2 cmp, iter::FusedIterator, iter::InPlaceIterable, iter::TrustedLen, ops::ControlFlow, ops::Try,
7 /// An iterator that only iterates over the first `n` iterations of `iter`.
9 /// This `struct` is created by the [`take`] method on [`Iterator`]. See its
10 /// documentation for more.
12 /// [`take`]: Iterator::take
13 /// [`Iterator`]: trait.Iterator.html
14 #[derive(Clone, Debug)]
15 #[must_use = "iterators are lazy and do nothing unless consumed"]
16 #[stable(feature = "rust1", since = "1.0.0")]
23 pub(in crate::iter) fn new(iter: I, n: usize) -> Take<I> {
28 #[stable(feature = "rust1", since = "1.0.0")]
29 impl<I> Iterator for Take<I>
33 type Item = <I as Iterator>::Item;
36 fn next(&mut self) -> Option<<I as Iterator>::Item> {
46 fn nth(&mut self, n: usize) -> Option<I::Item> {
52 self.iter.nth(self.n - 1);
60 fn size_hint(&self) -> (usize, Option<usize>) {
65 let (lower, upper) = self.iter.size_hint();
67 let lower = cmp::min(lower, self.n);
69 let upper = match upper {
70 Some(x) if x < self.n => Some(x),
78 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
81 Fold: FnMut(Acc, Self::Item) -> R,
84 fn check<'a, T, Acc, R: Try<Ok = Acc>>(
86 mut fold: impl FnMut(Acc, T) -> R + 'a,
87 ) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> + 'a {
91 if *n == 0 { ControlFlow::Break(r) } else { ControlFlow::from_try(r) }
99 self.iter.try_fold(init, check(n, fold)).into_try()
104 fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
107 Fold: FnMut(Acc, Self::Item) -> Acc,
110 fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
111 move |acc, x| Ok(f(acc, x))
114 self.try_fold(init, ok(fold)).unwrap()
118 #[unstable(issue = "none", feature = "inplace_iteration")]
119 unsafe impl<S: Iterator, I: Iterator> SourceIter for Take<I>
121 I: SourceIter<Source = S>,
126 unsafe fn as_inner(&mut self) -> &mut S {
127 // SAFETY: unsafe function forwarding to unsafe function with the same requirements
128 unsafe { SourceIter::as_inner(&mut self.iter) }
132 #[unstable(issue = "none", feature = "inplace_iteration")]
133 unsafe impl<I: InPlaceIterable> InPlaceIterable for Take<I> {}
135 #[stable(feature = "double_ended_take_iterator", since = "1.38.0")]
136 impl<I> DoubleEndedIterator for Take<I>
138 I: DoubleEndedIterator + ExactSizeIterator,
141 fn next_back(&mut self) -> Option<Self::Item> {
147 self.iter.nth_back(self.iter.len().saturating_sub(n))
152 fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
153 let len = self.iter.len();
155 let m = len.saturating_sub(self.n) + n;
157 self.iter.nth_back(m)
160 self.iter.nth_back(len - 1);
167 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
170 Fold: FnMut(Acc, Self::Item) -> R,
176 let len = self.iter.len();
177 if len > self.n && self.iter.nth_back(len - self.n - 1).is_none() {
180 self.iter.try_rfold(init, fold)
186 fn rfold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
189 Fold: FnMut(Acc, Self::Item) -> Acc,
194 let len = self.iter.len();
195 if len > self.n && self.iter.nth_back(len - self.n - 1).is_none() {
198 self.iter.rfold(init, fold)
204 #[stable(feature = "rust1", since = "1.0.0")]
205 impl<I> ExactSizeIterator for Take<I> where I: ExactSizeIterator {}
207 #[stable(feature = "fused", since = "1.26.0")]
208 impl<I> FusedIterator for Take<I> where I: FusedIterator {}
210 #[unstable(feature = "trusted_len", issue = "37572")]
211 unsafe impl<I: TrustedLen> TrustedLen for Take<I> {}