library/core/src/iter/adapters/enumerate.rs - rust - Git at Google

 use crate::iter::adapters::zip::try_get_unchecked;
 use crate::iter::adapters::{SourceIter, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
 use crate::iter::{FusedIterator, InPlaceIterable, TrustedFused, TrustedLen};
 use crate::num::NonZero;
 use crate::ops::Try;

 /// An iterator that yields the current count and the element during iteration.
 ///
 /// This `struct` is created by the [`enumerate`] method on [`Iterator`]. See its
 /// documentation for more.
 ///
 /// [`enumerate`]: Iterator::enumerate
 /// [`Iterator`]: trait.Iterator.html
 #[derive(Clone, Debug)]
 #[must_use = "iterators are lazy and do nothing unless consumed"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_diagnostic_item = "Enumerate"]
 pub struct Enumerate<I> {
     iter: I,
     count: usize,
 }
 impl<I> Enumerate<I> {
     pub(in crate::iter) fn new(iter: I) -> Enumerate<I> {
         Enumerate { iter, count: 0 }
     }

     /// Retrieve the current position of the iterator.
     ///
     /// If the iterator has not advanced, the position returned will be 0.
     ///
     /// The position may also exceed the bounds of the iterator to allow for calculating
     /// the displacement of the iterator from following calls to [`Iterator::next`].
     ///
     /// # Examples
     ///
     /// ```
     /// #![feature(next_index)]
     ///
     /// let arr = ['a', 'b'];
     ///
     /// let mut iter = arr.iter().enumerate();
     ///
     /// assert_eq!(iter.next_index(), 0);
     /// assert_eq!(iter.next(), Some((0, &'a')));
     ///
     /// assert_eq!(iter.next_index(), 1);
     /// assert_eq!(iter.next_index(), 1);
     /// assert_eq!(iter.next(), Some((1, &'b')));
     ///
     /// assert_eq!(iter.next_index(), 2);
     /// assert_eq!(iter.next(), None);
     /// assert_eq!(iter.next_index(), 2);
     /// ```
     #[inline]
     #[unstable(feature = "next_index", issue = "130711")]
     pub fn next_index(&self) -> usize {
         self.count
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<I> Iterator for Enumerate<I>
 where
     I: Iterator,
 {
     type Item = (usize, <I as Iterator>::Item);

     /// # Overflow Behavior
     ///
     /// The method does no guarding against overflows, so enumerating more than
     /// `usize::MAX` elements either produces the wrong result or panics. If
     /// overflow checks are enabled, a panic is guaranteed.
     ///
     /// # Panics
     ///
     /// Might panic if the index of the element overflows a `usize`.
     #[inline]
     #[rustc_inherit_overflow_checks]
     fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
         let a = self.iter.next()?;
         let i = self.count;
         self.count += 1;
         Some((i, a))
     }

     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.iter.size_hint()
     }

     #[inline]
     #[rustc_inherit_overflow_checks]
     fn nth(&mut self, n: usize) -> Option<(usize, I::Item)> {
         let a = self.iter.nth(n)?;
         let i = self.count + n;
         self.count = i + 1;
         Some((i, a))
     }

     #[inline]
     fn count(self) -> usize {
         self.iter.count()
     }

     #[inline]
     fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
         R: Try<Output = Acc>,
     {
         #[inline]
         fn enumerate<'a, T, Acc, R>(
             count: &'a mut usize,
             mut fold: impl FnMut(Acc, (usize, T)) -> R + 'a,
         ) -> impl FnMut(Acc, T) -> R + 'a {
             #[rustc_inherit_overflow_checks]
             move |acc, item| {
                 let acc = fold(acc, (*count, item));
                 *count += 1;
                 acc
             }
         }

         self.iter.try_fold(init, enumerate(&mut self.count, fold))
     }

     #[inline]
     fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
     where
         Fold: FnMut(Acc, Self::Item) -> Acc,
     {
         #[inline]
         fn enumerate<T, Acc>(
             mut count: usize,
             mut fold: impl FnMut(Acc, (usize, T)) -> Acc,
         ) -> impl FnMut(Acc, T) -> Acc {
             #[rustc_inherit_overflow_checks]
             move |acc, item| {
                 let acc = fold(acc, (count, item));
                 count += 1;
                 acc
             }
         }

         self.iter.fold(init, enumerate(self.count, fold))
     }

     #[inline]
     #[rustc_inherit_overflow_checks]
     fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
         let remaining = self.iter.advance_by(n);
         let advanced = match remaining {
             Ok(()) => n,
             Err(rem) => n - rem.get(),
         };
         self.count += advanced;
         remaining
     }

     #[rustc_inherit_overflow_checks]
     #[inline]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> <Self as Iterator>::Item
     where
         Self: TrustedRandomAccessNoCoerce,
     {
         // SAFETY: the caller must uphold the contract for
         // `Iterator::__iterator_get_unchecked`.
         let value = unsafe { try_get_unchecked(&mut self.iter, idx) };
         (self.count + idx, value)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<I> DoubleEndedIterator for Enumerate<I>
 where
     I: ExactSizeIterator + DoubleEndedIterator,
 {
     #[inline]
     fn next_back(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
         let a = self.iter.next_back()?;
         let len = self.iter.len();
         // Can safely add, `ExactSizeIterator` promises that the number of
         // elements fits into a `usize`.
         Some((self.count + len, a))
     }

     #[inline]
     fn nth_back(&mut self, n: usize) -> Option<(usize, <I as Iterator>::Item)> {
         let a = self.iter.nth_back(n)?;
         let len = self.iter.len();
         // Can safely add, `ExactSizeIterator` promises that the number of
         // elements fits into a `usize`.
         Some((self.count + len, a))
     }

     #[inline]
     fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
         R: Try<Output = Acc>,
     {
         // Can safely add and subtract the count, as `ExactSizeIterator` promises
         // that the number of elements fits into a `usize`.
         fn enumerate<T, Acc, R>(
             mut count: usize,
             mut fold: impl FnMut(Acc, (usize, T)) -> R,
         ) -> impl FnMut(Acc, T) -> R {
             move |acc, item| {
                 count -= 1;
                 fold(acc, (count, item))
             }
         }

         let count = self.count + self.iter.len();
         self.iter.try_rfold(init, enumerate(count, fold))
     }

     #[inline]
     fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
     where
         Fold: FnMut(Acc, Self::Item) -> Acc,
     {
         // Can safely add and subtract the count, as `ExactSizeIterator` promises
         // that the number of elements fits into a `usize`.
         fn enumerate<T, Acc>(
             mut count: usize,
             mut fold: impl FnMut(Acc, (usize, T)) -> Acc,
         ) -> impl FnMut(Acc, T) -> Acc {
             move |acc, item| {
                 count -= 1;
                 fold(acc, (count, item))
             }
         }

         let count = self.count + self.iter.len();
         self.iter.rfold(init, enumerate(count, fold))
     }

     #[inline]
     fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
         // we do not need to update the count since that only tallies the number of items
         // consumed from the front. consuming items from the back can never reduce that.
         self.iter.advance_back_by(n)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<I> ExactSizeIterator for Enumerate<I>
 where
     I: ExactSizeIterator,
 {
     fn len(&self) -> usize {
         self.iter.len()
     }

     fn is_empty(&self) -> bool {
         self.iter.is_empty()
     }
 }

 #[doc(hidden)]
 #[unstable(feature = "trusted_random_access", issue = "none")]
 unsafe impl<I> TrustedRandomAccess for Enumerate<I> where I: TrustedRandomAccess {}

 #[doc(hidden)]
 #[unstable(feature = "trusted_random_access", issue = "none")]
 unsafe impl<I> TrustedRandomAccessNoCoerce for Enumerate<I>
 where
     I: TrustedRandomAccessNoCoerce,
 {
     const MAY_HAVE_SIDE_EFFECT: bool = I::MAY_HAVE_SIDE_EFFECT;
 }

 #[stable(feature = "fused", since = "1.26.0")]
 impl<I> FusedIterator for Enumerate<I> where I: FusedIterator {}

 #[unstable(issue = "none", feature = "trusted_fused")]
 unsafe impl<I: TrustedFused> TrustedFused for Enumerate<I> {}

 #[unstable(feature = "trusted_len", issue = "37572")]
 unsafe impl<I> TrustedLen for Enumerate<I> where I: TrustedLen {}

 #[unstable(issue = "none", feature = "inplace_iteration")]
 unsafe impl<I> SourceIter for Enumerate<I>
 where
     I: SourceIter,
 {
     type Source = I::Source;

     #[inline]
     unsafe fn as_inner(&mut self) -> &mut I::Source {
         // SAFETY: unsafe function forwarding to unsafe function with the same requirements
         unsafe { SourceIter::as_inner(&mut self.iter) }
     }
 }

 #[unstable(issue = "none", feature = "inplace_iteration")]
 unsafe impl<I: InPlaceIterable> InPlaceIterable for Enumerate<I> {
     const EXPAND_BY: Option<NonZero<usize>> = I::EXPAND_BY;
     const MERGE_BY: Option<NonZero<usize>> = I::MERGE_BY;
 }

 #[stable(feature = "default_iters", since = "1.70.0")]
 impl<I: Default> Default for Enumerate<I> {
     /// Creates an `Enumerate` iterator from the default value of `I`
     /// ```
     /// # use core::slice;
     /// # use std::iter::Enumerate;
     /// let iter: Enumerate<slice::Iter<'_, u8>> = Default::default();
     /// assert_eq!(iter.len(), 0);
     /// ```
     fn default() -> Self {
         Enumerate::new(Default::default())
     }
 }
	use crate::iter::adapters::zip::try_get_unchecked;
	use crate::iter::adapters::{SourceIter, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
	use crate::iter::{FusedIterator, InPlaceIterable, TrustedFused, TrustedLen};
	use crate::num::NonZero;
	use crate::ops::Try;

	/// An iterator that yields the current count and the element during iteration.
	///
	/// This `struct` is created by the [`enumerate`] method on [`Iterator`]. See its
	/// documentation for more.
	///
	/// [`enumerate`]: Iterator::enumerate
	/// [`Iterator`]: trait.Iterator.html
	#[derive(Clone, Debug)]
	#[must_use = "iterators are lazy and do nothing unless consumed"]
	#[stable(feature = "rust1", since = "1.0.0")]
	#[rustc_diagnostic_item = "Enumerate"]
	pub struct Enumerate<I> {
	iter: I,
	count: usize,
	}
	impl<I> Enumerate<I> {
	pub(in crate::iter) fn new(iter: I) -> Enumerate<I> {
	Enumerate { iter, count: 0 }
	}

	/// Retrieve the current position of the iterator.
	///
	/// If the iterator has not advanced, the position returned will be 0.
	///
	/// The position may also exceed the bounds of the iterator to allow for calculating
	/// the displacement of the iterator from following calls to [`Iterator::next`].
	///
	/// # Examples
	///
	/// ```
	/// #![feature(next_index)]
	///
	/// let arr = ['a', 'b'];
	///
	/// let mut iter = arr.iter().enumerate();
	///
	/// assert_eq!(iter.next_index(), 0);
	/// assert_eq!(iter.next(), Some((0, &'a')));
	///
	/// assert_eq!(iter.next_index(), 1);
	/// assert_eq!(iter.next_index(), 1);
	/// assert_eq!(iter.next(), Some((1, &'b')));
	///
	/// assert_eq!(iter.next_index(), 2);
	/// assert_eq!(iter.next(), None);
	/// assert_eq!(iter.next_index(), 2);
	/// ```
	#[inline]
	#[unstable(feature = "next_index", issue = "130711")]
	pub fn next_index(&self) -> usize {
	self.count
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<I> Iterator for Enumerate<I>
	where
	I: Iterator,
	{
	type Item = (usize, <I as Iterator>::Item);

	/// # Overflow Behavior
	///
	/// The method does no guarding against overflows, so enumerating more than
	/// `usize::MAX` elements either produces the wrong result or panics. If
	/// overflow checks are enabled, a panic is guaranteed.
	///
	/// # Panics
	///
	/// Might panic if the index of the element overflows a `usize`.
	#[inline]
	#[rustc_inherit_overflow_checks]
	fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
	let a = self.iter.next()?;
	let i = self.count;
	self.count += 1;
	Some((i, a))
	}

	#[inline]
	fn size_hint(&self) -> (usize, Option<usize>) {
	self.iter.size_hint()
	}

	#[inline]
	#[rustc_inherit_overflow_checks]
	fn nth(&mut self, n: usize) -> Option<(usize, I::Item)> {
	let a = self.iter.nth(n)?;
	let i = self.count + n;
	self.count = i + 1;
	Some((i, a))
	}

	#[inline]
	fn count(self) -> usize {
	self.iter.count()
	}

	#[inline]
	fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
	where
	Self: Sized,
	Fold: FnMut(Acc, Self::Item) -> R,
	R: Try<Output = Acc>,
	{
	#[inline]
	fn enumerate<'a, T, Acc, R>(
	count: &'a mut usize,
	mut fold: impl FnMut(Acc, (usize, T)) -> R + 'a,
	) -> impl FnMut(Acc, T) -> R + 'a {
	#[rustc_inherit_overflow_checks]
	move \|acc, item\| {
	let acc = fold(acc, (*count, item));
	*count += 1;
	acc
	}
	}

	self.iter.try_fold(init, enumerate(&mut self.count, fold))
	}

	#[inline]
	fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
	where
	Fold: FnMut(Acc, Self::Item) -> Acc,
	{
	#[inline]
	fn enumerate<T, Acc>(
	mut count: usize,
	mut fold: impl FnMut(Acc, (usize, T)) -> Acc,
	) -> impl FnMut(Acc, T) -> Acc {
	#[rustc_inherit_overflow_checks]
	move \|acc, item\| {
	let acc = fold(acc, (count, item));
	count += 1;
	acc
	}
	}

	self.iter.fold(init, enumerate(self.count, fold))
	}

	#[inline]
	#[rustc_inherit_overflow_checks]
	fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
	let remaining = self.iter.advance_by(n);
	let advanced = match remaining {
	Ok(()) => n,
	Err(rem) => n - rem.get(),
	};
	self.count += advanced;
	remaining
	}

	#[rustc_inherit_overflow_checks]
	#[inline]
	unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> <Self as Iterator>::Item
	where
	Self: TrustedRandomAccessNoCoerce,
	{
	// SAFETY: the caller must uphold the contract for
	// `Iterator::__iterator_get_unchecked`.
	let value = unsafe { try_get_unchecked(&mut self.iter, idx) };
	(self.count + idx, value)
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<I> DoubleEndedIterator for Enumerate<I>
	where
	I: ExactSizeIterator + DoubleEndedIterator,
	{
	#[inline]
	fn next_back(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
	let a = self.iter.next_back()?;
	let len = self.iter.len();
	// Can safely add, `ExactSizeIterator` promises that the number of
	// elements fits into a `usize`.
	Some((self.count + len, a))
	}

	#[inline]
	fn nth_back(&mut self, n: usize) -> Option<(usize, <I as Iterator>::Item)> {
	let a = self.iter.nth_back(n)?;
	let len = self.iter.len();
	// Can safely add, `ExactSizeIterator` promises that the number of
	// elements fits into a `usize`.
	Some((self.count + len, a))
	}

	#[inline]
	fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
	where
	Self: Sized,
	Fold: FnMut(Acc, Self::Item) -> R,
	R: Try<Output = Acc>,
	{
	// Can safely add and subtract the count, as `ExactSizeIterator` promises
	// that the number of elements fits into a `usize`.
	fn enumerate<T, Acc, R>(
	mut count: usize,
	mut fold: impl FnMut(Acc, (usize, T)) -> R,
	) -> impl FnMut(Acc, T) -> R {
	move \|acc, item\| {
	count -= 1;
	fold(acc, (count, item))
	}
	}

	let count = self.count + self.iter.len();
	self.iter.try_rfold(init, enumerate(count, fold))
	}

	#[inline]
	fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
	where
	Fold: FnMut(Acc, Self::Item) -> Acc,
	{
	// Can safely add and subtract the count, as `ExactSizeIterator` promises
	// that the number of elements fits into a `usize`.
	fn enumerate<T, Acc>(
	mut count: usize,
	mut fold: impl FnMut(Acc, (usize, T)) -> Acc,
	) -> impl FnMut(Acc, T) -> Acc {
	move \|acc, item\| {
	count -= 1;
	fold(acc, (count, item))
	}
	}

	let count = self.count + self.iter.len();
	self.iter.rfold(init, enumerate(count, fold))
	}

	#[inline]
	fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
	// we do not need to update the count since that only tallies the number of items
	// consumed from the front. consuming items from the back can never reduce that.
	self.iter.advance_back_by(n)
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<I> ExactSizeIterator for Enumerate<I>
	where
	I: ExactSizeIterator,
	{
	fn len(&self) -> usize {
	self.iter.len()
	}

	fn is_empty(&self) -> bool {
	self.iter.is_empty()
	}
	}

	#[doc(hidden)]
	#[unstable(feature = "trusted_random_access", issue = "none")]
	unsafe impl<I> TrustedRandomAccess for Enumerate<I> where I: TrustedRandomAccess {}

	#[doc(hidden)]
	#[unstable(feature = "trusted_random_access", issue = "none")]
	unsafe impl<I> TrustedRandomAccessNoCoerce for Enumerate<I>
	where
	I: TrustedRandomAccessNoCoerce,
	{
	const MAY_HAVE_SIDE_EFFECT: bool = I::MAY_HAVE_SIDE_EFFECT;
	}

	#[stable(feature = "fused", since = "1.26.0")]
	impl<I> FusedIterator for Enumerate<I> where I: FusedIterator {}

	#[unstable(issue = "none", feature = "trusted_fused")]
	unsafe impl<I: TrustedFused> TrustedFused for Enumerate<I> {}

	#[unstable(feature = "trusted_len", issue = "37572")]
	unsafe impl<I> TrustedLen for Enumerate<I> where I: TrustedLen {}

	#[unstable(issue = "none", feature = "inplace_iteration")]
	unsafe impl<I> SourceIter for Enumerate<I>
	where
	I: SourceIter,
	{
	type Source = I::Source;

	#[inline]
	unsafe fn as_inner(&mut self) -> &mut I::Source {
	// SAFETY: unsafe function forwarding to unsafe function with the same requirements
	unsafe { SourceIter::as_inner(&mut self.iter) }
	}
	}

	#[unstable(issue = "none", feature = "inplace_iteration")]
	unsafe impl<I: InPlaceIterable> InPlaceIterable for Enumerate<I> {
	const EXPAND_BY: Option<NonZero<usize>> = I::EXPAND_BY;
	const MERGE_BY: Option<NonZero<usize>> = I::MERGE_BY;
	}

	#[stable(feature = "default_iters", since = "1.70.0")]
	impl<I: Default> Default for Enumerate<I> {
	/// Creates an `Enumerate` iterator from the default value of `I`
	/// ```
	/// # use core::slice;
	/// # use std::iter::Enumerate;
	/// let iter: Enumerate<slice::Iter<'_, u8>> = Default::default();
	/// assert_eq!(iter.len(), 0);
	/// ```
	fn default() -> Self {
	Enumerate::new(Default::default())
	}
	}