213 lines
5.8 KiB
Rust
213 lines
5.8 KiB
Rust
use crate::fmt;
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use crate::iter::adapters::{zip::try_get_unchecked, SourceIter, TrustedRandomAccess};
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use crate::iter::{FusedIterator, InPlaceIterable, TrustedLen};
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use crate::ops::Try;
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/// An iterator that maps the values of `iter` with `f`.
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///
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/// This `struct` is created by the [`map`] method on [`Iterator`]. See its
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/// documentation for more.
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///
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/// [`map`]: Iterator::map
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/// [`Iterator`]: trait.Iterator.html
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///
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/// # Notes about side effects
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///
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/// The [`map`] iterator implements [`DoubleEndedIterator`], meaning that
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/// you can also [`map`] backwards:
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///
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/// ```rust
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/// let v: Vec<i32> = vec![1, 2, 3].into_iter().map(|x| x + 1).rev().collect();
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///
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/// assert_eq!(v, [4, 3, 2]);
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/// ```
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///
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/// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html
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///
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/// But if your closure has state, iterating backwards may act in a way you do
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/// not expect. Let's go through an example. First, in the forward direction:
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///
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/// ```rust
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/// let mut c = 0;
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///
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/// for pair in vec!['a', 'b', 'c'].into_iter()
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/// .map(|letter| { c += 1; (letter, c) }) {
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/// println!("{:?}", pair);
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/// }
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/// ```
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///
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/// This will print "('a', 1), ('b', 2), ('c', 3)".
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///
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/// Now consider this twist where we add a call to `rev`. This version will
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/// print `('c', 1), ('b', 2), ('a', 3)`. Note that the letters are reversed,
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/// but the values of the counter still go in order. This is because `map()` is
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/// still being called lazily on each item, but we are popping items off the
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/// back of the vector now, instead of shifting them from the front.
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///
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/// ```rust
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/// let mut c = 0;
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///
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/// for pair in vec!['a', 'b', 'c'].into_iter()
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/// .map(|letter| { c += 1; (letter, c) })
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/// .rev() {
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/// println!("{:?}", pair);
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/// }
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/// ```
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#[must_use = "iterators are lazy and do nothing unless consumed"]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[derive(Clone)]
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pub struct Map<I, F> {
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// Used for `SplitWhitespace` and `SplitAsciiWhitespace` `as_str` methods
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pub(crate) iter: I,
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f: F,
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}
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impl<I, F> Map<I, F> {
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pub(in crate::iter) fn new(iter: I, f: F) -> Map<I, F> {
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Map { iter, f }
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}
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}
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#[stable(feature = "core_impl_debug", since = "1.9.0")]
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impl<I: fmt::Debug, F> fmt::Debug for Map<I, F> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_struct("Map").field("iter", &self.iter).finish()
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}
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}
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fn map_fold<T, B, Acc>(
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mut f: impl FnMut(T) -> B,
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mut g: impl FnMut(Acc, B) -> Acc,
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) -> impl FnMut(Acc, T) -> Acc {
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move |acc, elt| g(acc, f(elt))
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}
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fn map_try_fold<'a, T, B, Acc, R>(
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f: &'a mut impl FnMut(T) -> B,
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mut g: impl FnMut(Acc, B) -> R + 'a,
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) -> impl FnMut(Acc, T) -> R + 'a {
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move |acc, elt| g(acc, f(elt))
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<B, I: Iterator, F> Iterator for Map<I, F>
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where
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F: FnMut(I::Item) -> B,
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{
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type Item = B;
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#[inline]
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fn next(&mut self) -> Option<B> {
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self.iter.next().map(&mut self.f)
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}
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#[inline]
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fn size_hint(&self) -> (usize, Option<usize>) {
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self.iter.size_hint()
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}
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fn try_fold<Acc, G, R>(&mut self, init: Acc, g: G) -> R
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where
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Self: Sized,
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G: FnMut(Acc, Self::Item) -> R,
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R: Try<Ok = Acc>,
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{
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self.iter.try_fold(init, map_try_fold(&mut self.f, g))
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}
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fn fold<Acc, G>(self, init: Acc, g: G) -> Acc
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where
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G: FnMut(Acc, Self::Item) -> Acc,
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{
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self.iter.fold(init, map_fold(self.f, g))
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}
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unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> B
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where
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Self: TrustedRandomAccess,
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{
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// SAFETY: the caller must uphold the contract for
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// `Iterator::__iterator_get_unchecked`.
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unsafe { (self.f)(try_get_unchecked(&mut self.iter, idx)) }
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for Map<I, F>
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where
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F: FnMut(I::Item) -> B,
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{
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#[inline]
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fn next_back(&mut self) -> Option<B> {
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self.iter.next_back().map(&mut self.f)
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}
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fn try_rfold<Acc, G, R>(&mut self, init: Acc, g: G) -> R
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where
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Self: Sized,
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G: FnMut(Acc, Self::Item) -> R,
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R: Try<Ok = Acc>,
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{
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self.iter.try_rfold(init, map_try_fold(&mut self.f, g))
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}
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fn rfold<Acc, G>(self, init: Acc, g: G) -> Acc
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where
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G: FnMut(Acc, Self::Item) -> Acc,
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{
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self.iter.rfold(init, map_fold(self.f, g))
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<B, I: ExactSizeIterator, F> ExactSizeIterator for Map<I, F>
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where
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F: FnMut(I::Item) -> B,
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{
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fn len(&self) -> usize {
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self.iter.len()
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}
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fn is_empty(&self) -> bool {
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self.iter.is_empty()
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}
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}
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#[stable(feature = "fused", since = "1.26.0")]
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impl<B, I: FusedIterator, F> FusedIterator for Map<I, F> where F: FnMut(I::Item) -> B {}
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#[unstable(feature = "trusted_len", issue = "37572")]
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unsafe impl<B, I, F> TrustedLen for Map<I, F>
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where
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I: TrustedLen,
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F: FnMut(I::Item) -> B,
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{
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}
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#[doc(hidden)]
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#[unstable(feature = "trusted_random_access", issue = "none")]
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unsafe impl<I, F> TrustedRandomAccess for Map<I, F>
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where
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I: TrustedRandomAccess,
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{
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const MAY_HAVE_SIDE_EFFECT: bool = true;
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}
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#[unstable(issue = "none", feature = "inplace_iteration")]
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unsafe impl<S: Iterator, B, I: Iterator, F> SourceIter for Map<I, F>
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where
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F: FnMut(I::Item) -> B,
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I: SourceIter<Source = S>,
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{
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type Source = S;
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#[inline]
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unsafe fn as_inner(&mut self) -> &mut S {
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// SAFETY: unsafe function forwarding to unsafe function with the same requirements
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unsafe { SourceIter::as_inner(&mut self.iter) }
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}
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}
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#[unstable(issue = "none", feature = "inplace_iteration")]
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unsafe impl<B, I: InPlaceIterable, F> InPlaceIterable for Map<I, F> where F: FnMut(I::Item) -> B {}
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