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