allocator reports a failure, then an error
/// is returned.
///
/// # Examples
///
/// ```
/// use std::collections::TryReserveError;
///
/// fn process_data(data: &str) -> Result<String, TryReserveError> {
/// let mut output = String::new();
///
/// // Pre-reserve the memory, exiting if we can't
/// output.try_reserve_exact(data.len())?;
///
/// // Now we know this can't OOM in the middle of our complex work
/// output.push_str(data);
///
/// Ok(output)
/// }
/// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
/// ```
#[stable(feature = "try_reserve", since = "1.57.0")]
pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
self.vec.try_reserve_exact(additional)
}
/// Shrinks the capacity of this `String` to match its length.
///
/// # Examples
///
/// ```
/// let mut s = String::from("foo");
///
/// s.reserve(100);
/// assert!(s.capacity() >= 100);
///
/// s.shrink_to_fit();
/// assert_eq!(3, s.capacity());
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn shrink_to_fit(&mut self) {
self.vec.shrink_to_fit()
}
/// Shrinks the capacity of this `String` with a lower bound.
///
/// The capacity will remain at least as large as both the length
/// and the supplied value.
///
/// If the current capacity is less than the lower limit, this is a no-op.
///
/// # Examples
///
/// ```
/// let mut s = String::from("foo");
///
/// s.reserve(100);
/// assert!(s.capacity() >= 100);
///
/// s.shrink_to(10);
/// assert!(s.capacity() >= 10);
/// s.shrink_to(0);
/// assert!(s.capacity() >= 3);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline]
#[stable(feature = "shrink_to", since = "1.56.0")]
pub fn shrink_to(&mut self, min_capacity: usize) {
self.vec.shrink_to(min_capacity)
}
/// Appends the given [`char`] to the end of this `String`.
///
/// # Examples
///
/// ```
/// let mut s = String::from("abc");
///
/// s.push('1');
/// s.push('2');
/// s.push('3');
///
/// assert_eq!("abc123", s);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn push(&mut self, ch: char) {
let len = self.len();
let ch_len = ch.len_utf8();
self.reserve(ch_len);
// SAFETY: Just reserved capacity for at least the length needed to encode `ch`.
unsafe {
core::char::encode_utf8_raw_unchecked(ch as u32, self.vec.as_mut_ptr().add(self.len()));
self.vec.set_len(len + ch_len);
}
}
/// Returns a byte slice of this `String`'s contents.
///
/// The inverse of this method is [`from_utf8`].
///
/// [`from_utf8`]: String::from_utf8
///
/// # Examples
///
/// ```
/// let s = String::from("hello");
///
/// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
/// ```
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
pub const fn as_bytes(&self) -> &[u8] {
self.vec.as_slice()
}
/// Shortens this `String` to the specified length.
///
/// If `new_len` is greater than or equal to the string's current length, this has no
/// effect.
///
/// Note that this method has no effect on the allocated capacity
/// of the string
///
/// # Panics
///
/// Panics if `new_len` does not lie on a [`char`] boundary.
///
/// # Examples
///
/// ```
/// let mut s = String::from("hello");
///
/// s.truncate(2);
///
/// assert_eq!("he", s);
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[track_caller]
pub fn truncate(&mut self, new_len: usize) {
if new_len <= self.len() {
assert!(self.is_char_boundary(new_len));
self.vec.truncate(new_len)
}
}
/// Removes the last character from the string buffer and returns it.
///
/// Returns [`None`] if this `String` is empty.
///
/// # Examples
///
/// ```
/// let mut s = String::from("abč");
///
/// assert_eq!(s.pop(), Some('č'));
/// assert_eq!(s.pop(), Some('b'));
/// assert_eq!(s.pop(), Some('a'));
///
/// assert_eq!(s.pop(), None);
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn pop(&mut self) -> Option<char> {
let ch = self.chars().rev().next()?;
let newlen = self.len() - ch.len_utf8();
unsafe {
self.vec.set_len(newlen);
}
Some(ch)
}
/// Removes a [`char`] from this `String` at byte position `idx` and returns it.
///
/// Copies all bytes after the removed char to new positions.
///
/// Note that calling this in a loop can result in quadratic behavior.
///
/// # Panics
///
/// Panics if `idx` is larger than or equal to the `String`'s length,
/// or if it does not lie on a [`char`] boundary.
///
/// # Examples
///
/// ```
/// let mut s = String::from("abç");
///
/// assert_eq!(s.remove(0), 'a');
/// assert_eq!(s.remove(1), 'Γ§');
/// assert_eq!(s.remove(0), 'b');
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[track_caller]
#[rustc_confusables("delete", "take")]
pub fn remove(&mut self, idx: usize) -> char {
let ch = match self[idx..].chars().next() {
Some(ch) => ch,
None => panic!("cannot remove a char from the end of a string"),
};
let next = idx + ch.len_utf8();
let len = self.len();
unsafe {
ptr::copy(self.vec.as_ptr().add(next), self.vec.as_mut_ptr().add(idx), len - next);
self.vec.set_len(len - (next - idx));
}
ch
}
/// Remove all matches of pattern `pat` in the `String`.
///
/// # Examples
///
/// ```
/// #![feature(string_remove_matches)]
/// let mut s = String::from("Trees are not green, the sky is not blue.");
/// s.remove_matches("not ");
/// assert_eq!("Trees are green, the sky is blue.", s);
/// ```
///
/// Matches will be detected and removed iteratively, so in cases where
/// patterns overlap, only the first pattern will be removed:
///
/// ```
/// #![feature(string_remove_matches)]
/// let mut s = String::from("banana");
/// s.remove_matches("ana");
/// assert_eq!("bna", s);
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "string_remove_matches", reason = "new API", issue = "72826")]
pub fn remove_matches<P: Pattern>(&mut self, pat: P) {
use core::str::pattern::Searcher;
let rejections = {
let mut searcher = pat.into_searcher(self);
// Per Searcher::next:
//
// A Match result needs to contain the whole matched pattern,
// however Reject results may be split up into arbitrary many
// adjacent fragments. Both ranges may have zero length.
//
// In practice the implementation of Searcher::next_match tends to
// be more efficient, so we use it here and do some work to invert
// matches into rejections since that's what we want to copy below.
let mut front = 0;
let rejections: Vec<_> = from_fn(|| {
let (start, end) = searcher.next_match()?;
let prev_front = front;
front = end;
Some((prev_front, start))
})
.collect();
rejections.into_iter().chain(core::iter::once((front, self.len())))
};
let mut len = 0;
let ptr = self.vec.as_mut_ptr();
for (start, end) in rejections {
let count = end - start;
if start != len {
// SAFETY: per Searcher::next:
//
// The stream of Match and Reject values up to a Done will
// contain index ranges that are adjacent, non-overlapping,
// covering the whole haystack, and laying on utf8
// boundaries.
unsafe {
ptr::copy(ptr.add(start), ptr.add(len), count);
}
}
len += count;
}
unsafe {
self.vec.set_len(len);
}
}
/// Retains only the characters specified by the predicate.
///
/// In other words, remove all characters `c` such that `f(c)` returns `false`.
/// This method operates in place, visiting each character exactly once in the
/// original order, and preserves the order of the retained characters.
///
/// # Examples
///
/// ```
/// let mut s = String::from("f_o_ob_ar");
///
/// s.retain(|c| c != '_');
///
/// assert_eq!(s, "foobar");
/// ```
///
/// Because the elements are visited exactly once in the original order,
/// external state may be used to decide which elements to keep.
///
/// ```
/// let mut s = String::from("abcde");
/// let keep = [false, true, true, false, true];
/// let mut iter = keep.iter();
/// s.retain(|_| *iter.next().unwrap());
/// assert_eq!(s, "bce");
/// ```
#[inline]
#[stable(feature = "string_retain", since = "1.26.0")]
pub fn retain<F>(&mut self, mut f: F)
where
F: FnMut(char) -> bool,
{
struct SetLenOnDrop<'a> {
s: &'a mut String,
idx: usize,
del_bytes: usize,
}
impl<'a> Drop for SetLenOnDrop<'a> {
fn drop(&mut self) {
let new_len = self.idx - self.del_bytes;
debug_assert!(new_len <= self.s.len());
unsafe { self.s.vec.set_len(new_len) };
}
}
let len = self.len();
let mut guard = SetLenOnDrop { s: self, idx: 0, del_bytes: 0 };
while guard.idx < len {
let ch =
// SAFETY: `guard.idx` is positive-or-zero and less that len so the `get_unchecked`
// is in bound. `self` is valid UTF-8 like string and the returned slice starts at
// a unicode code point so the `Chars` always return one character.
unsafe { guard.s.get_unchecked(guard.idx..len).chars().next().unwrap_unchecked() };
let ch_len = ch.len_utf8();
if !f(ch) {
guard.del_bytes += ch_len;
} else if guard.del_bytes > 0 {
// SAFETY: `guard.idx` is in bound and `guard.del_bytes` represent the number of
// bytes that are erased from the string so the resulting `guard.idx -
// guard.del_bytes` always represent a valid unicode code point.
//
// `guard.del_bytes` >= `ch.len_utf8()`, so taking a slice with `ch.len_utf8()` len
// is safe.
ch.encode_utf8(unsafe {
crate::slice::from_raw_parts_mut(
guard.s.as_mut_ptr().add(guard.idx - guard.del_bytes),
ch.len_utf8(),
)
});
}
// Point idx to the next char
guard.idx += ch_len;
}
drop(guard);
}
/// Inserts a character into this `String` at byte position `idx`.
///
/// Reallocates if `self.capacity()` is insufficient, which may involve copying all
/// `self.capacity()` bytes. Makes space for the insertion by copying all bytes of
/// `&self[idx..]` to new positions.
///
/// Note that calling this in a loop can result in quadratic behavior.
///
/// # Panics
///
/// Panics if `idx` is larger than the `String`'s length, or if it does not
/// lie on a [`char`] boundary.
///
/// # Examples
///
/// ```
/// let mut s = String::with_capacity(3);
///
/// s.insert(0, 'f');
/// s.insert(1, 'o');
/// s.insert(2, 'o');
///
/// assert_eq!("foo", s);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline]
#[track_caller]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_confusables("set")]
pub fn insert(&mut self, idx: usize, ch: char) {
assert!(self.is_char_boundary(idx));
let len = self.len();
let ch_len = ch.len_utf8();
self.reserve(ch_len);
// SAFETY: Move the bytes starting from `idx` to their new location `ch_len`
// bytes ahead. This is safe because sufficient capacity was reserved, and `idx`
// is a char boundary.
unsafe {
ptr::copy(
self.vec.as_ptr().add(idx),
self.vec.as_mut_ptr().add(idx + ch_len),
len - idx,
);
}
// SAFETY: Encode the character into the vacated region if `idx != len`,
// or into the uninitialized spare capacity otherwise.
unsafe {
core::char::encode_utf8_raw_unchecked(ch as u32, self.vec.as_mut_ptr().add(idx));
}
// SAFETY: Update the length to include the newly added bytes.
unsafe {
self.vec.set_len(len + ch_len);
}
}
/// Inserts a string slice into this `String` at byte position `idx`.
///
/// Reallocates if `self.capacity()` is insufficient, which may involve copying all
/// `self.capacity()` bytes. Makes space for the insertion by copying all bytes of
/// `&self[idx..]` to new positions.
///
/// Note that calling this in a loop can result in quadratic behavior.
///
/// # Panics
///
/// Panics if `idx` is larger than the `String`'s length, or if it does not
/// lie on a [`char`] boundary.
///
/// # Examples
///
/// ```
/// let mut s = String::from("bar");
///
/// s.insert_str(0, "foo");
///
/// assert_eq!("foobar", s);
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline]
#[track_caller]
#[stable(feature = "insert_str", since = "1.16.0")]
#[rustc_diagnostic_item = "string_insert_str"]
pub fn insert_str(&mut self, idx: usize, string: &str) {
assert!(self.is_char_boundary(idx));
let len = self.len();
let amt = string.len();
self.reserve(amt);
// SAFETY: Move the bytes starting from `idx` to their new location `amt` bytes
// ahead. This is safe because sufficient capacity was just reserved, and `idx`
// is a char boundary.
unsafe {
ptr::copy(self.vec.as_ptr().add(idx), self.vec.as_mut_ptr().add(idx + amt), len - idx);
}
// SAFETY: Copy the new string slice into the vacated region if `idx != len`,
// or into the uninitialized spare capacity otherwise. The borrow checker
// ensures that the source and destination do not overlap.
unsafe {
ptr::copy_nonoverlapping(string.as_ptr(), self.vec.as_mut_ptr().add(idx), amt);
}
// SAFETY: Update the length to include the newly added bytes.
unsafe {
self.vec.set_len(len + amt);
}
}
/// Returns a mutable reference to the contents of this `String`.
///
/// # Safety
///
/// This function is unsafe because the returned `&mut Vec` allows writing
/// bytes which are not valid UTF-8. If this constraint is violated, using
/// the original `String` after dropping the `&mut Vec` may violate memory
/// safety, as the rest of the standard library assumes that `String`s are
/// valid UTF-8.
///
/// # Examples
///
/// ```
/// let mut s = String::from("hello");
///
/// unsafe {
/// let vec = s.as_mut_vec();
/// assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
///
/// vec.reverse();
/// }
/// assert_eq!(s, "olleh");
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
pub const unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
&mut self.vec
}
/// Returns the length of this `String`, in bytes, not [`char`]s or
/// graphemes. In other words, it might not be what a human considers the
/// length of the string.
///
/// # Examples
///
/// ```
/// let a = String::from("foo");
/// assert_eq!(a.len(), 3);
///
/// let fancy_f = String::from("Ζ’oo");
/// assert_eq!(fancy_f.len(), 4);
/// assert_eq!(fancy_f.chars().count(), 3);
/// ```
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
#[rustc_confusables("length", "size")]
#[rustc_no_implicit_autorefs]
pub const fn len(&self) -> usize {
self.vec.len()
}
/// Returns `true` if this `String` has a length of zero, and `false` otherwise.
///
/// # Examples
///
/// ```
/// let mut v = String::new();
/// assert!(v.is_empty());
///
/// v.push('a');
/// assert!(!v.is_empty());
/// ```
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
#[rustc_no_implicit_autorefs]
pub const fn is_empty(&self) -> bool {
self.len() == 0
}
/// Splits the string into two at the given byte index.
///
/// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
/// the returned `String` contains bytes `[at, len)`. `at` must be on the
/// boundary of a UTF-8 code point.
///
/// Note that the capacity of `self` does not change.
///
/// # Panics
///
/// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
/// code point of the string.
///
/// # Examples
///
/// ```
/// # fn main() {
/// let mut hello = String::from("Hello, World!");
/// let world = hello.split_off(7);
/// assert_eq!(hello, "Hello, ");
/// assert_eq!(world, "World!");
/// # }
/// ```
#[cfg(not(no_global_oom_handling))]
#[inline]
#[track_caller]
#[stable(feature = "string_split_off", since = "1.16.0")]
#[must_use = "use `.truncate()` if you don't need the other half"]
pub fn split_off(&mut self, at: usize) -> String {
assert!(self.is_char_boundary(at));
let other = self.vec.split_off(at);
unsafe { String::from_utf8_unchecked(other) }
}
/// Truncates this `String`, removing all contents.
///
/// While this means the `String` will have a length of zero, it does not
/// touch its capacity.
///
/// # Examples
///
/// ```
/// let mut s = String::from("foo");
///
/// s.clear();
///
/// assert!(s.is_empty());
/// assert_eq!(0, s.len());
/// assert_eq!(3, s.capacity());
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn clear(&mut self) {
self.vec.clear()
}
/// Removes the specified range from the string in bulk, returning all
/// removed characters as an iterator.
///
/// The returned iterator keeps a mutable borrow on the string to optimize
/// its implementation.
///
/// # Panics
///
/// Panics if the range has `start_bound > end_bound`, or, if the range is
/// bounded on either end and does not lie on a [`char`] boundary.
///
/// # Leaking
///
/// If the returned iterator goes out of scope without being dropped (due to
/// [`core::mem::forget`], for example), the string may still contain a copy
/// of any drained characters, or may have lost characters arbitrarily,
/// including characters outside the range.
///
/// # Examples
///
/// ```
/// let mut s = String::from("Ξ± is alpha, Ξ² is beta");
/// let beta_offset = s.find('Ξ²').unwrap_or(s.len());
///
/// // Remove the range up until the Ξ² from the string
/// let t: String = s.drain(..beta_offset).collect();
/// assert_eq!(t, "Ξ± is alpha, ");
/// assert_eq!(s, "Ξ² is beta");
///
/// // A full range clears the string, like `clear()` does
/// s.drain(..);
/// assert_eq!(s, "");
/// ```
#[stable(feature = "drain", since = "1.6.0")]
#[track_caller]
pub fn drain<R>(&mut self, range: R) -> Drain<'_>
where
R: RangeBounds<usize>,
{
// Memory safety
//
// The String version of Drain does not have the memory safety issues
// of the vector version. The data is just plain bytes.
// Because the range removal happens in Drop, if the Drain iterator is leaked,
// the removal will not happen.
let Range { start, end } = slice::range(range, ..self.len());
assert!(self.is_char_boundary(start));
assert!(self.is_char_boundary(end));
// Take out two simultaneous borrows. The &mut String won't be accessed
// until iteration is over, in Drop.
let self_ptr = self as *mut _;
// SAFETY: `slice::range` and `is_char_boundary` do the appropriate bounds checks.
let chars_iter = unsafe { self.get_unchecked(start..end) }.chars();
Drain { start, end, iter: chars_iter, string: self_ptr }
}
/// Converts a `String` into an iterator over the [`char`]s of the string.
///
/// As a string consists of valid UTF-8, we can iterate through a string
/// by [`char`]. This method returns such an iterator.
///
/// It's important to remember that [`char`] represents a Unicode Scalar
/// Value, and might not match your idea of what a 'character' is. Iteration
/// over grapheme clusters may be what you actually want. That functionality
/// is not provided by Rust's standard library, check crates.io instead.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(string_into_chars)]
///
/// let word = String::from("goodbye");
///
/// let mut chars = word.into_chars();
///
/// assert_eq!(Some('g'), chars.next());
/// assert_eq!(Some('o'), chars.next());
/// assert_eq!(Some('o'), chars.next());
/// assert_eq!(Some('d'), chars.next());
/// assert_eq!(Some('b'), chars.next());
/// assert_eq!(Some('y'), chars.next());
/// assert_eq!(Some('e'), chars.next());
///
/// assert_eq!(None, chars.next());
/// ```
///
/// Remember, [`char`]s might not match your intuition about characters:
///
/// ```
/// #![feature(string_into_chars)]
///
/// let y = String::from("y̆");
///
/// let mut chars = y.into_chars();
///
/// assert_eq!(Some('y'), chars.next()); // not 'y̆'
/// assert_eq!(Some('\u{0306}'), chars.next());
///
/// assert_eq!(None, chars.next());
/// ```
///
/// [`char`]: prim@char
#[inline]
#[must_use = "`self` will be dropped if the result is not used"]
#[unstable(feature = "string_into_chars", issue = "133125")]
pub fn into_chars(self) -> IntoChars {
IntoChars { bytes: self.into_bytes().into_iter() }
}
/// Removes the specified range in the string,
/// and replaces it with the given string.
/// The given string doesn't need to be the same length as the range.
///
/// # Panics
///
/// Panics if the range has `start_bound > end_bound`, or, if the range is
/// bounded on either end and does not lie on a [`char`] boundary.
///
/// # Examples
///
/// ```
/// let mut s = String::from("Ξ± is alpha, Ξ² is beta");
/// let beta_offset = s.find('Ξ²').unwrap_or(s.len());
///
/// // Replace the range up until the Ξ² from the string
/// s.replace_range(..beta_offset, "Ξ‘ is capital alpha; ");
/// assert_eq!(s, "Ξ‘ is capital alpha; Ξ² is beta");
/// ```
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "splice", since = "1.27.0")]
#[track_caller]
pub fn replace_range<R>(&mut self, range: R, replace_with: &str)
where
R: RangeBounds<usize>,
{
// Memory safety
//
// Replace_range does not have the memory safety issues of a vector Splice.
// of the vector version. The data is just plain bytes.
// WARNING: Inlining this variable would be unsound (#81138)
let start = range.start_bound();
match start {
Included(&n) => assert!(self.is_char_boundary(n)),
Excluded(&n) => assert!(self.is_char_boundary(n + 1)),
Unbounded => {}
};
// WARNING: Inlining this variable would be unsound (#81138)
let end = range.end_bound();
match end {
Included(&n) => assert!(self.is_char_boundary(n + 1)),
Excluded(&n) => assert!(self.is_char_boundary(n)),
Unbounded => {}
};
// Using `range` again would be unsound (#81138)
// We assume the bounds reported by `range` remain the same, but
// an adversarial implementation could change between calls
unsafe { self.as_mut_vec() }.splice((start, end), replace_with.bytes());
}
/// Replaces the leftmost occurrence of a pattern with another string, in-place.
///
/// This method can be preferred over [`string = string.replacen(..., 1);`][replacen],
/// as it can use the `String`'s existing capacity to prevent a reallocation if
/// sufficient space is available.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(string_replace_in_place)]
///
/// let mut s = String::from("Test Results: ❌❌❌");
///
/// // Replace the leftmost ❌ with a βœ…
/// s.replace_first('❌', "βœ…");
/// assert_eq!(s, "Test Results: βœ…βŒβŒ");
/// ```
///
/// [replacen]: ../../std/primitive.str.html#method.replacen
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "string_replace_in_place", issue = "147949")]
pub fn replace_first<P: Pattern>(&mut self, from: P, to: &str) {
let range = match self.match_indices(from).next() {
Some((start, match_str)) => start..start + match_str.len(),
None => return,
};
self.replace_range(range, to);
}
/// Replaces the rightmost occurrence of a pattern with another string, in-place.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(string_replace_in_place)]
///
/// let mut s = String::from("Test Results: ❌❌❌");
///
/// // Replace the rightmost ❌ with a βœ…
/// s.replace_last('❌', "βœ…");
/// assert_eq!(s, "Test Results: βŒβŒβœ…");
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "string_replace_in_place", issue = "147949")]
pub fn replace_last<P: Pattern>(&mut self, from: P, to: &str)
where
for<'a> P::Searcher<'a>: core::str::pattern::ReverseSearcher<'a>,
{
let range = match self.rmatch_indices(from).next() {
Some((start, match_str)) => start..start + match_str.len(),
None => return,
};
self.replace_range(range, to);
}
/// Converts this `String` into a <code>[Box]<[str]></code>.
///
/// Before doing the conversion, this method discards excess capacity like [`shrink_to_fit`].
/// Note that this call may reallocate and copy the bytes of the string.
///
/// [`shrink_to_fit`]: String::shrink_to_fit
/// [str]: prim@str "str"
///
/// # Examples
///
/// ```
/// let s = String::from("hello");
///
/// let b = s.into_boxed_str();
/// ```
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "box_str", since = "1.4.0")]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline]
pub fn into_boxed_str(self) -> Box<str> {
let slice = self.vec.into_boxed_slice();
unsafe { from_boxed_utf8_unchecked(slice) }
}
/// Consumes and leaks the `String`, returning a mutable reference to the contents,
/// `&'a mut str`.
///
/// The caller has free choice over the returned lifetime, including `'static`. Indeed,
/// this function is ideally used for data that lives for the remainder of the program's life,
/// as dropping the returned reference will cause a memory leak.
///
/// It does not reallocate or shrink the `String`, so the leaked allocation may include unused
/// capacity that is not part of the returned slice. If you want to discard excess capacity,
/// call [`into_boxed_str`], and then [`Box::leak`] instead. However, keep in mind that
/// trimming the capacity may result in a reallocation and copy.
///
/// [`into_boxed_str`]: Self::into_boxed_str
///
/// # Examples
///
/// ```
/// let x = String::from("bucket");
/// let static_ref: &'static mut str = x.leak();
/// assert_eq!(static_ref, "bucket");
/// # // FIXME(https://github.com/rust-lang/miri/issues/3670):
/// # // use -Zmiri-disable-leak-check instead of unleaking in tests meant to leak.
/// # drop(unsafe { Box::from_raw(static_ref) });
/// ```
#[stable(feature = "string_leak", since = "1.72.0")]
#[inline]
pub fn leak<'a>(self) -> &'a mut str {
let slice = self.vec.leak();
unsafe { from_utf8_unchecked_mut(slice) }
}
}
impl FromUtf8Error {
/// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
///
/// # Examples
///
/// ```
/// // some invalid bytes, in a vector
/// let bytes = vec![0, 159];
///
/// let value = String::from_utf8(bytes);
///
/// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
/// ```
#[must_use]
#[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")]
pub fn as_bytes(&self) -> &[u8] {
&self.bytes[..]
}
/// Converts the bytes into a `String` lossily, substituting invalid UTF-8
/// sequences with replacement characters.
///
/// See [`String::from_utf8_lossy`] for more details on replacement of
/// invalid sequences, and [`String::from_utf8_lossy_owned`] for the
/// `String` function which corresponds to this function.
///
/// # Examples
///
/// ```
/// #![feature(string_from_utf8_lossy_owned)]
/// // some invalid bytes
/// let input: Vec<u8> = b"Hello \xF0\x90\x80World".into();
/// let output = String::from_utf8(input).unwrap_or_else(|e| e.into_utf8_lossy());
///
/// assert_eq!(String::from("Hello οΏ½World"), output);
/// ```
#[must_use]
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "string_from_utf8_lossy_owned", issue = "129436")]
pub fn into_utf8_lossy(self) -> String {
const REPLACEMENT: &str = "\u{FFFD}";
let mut res = {
let mut v = Vec::with_capacity(self.bytes.len());
// `Utf8Error::valid_up_to` returns the maximum index of validated
// UTF-8 bytes. Copy the valid bytes into the output buffer.
v.extend_from_slice(&self.bytes[..self.error.valid_up_to()]);
// SAFETY: This is safe because the only bytes present in the buffer
// were validated as UTF-8 by the call to `String::from_utf8` which
// produced this `FromUtf8Error`.
unsafe { String::from_utf8_unchecked(v) }
};
let iter = self.bytes[self.error.valid_up_to()..].utf8_chunks();
for chunk in iter {
res.push_str(chunk.valid());
if !chunk.invalid().is_empty() {
res.push_str(REPLACEMENT);
}
}
res
}
/// Returns the bytes that were attempted to convert to a `String`.
///
/// This method is carefully constructed to avoid allocation. It will
/// consume the error, moving out the bytes, so that a copy of the bytes
/// does not need to be made.
///
/// # Examples
///
/// ```
/// // some invalid bytes, in a vector
/// let bytes = vec![0, 159];
///
/// let value = String::from_utf8(bytes);
///
/// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn into_bytes(self) -> Vec<u8> {
self.bytes
}
/// Fetch a `Utf8Error` to get more details about the conversion failure.
///
/// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
/// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
/// an analogue to `FromUtf8Error`. See its documentation for more details
/// on using it.
///
/// [`std::str`]: core::str "std::str"
/// [`&str`]: prim@str "&str"
///
/// # Examples
///
/// ```
/// // some invalid bytes, in a vector
/// let bytes = vec![0, 159];
///
/// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
///
/// // the first byte is invalid here
/// assert_eq!(1, error.valid_up_to());
/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn utf8_error(&self) -> Utf8Error {
self.error
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for FromUtf8Error {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(&self.error, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for FromUtf16Error {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Error for FromUtf8Error {}
#[stable(feature = "rust1", since = "1.0.0")]
impl Error for FromUtf16Error {}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl Clone for String {
fn clone(&self) -> Self {
String { vec: self.vec.clone() }
}
/// Clones the contents of `source` into `self`.
///
/// This method is preferred over simply assigning `source.clone()` to `self`,
/// as it avoids reallocation if possible.
fn clone_from(&mut self, source: &Self) {
self.vec.clone_from(&source.vec);
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl FromIterator<char> for String {
fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
let mut buf = String::new();
buf.extend(iter);
buf
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
impl<'a> FromIterator<&'a char> for String {
fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
let mut buf = String::new();
buf.extend(iter);
buf
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a> FromIterator<&'a str> for String {
fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
let mut buf = String::new();
buf.extend(iter);
buf
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "extend_string", since = "1.4.0")]
impl FromIterator<String> for String {
fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
let mut iterator = iter.into_iter();
// Because we're iterating over `String`s, we can avoid at least
// one allocation by getting the first string from the iterator
// and appending to it all the subsequent strings.
match iterator.next() {
None => String::new(),
Some(mut buf) => {
buf.extend(iterator);
buf
}
}
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "box_str2", since = "1.45.0")]
impl<A: Allocator> FromIterator<Box<str, A>> for String {
fn from_iter<I: IntoIterator<Item = Box<str, A>>>(iter: I) -> String {
let mut buf = String::new();
buf.extend(iter);
buf
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "herd_cows", since = "1.19.0")]
impl<'a> FromIterator<Cow<'a, str>> for String {
fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
let mut iterator = iter.into_iter();
// Because we're iterating over CoWs, we can (potentially) avoid at least
// one allocation by getting the first item and appending to it all the
// subsequent items.
match iterator.next() {
None => String::new(),
Some(cow) => {
let mut buf = cow.into_owned();
buf.extend(iterator);
buf
}
}
}
}
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "ascii_char", issue = "110998")]
impl FromIterator<core::ascii::Char> for String {
fn from_iter<T: IntoIterator<Item = core::ascii::Char>>(iter: T) -> Self {
let buf = iter.into_iter().map(core::ascii::Char::to_u8).collect();
// SAFETY: `buf` is guaranteed to be valid UTF-8 because the `core::ascii::Char` type
// only contains ASCII values (0x00-0x7F), which are valid UTF-8.
unsafe { String::from_utf8_unchecked(buf) }
}
}
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "ascii_char", issue = "110998")]
impl<'a> FromIterator<&'a core::ascii::Char> for String {
fn from_iter<T: IntoIterator<Item = &'a core::ascii::Char>>(iter: T) -> Self {
let buf = iter.into_iter().copied().map(core::ascii::Char::to_u8).collect();
// SAFETY: `buf` is guaranteed to be valid UTF-8 because the `core::ascii::Char` type
// only contains ASCII values (0x00-0x7F), which are valid UTF-8.
unsafe { String::from_utf8_unchecked(buf) }
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl Extend<char> for String {
fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
let iterator = iter.into_iter();
let (lower_bound, _) = iterator.size_hint();
self.reserve(lower_bound);
iterator.for_each(move |c| self.push(c));
}
#[inline]
fn extend_one(&mut self, c: char) {
self.push(c);
}
#[inline]
fn extend_reserve(&mut self, additional: usize) {
self.reserve(additional);
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "extend_ref", since = "1.2.0")]
impl<'a> Extend<&'a char> for String {
fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
self.extend(iter.into_iter().cloned());
}
#[inline]
fn extend_one(&mut self, &c: &'a char) {
self.push(c);
}
#[inline]
fn extend_reserve(&mut self, additional: usize) {
self.reserve(additional);
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a> Extend<&'a str> for String {
fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
iter.into_iter().for_each(move |s| self.push_str(s));
}
#[inline]
fn extend_one(&mut self, s: &'a str) {
self.push_str(s);
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "box_str2", since = "1.45.0")]
impl<A: Allocator> Extend<Box<str, A>> for String {
fn extend<I: IntoIterator<Item = Box<str, A>>>(&mut self, iter: I) {
iter.into_iter().for_each(move |s| self.push_str(&s));
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "extend_string", since = "1.4.0")]
impl Extend<String> for String {
fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
iter.into_iter().for_each(move |s| self.push_str(&s));
}
#[inline]
fn extend_one(&mut self, s: String) {
self.push_str(&s);
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "herd_cows", since = "1.19.0")]
impl<'a> Extend<Cow<'a, str>> for String {
fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
iter.into_iter().for_each(move |s| self.push_str(&s));
}
#[inline]
fn extend_one(&mut self, s: Cow<'a, str>) {
self.push_str(&s);
}
}
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "ascii_char", issue = "110998")]
impl Extend<core::ascii::Char> for String {
#[inline]
fn extend<I: IntoIterator<Item = core::ascii::Char>>(&mut self, iter: I) {
self.vec.extend(iter.into_iter().map(|c| c.to_u8()));
}
#[inline]
fn extend_one(&mut self, c: core::ascii::Char) {
self.vec.push(c.to_u8());
}
}
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "ascii_char", issue = "110998")]
impl<'a> Extend<&'a core::ascii::Char> for String {
#[inline]
fn extend<I: IntoIterator<Item = &'a core::ascii::Char>>(&mut self, iter: I) {
self.extend(iter.into_iter().cloned());
}
#[inline]
fn extend_one(&mut self, c: &'a core::ascii::Char) {
self.vec.push(c.to_u8());
}
}
/// A convenience impl that delegates to the impl for `&str`.
///
/// # Examples
///
/// ```
/// assert_eq!(String::from("Hello world").find("world"), Some(6));
/// ```
#[unstable(
feature = "pattern",
reason = "API not fully fleshed out and ready to be stabilized",
issue = "27721"
)]
impl<'b> Pattern for &'b String {
type Searcher<'a> = <&'b str as Pattern>::Searcher<'a>;
fn into_searcher(self, haystack: &str) -> <&'b str as Pattern>::Searcher<'_> {
self[..].into_searcher(haystack)
}
#[inline]
fn is_contained_in(self, haystack: &str) -> bool {
self[..].is_contained_in(haystack)
}
#[inline]
fn is_prefix_of(self, haystack: &str) -> bool {
self[..].is_prefix_of(haystack)
}
#[inline]
fn strip_prefix_of(self, haystack: &str) -> Option<&str> {
self[..].strip_prefix_of(haystack)
}
#[inline]
fn is_suffix_of<'a>(self, haystack: &'a str) -> bool
where
Self::Searcher<'a>: core::str::pattern::ReverseSearcher<'a>,
{
self[..].is_suffix_of(haystack)
}
#[inline]
fn strip_suffix_of<'a>(self, haystack: &'a str) -> Option<&'a str>
where
Self::Searcher<'a>: core::str::pattern::ReverseSearcher<'a>,
{
self[..].strip_suffix_of(haystack)
}
#[inline]
fn as_utf8_pattern(&self) -> Option<Utf8Pattern<'_>> {
Some(Utf8Pattern::StringPattern(self.as_bytes()))
}
}
macro_rules! impl_eq {
($lhs:ty, $rhs: ty) => {
#[stable(feature = "rust1", since = "1.0.0")]
#[allow(unused_lifetimes)]
impl<'a, 'b> PartialEq<$rhs> for $lhs {
#[inline]
fn eq(&self, other: &$rhs) -> bool {
PartialEq::eq(&self[..], &other[..])
}
#[inline]
fn ne(&self, other: &$rhs) -> bool {
PartialEq::ne(&self[..], &other[..])
}
}
#[stable(feature = "rust1", since = "1.0.0")]
#[allow(unused_lifetimes)]
impl<'a, 'b> PartialEq<$lhs> for $rhs {
#[inline]
fn eq(&self, other: &$lhs) -> bool {
PartialEq::eq(&self[..], &other[..])
}
#[inline]
fn ne(&self, other: &$lhs) -> bool {
PartialEq::ne(&self[..], &other[..])
}
}
};
}
impl_eq! { String, str }
impl_eq! { String, &'a str }
#[cfg(not(no_global_oom_handling))]
impl_eq! { Cow<'a, str>, str }
#[cfg(not(no_global_oom_handling))]
impl_eq! { Cow<'a, str>, &'b str }
#[cfg(not(no_global_oom_handling))]
impl_eq! { Cow<'a, str>, String }
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_default", issue = "143894")]
impl const Default for String {
/// Creates an empty `String`.
#[inline]
fn default() -> String {
String::new()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for String {
#[inline]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(&**self, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Debug for String {
#[inline]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&**self, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl hash::Hash for String {
#[inline]
fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
(**self).hash(hasher)
}
}
/// Implements the `+` operator for concatenating two strings.
///
/// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
/// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
/// every operation, which would lead to *O*(*n*^2) running time when building an *n*-byte string by
/// repeated concatenation.
///
/// The string on the right-hand side is only borrowed; its contents are copied into the returned
/// `String`.
///
/// # Examples
///
/// Concatenating two `String`s takes the first by value and borrows the second:
///
/// ```
/// let a = String::from("hello");
/// let b = String::from(" world");
/// let c = a + &b;
/// // `a` is moved and can no longer be used here.
/// ```
///
/// If you want to keep using the first `String`, you can clone it and append to the clone instead:
///
/// ```
/// let a = String::from("hello");
/// let b = String::from(" world");
/// let c = a.clone() + &b;
/// // `a` is still valid here.
/// ```
///
/// Concatenating `&str` slices can be done by converting the first to a `String`:
///
/// ```
/// let a = "hello";
/// let b = " world";
/// let c = a.to_string() + b;
/// ```
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl Add<&str> for String {
type Output = String;
#[inline]
fn add(mut self, other: &str) -> String {
self.push_str(other);
self
}
}
/// Implements the `+=` operator for appending to a `String`.
///
/// This has the same behavior as the [`push_str`][String::push_str] method.
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "stringaddassign", since = "1.12.0")]
impl AddAssign<&str> for String {
#[inline]
fn add_assign(&mut self, other: &str) {
self.push_str(other);
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ops::Index<I> for String
where
I: slice::SliceIndex<str>,
{
type Output = I::Output;
#[inline]
fn index(&self, index: I) -> &I::Output {
index.index(self.as_str())
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ops::IndexMut<I> for String
where
I: slice::SliceIndex<str>,
{
#[inline]
fn index_mut(&mut self, index: I) -> &mut I::Output {
index.index_mut(self.as_mut_str())
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl ops::Deref for String {
type Target = str;
#[inline]
fn deref(&self) -> &str {
self.as_str()
}
}
#[unstable(feature = "deref_pure_trait", issue = "87121")]
unsafe impl ops::DerefPure for String {}
#[stable(feature = "derefmut_for_string", since = "1.3.0")]
impl ops::DerefMut for String {
#[inline]
fn deref_mut(&mut self) -> &mut str {
self.as_mut_str()
}
}
/// A type alias for [`Infallible`].
///
/// This alias exists for backwards compatibility, and may be eventually deprecated.
///
/// [`Infallible`]: core::convert::Infallible "convert::Infallible"
#[stable(feature = "str_parse_error", since = "1.5.0")]
pub type ParseError = core::convert::Infallible;
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl FromStr for String {
type Err = core::convert::Infallible;
#[inline]
fn from_str(s: &str) -> Result<String, Self::Err> {
Ok(String::from(s))
}
}
/// A trait for converting a value to a `String`.
///
/// This trait is automatically implemented for any type which implements the
/// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
/// [`Display`] should be implemented instead, and you get the `ToString`
/// implementation for free.
///
/// [`Display`]: fmt::Display
#[rustc_diagnostic_item = "ToString"]
#[stable(feature = "rust1", since = "1.0.0")]
pub trait ToString {
/// Converts the given value to a `String`.
///
/// # Examples
///
/// ```
/// let i = 5;
/// let five = String::from("5");
///
/// assert_eq!(five, i.to_string());
/// ```
#[rustc_conversion_suggestion]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_diagnostic_item = "to_string_method"]
fn to_string(&self) -> String;
}
/// # Panics
///
/// In this implementation, the `to_string` method panics
/// if the `Display` implementation returns an error.
/// This indicates an incorrect `Display` implementation
/// since `fmt::Write for String` never returns an error itself.
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: fmt::Display + ?Sized> ToString for T {
#[inline]
fn to_string(&self) -> String {
<Self as SpecToString>::spec_to_string(self)
}
}
#[cfg(not(no_global_oom_handling))]
trait SpecToString {
fn spec_to_string(&self) -> String;
}
#[cfg(not(no_global_oom_handling))]
impl<T: fmt::Display + ?Sized> SpecToString for T {
// A common guideline is to not inline generic functions. However,
// removing `#[inline]` from this method causes non-negligible regressions.
// See <https://github.com/rust-lang/rust/pull/74852>, the last attempt
// to try to remove it.
#[inline]
default fn spec_to_string(&self) -> String {
let mut buf = String::new();
let mut formatter =
core::fmt::Formatter::new(&mut buf, core::fmt::FormattingOptions::new());
// Bypass format_args!() to avoid write_str with zero-length strs
fmt::Display::fmt(self, &mut formatter)
.expect("a Display implementation returned an error unexpectedly");
buf
}
}
#[cfg(not(no_global_oom_handling))]
impl SpecToString for core::ascii::Char {
#[inline]
fn spec_to_string(&self) -> String {
self.as_str().to_owned()
}
}
#[cfg(not(no_global_oom_handling))]
impl SpecToString for char {
#[inline]
fn spec_to_string(&self) -> String {
String::from(self.encode_utf8(&mut [0; char::MAX_LEN_UTF8]))
}
}
#[cfg(not(no_global_oom_handling))]
impl SpecToString for bool {
#[inline]
fn spec_to_string(&self) -> String {
String::from(if *self { "true" } else { "false" })
}
}
macro_rules! impl_to_string {
($($signed:ident, $unsigned:ident,)*) => {
$(
#[cfg(not(no_global_oom_handling))]
#[cfg(not(feature = "optimize_for_size"))]
impl SpecToString for $signed {
#[inline]
fn spec_to_string(&self) -> String {
const SIZE: usize = $signed::MAX.ilog10() as usize + 1;
let mut buf = [core::mem::MaybeUninit::<u8>::uninit(); SIZE];
// Only difference between signed and unsigned are these 8 lines.
let mut out;
if *self < 0 {
out = String::with_capacity(SIZE + 1);
out.push('-');
} else {
out = String::with_capacity(SIZE);
}
// SAFETY: `buf` is always big enough to contain all the digits.
unsafe { out.push_str(self.unsigned_abs()._fmt(&mut buf)); }
out
}
}
#[cfg(not(no_global_oom_handling))]
#[cfg(not(feature = "optimize_for_size"))]
impl SpecToString for $unsigned {
#[inline]
fn spec_to_string(&self) -> String {
const SIZE: usize = $unsigned::MAX.ilog10() as usize + 1;
let mut buf = [core::mem::MaybeUninit::<u8>::uninit(); SIZE];
// SAFETY: `buf` is always big enough to contain all the digits.
unsafe { self._fmt(&mut buf).to_string() }
}
}
)*
}
}
impl_to_string! {
i8, u8,
i16, u16,
i32, u32,
i64, u64,
isize, usize,
i128, u128,
}
#[cfg(not(no_global_oom_handling))]
#[cfg(feature = "optimize_for_size")]
impl SpecToString for u8 {
#[inline]
fn spec_to_string(&self) -> String {
let mut buf = String::with_capacity(3);
let mut n = *self;
if n >= 10 {
if n >= 100 {
buf.push((b'0' + n / 100) as char);
n %= 100;
}
buf.push((b'0' + n / 10) as char);
n %= 10;
}
buf.push((b'0' + n) as char);
buf
}
}
#[cfg(not(no_global_oom_handling))]
#[cfg(feature = "optimize_for_size")]
impl SpecToString for i8 {
#[inline]
fn spec_to_string(&self) -> String {
let mut buf = String::with_capacity(4);
if self.is_negative() {
buf.push('-');
}
let mut n = self.unsigned_abs();
if n >= 10 {
if n >= 100 {
buf.push('1');
n -= 100;
}
buf.push((b'0' + n / 10) as char);
n %= 10;
}
buf.push((b'0' + n) as char);
buf
}
}
#[cfg(not(no_global_oom_handling))]
macro_rules! to_string_str {
{$($type:ty,)*} => {
$(
impl SpecToString for $type {
#[inline]
fn spec_to_string(&self) -> String {
let s: &str = self;
String::from(s)
}
}
)*
};
}
#[cfg(not(no_global_oom_handling))]
to_string_str! {
Cow<'_, str>,
String,
// Generic/generated code can sometimes have multiple, nested references
// for strings, including `&&&str`s that would never be written
// by hand.
&&&&&&&&&&&&str,
&&&&&&&&&&&str,
&&&&&&&&&&str,
&&&&&&&&&str,
&&&&&&&&str,
&&&&&&&str,
&&&&&&str,
&&&&&str,
&&&&str,
&&&str,
&&str,
&str,
str,
}
#[cfg(not(no_global_oom_handling))]
impl SpecToString for fmt::Arguments<'_> {
#[inline]
fn spec_to_string(&self) -> String {
crate::fmt::format(*self)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl AsRef<str> for String {
#[inline]
fn as_ref(&self) -> &str {
self
}
}
#[stable(feature = "string_as_mut", since = "1.43.0")]
impl AsMut<str> for String {
#[inline]
fn as_mut(&mut self) -> &mut str {
self
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl AsRef<[u8]> for String {
#[inline]
fn as_ref(&self) -> &[u8] {
self.as_bytes()
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl From<&str> for String {
/// Converts a `&str` into a [`String`].
///
/// The result is allocated on the heap.
#[inline]
fn from(s: &str) -> String {
s.to_owned()
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "from_mut_str_for_string", since = "1.44.0")]
impl From<&mut str> for String {
/// Converts a `&mut str` into a [`String`].
///
/// The result is allocated on the heap.
#[inline]
fn from(s: &mut str) -> String {
s.to_owned()
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "from_ref_string", since = "1.35.0")]
impl From<&String> for String {
/// Converts a `&String` into a [`String`].
///
/// This clones `s` and returns the clone.
#[inline]
fn from(s: &String) -> String {
s.clone()
}
}
// note: test pulls in std, which causes errors here
#[stable(feature = "string_from_box", since = "1.18.0")]
impl From<Box<str>> for String {
/// Converts the given boxed `str` slice to a [`String`].
/// It is notable that the `str` slice is owned.
///
/// # Examples
///
/// ```
/// let s1: String = String::from("hello world");
/// let s2: Box<str> = s1.into_boxed_str();
/// let s3: String = String::from(s2);
///
/// assert_eq!("hello world", s3)
/// ```
fn from(s: Box<str>) -> String {
s.into_string()
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "box_from_str", since = "1.20.0")]
impl From<String> for Box<str> {
/// Converts the given [`String`] to a boxed `str` slice that is owned.
///
/// # Examples
///
/// ```
/// let s1: String = String::from("hello world");
/// let s2: Box<str> = Box::from(s1);
/// let s3: String = String::from(s2);
///
/// assert_eq!("hello world", s3)
/// ```
fn from(s: String) -> Box<str> {
s.into_boxed_str()
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "string_from_cow_str", since = "1.14.0")]
impl<'a> From<Cow<'a, str>> for String {
/// Converts a clone-on-write string to an owned
/// instance of [`String`].
///
/// This extracts the owned string,
/// clones the string if it is not already owned.
///
/// # Example
///
/// ```
/// # use std::borrow::Cow;
/// // If the string is not owned...
/// let cow: Cow<'_, str> = Cow::Borrowed("eggplant");
/// // It will allocate on the heap and copy the string.
/// let owned: String = String::from(cow);
/// assert_eq!(&owned[..], "eggplant");
/// ```
fn from(s: Cow<'a, str>) -> String {
s.into_owned()
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a> From<&'a str> for Cow<'a, str> {
/// Converts a string slice into a [`Borrowed`] variant.
/// No heap allocation is performed, and the string
/// is not copied.
///
/// # Example
///
/// ```
/// # use std::borrow::Cow;
/// assert_eq!(Cow::from("eggplant"), Cow::Borrowed("eggplant"));
/// ```
///
/// [`Borrowed`]: crate::borrow::Cow::Borrowed "borrow::Cow::Borrowed"
#[inline]
fn from(s: &'a str) -> Cow<'a, str> {
Cow::Borrowed(s)
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a> From<String> for Cow<'a, str> {
/// Converts a [`String`] into an [`Owned`] variant.
/// No heap allocation is performed, and the string
/// is not copied.
///
/// # Example
///
/// ```
/// # use std::borrow::Cow;
/// let s = "eggplant".to_string();
/// let s2 = "eggplant".to_string();
/// assert_eq!(Cow::from(s), Cow::<'static, str>::Owned(s2));
/// ```
///
/// [`Owned`]: crate::borrow::Cow::Owned "borrow::Cow::Owned"
#[inline]
fn from(s: String) -> Cow<'a, str> {
Cow::Owned(s)
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "cow_from_string_ref", since = "1.28.0")]
impl<'a> From<&'a String> for Cow<'a, str> {
/// Converts a [`String`] reference into a [`Borrowed`] variant.
/// No heap allocation is performed, and the string
/// is not copied.
///
/// # Example
///
/// ```
/// # use std::borrow::Cow;
/// let s = "eggplant".to_string();
/// assert_eq!(Cow::from(&s), Cow::Borrowed("eggplant"));
/// ```
///
/// [`Borrowed`]: crate::borrow::Cow::Borrowed "borrow::Cow::Borrowed"
#[inline]
fn from(s: &'a String) -> Cow<'a, str> {
Cow::Borrowed(s.as_str())
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "cow_str_from_iter", since = "1.12.0")]
impl<'a> FromIterator<char> for Cow<'a, str> {
fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
Cow::Owned(FromIterator::from_iter(it))
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "cow_str_from_iter", since = "1.12.0")]
impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
Cow::Owned(FromIterator::from_iter(it))
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "cow_str_from_iter", since = "1.12.0")]
impl<'a> FromIterator<String> for Cow<'a, str> {
fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
Cow::Owned(FromIterator::from_iter(it))
}
}
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "ascii_char", issue = "110998")]
impl<'a> FromIterator<core::ascii::Char> for Cow<'a, str> {
fn from_iter<T: IntoIterator<Item = core::ascii::Char>>(it: T) -> Self {
Cow::Owned(FromIterator::from_iter(it))
}
}
#[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
impl From<String> for Vec<u8> {
/// Converts the given [`String`] to a vector [`Vec`] that holds values of type [`u8`].
///
/// # Examples
///
/// ```
/// let s1 = String::from("hello world");
/// let v1 = Vec::from(s1);
///
/// for b in v1 {
/// println!("{b}");
/// }
/// ```
fn from(string: String) -> Vec<u8> {
string.into_bytes()
}
}
#[stable(feature = "try_from_vec_u8_for_string", since = "1.87.0")]
impl TryFrom<Vec<u8>> for String {
type Error = FromUtf8Error;
/// Converts the given [`Vec<u8>`] into a [`String`] if it contains valid UTF-8 data.
///
/// # Examples
///
/// ```
/// let s1 = b"hello world".to_vec();
/// let v1 = String::try_from(s1).unwrap();
/// assert_eq!(v1, "hello world");
///
/// ```
fn try_from(bytes: Vec<u8>) -> Result<Self, Self::Error> {
Self::from_utf8(bytes)
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Write for String {
#[inline]
fn write_str(&mut self, s: &str) -> fmt::Result {
self.push_str(s);
Ok(())
}
#[inline]
fn write_char(&mut self, c: char) -> fmt::Result {
self.push(c);
Ok(())
}
}
/// An iterator over the [`char`]s of a string.
///
/// This struct is created by the [`into_chars`] method on [`String`].
/// See its documentation for more.
///
/// [`char`]: prim@char
/// [`into_chars`]: String::into_chars
#[cfg_attr(not(no_global_oom_handling), derive(Clone))]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[unstable(feature = "string_into_chars", issue = "133125")]
pub struct IntoChars {
bytes: vec::IntoIter<u8>,
}
#[unstable(feature = "string_into_chars", issue = "133125")]
impl fmt::Debug for IntoChars {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_tuple("IntoChars").field(&self.as_str()).finish()
}
}
impl IntoChars {
/// Views the underlying data as a subslice of the original data.
///
/// # Examples
///
/// ```
/// #![feature(string_into_chars)]
///
/// let mut chars = String::from("abc").into_chars();
///
/// assert_eq!(chars.as_str(), "abc");
/// chars.next();
/// assert_eq!(chars.as_str(), "bc");
/// chars.next();
/// chars.next();
/// assert_eq!(chars.as_str(), "");
/// ```
#[unstable(feature = "string_into_chars", issue = "133125")]
#[must_use]
#[inline]
pub fn as_str(&self) -> &str {
// SAFETY: `bytes` is a valid UTF-8 string.
unsafe { str::from_utf8_unchecked(self.bytes.as_slice()) }
}
/// Consumes the `IntoChars`, returning the remaining string.
///
/// # Examples
///
/// ```
/// #![feature(string_into_chars)]
///
/// let chars = String::from("abc").into_chars();
/// assert_eq!(chars.into_string(), "abc");
///
/// let mut chars = String::from("def").into_chars();
/// chars.next();
/// assert_eq!(chars.into_string(), "ef");
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "string_into_chars", issue = "133125")]
#[inline]
pub fn into_string(self) -> String {
// Safety: `bytes` are kept in UTF-8 form, only removing whole `char`s at a time.
unsafe { String::from_utf8_unchecked(self.bytes.collect()) }
}
#[inline]
fn iter(&self) -> CharIndices<'_> {
self.as_str().char_indices()
}
}
#[unstable(feature = "string_into_chars", issue = "133125")]
impl Iterator for IntoChars {
type Item = char;
#[inline]
fn next(&mut self) -> Option<char> {
let mut iter = self.iter();
match iter.next() {
None => None,
Some((_, ch)) => {
let offset = iter.offset();
// `offset` is a valid index.
let _ = self.bytes.advance_by(offset);
Some(ch)
}
}
}
#[inline]
fn count(self) -> usize {
self.iter().count()
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter().size_hint()
}
#[inline]
fn last(mut self) -> Option<char> {
self.next_back()
}
}
#[unstable(feature = "string_into_chars", issue = "133125")]
impl DoubleEndedIterator for IntoChars {
#[inline]
fn next_back(&mut self) -> Option<char> {
let len = self.as_str().len();
let mut iter = self.iter();
match iter.next_back() {
None => None,
Some((idx, ch)) => {
// `idx` is a valid index.
let _ = self.bytes.advance_back_by(len - idx);
Some(ch)
}
}
}
}
#[unstable(feature = "string_into_chars", issue = "133125")]
impl FusedIterator for IntoChars {}
/// A draining iterator for `String`.
///
/// This struct is created by the [`drain`] method on [`String`]. See its
/// documentation for more.
///
/// [`drain`]: String::drain
#[stable(feature = "drain", since = "1.6.0")]
pub struct Drain<'a> {
/// Will be used as &'a mut String in the destructor
string: *mut String,
/// Start of part to remove
start: usize,
/// End of part to remove
end: usize,
/// Current remaining range to remove
iter: Chars<'a>,
}
#[stable(feature = "collection_debug", since = "1.17.0")]
impl fmt::Debug for Drain<'_> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_tuple("Drain").field(&self.as_str()).finish()
}
}
#[stable(feature = "drain", since = "1.6.0")]
unsafe impl Sync for Drain<'_> {}
#[stable(feature = "drain", since = "1.6.0")]
unsafe impl Send for Drain<'_> {}
#[stable(feature = "drain", since = "1.6.0")]
impl Drop for Drain<'_> {
fn drop(&mut self) {
unsafe {
// Use Vec::drain. "Reaffirm" the bounds checks to avoid
// panic code being inserted again.
let self_vec = (*self.string).as_mut_vec();
if self.start <= self.end && self.end <= self_vec.len() {
self_vec.drain(self.start..self.end);
}
}
}
}
impl<'a> Drain<'a> {
/// Returns the remaining (sub)string of this iterator as a slice.
///
/// # Examples
///
/// ```
/// let mut s = String::from("abc");
/// let mut drain = s.drain(..);
/// assert_eq!(drain.as_str(), "abc");
/// let _ = drain.next().unwrap();
/// assert_eq!(drain.as_str(), "bc");
/// ```
#[must_use]
#[stable(feature = "string_drain_as_str", since = "1.55.0")]
pub fn as_str(&self) -> &str {
self.iter.as_str()
}
}
#[stable(feature = "string_drain_as_str", since = "1.55.0")]
impl<'a> AsRef<str> for Drain<'a> {
fn as_ref(&self) -> &str {
self.as_str()
}
}
#[stable(feature = "string_drain_as_str", since = "1.55.0")]
impl<'a> AsRef<[u8]> for Drain<'a> {
fn as_ref(&self) -> &[u8] {
self.as_str().as_bytes()
}
}
#[stable(feature = "drain", since = "1.6.0")]
impl Iterator for Drain<'_> {
type Item = char;
#[inline]
fn next(&mut self) -> Option<char> {
self.iter.next()
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
#[inline]
fn last(mut self) -> Option<char> {
self.next_back()
}
}
#[stable(feature = "drain", since = "1.6.0")]
impl DoubleEndedIterator for Drain<'_> {
#[inline]
fn next_back(&mut self) -> Option<char> {
self.iter.next_back()
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl FusedIterator for Drain<'_> {}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "from_char_for_string", since = "1.46.0")]
impl From<char> for String {
/// Allocates an owned [`String`] from a single character.
///
/// # Example
/// ```rust
/// let c: char = 'a';
/// let s: String = String::from(c);
/// assert_eq!("a", &s[..]);
/// ```
#[inline]
fn from(c: char) -> Self {
c.to_string()
}
}