1 use crate::fmt; 2 use crate::iter::{adapters::SourceIter, InPlaceIterable}; 3 use crate::ops::{ControlFlow, Try}; 4 5 /// An iterator that only accepts elements while `predicate` returns `Some(_)`. 6 /// 7 /// This `struct` is created by the [`map_while`] method on [`Iterator`]. See its 8 /// documentation for more. 9 /// 10 /// [`map_while`]: Iterator::map_while 11 /// [`Iterator`]: trait.Iterator.html 12 #[must_use = "iterators are lazy and do nothing unless consumed"] 13 #[stable(feature = "iter_map_while", since = "1.57.0")] 14 #[derive(Clone)] 15 pub struct MapWhile<I, P> { 16 iter: I, 17 predicate: P, 18 } 19 20 impl<I, P> MapWhile<I, P> { new(iter: I, predicate: P) -> MapWhile<I, P>21 pub(in crate::iter) fn new(iter: I, predicate: P) -> MapWhile<I, P> { 22 MapWhile { iter, predicate } 23 } 24 } 25 26 #[stable(feature = "iter_map_while", since = "1.57.0")] 27 impl<I: fmt::Debug, P> fmt::Debug for MapWhile<I, P> { fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result28 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { 29 f.debug_struct("MapWhile").field("iter", &self.iter).finish() 30 } 31 } 32 33 #[stable(feature = "iter_map_while", since = "1.57.0")] 34 impl<B, I: Iterator, P> Iterator for MapWhile<I, P> 35 where 36 P: FnMut(I::Item) -> Option<B>, 37 { 38 type Item = B; 39 40 #[inline] next(&mut self) -> Option<B>41 fn next(&mut self) -> Option<B> { 42 let x = self.iter.next()?; 43 (self.predicate)(x) 44 } 45 46 #[inline] size_hint(&self) -> (usize, Option<usize>)47 fn size_hint(&self) -> (usize, Option<usize>) { 48 let (_, upper) = self.iter.size_hint(); 49 (0, upper) // can't know a lower bound, due to the predicate 50 } 51 52 #[inline] try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Output = Acc>,53 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R 54 where 55 Self: Sized, 56 Fold: FnMut(Acc, Self::Item) -> R, 57 R: Try<Output = Acc>, 58 { 59 let Self { iter, predicate } = self; 60 iter.try_fold(init, |acc, x| match predicate(x) { 61 Some(item) => ControlFlow::from_try(fold(acc, item)), 62 None => ControlFlow::Break(try { acc }), 63 }) 64 .into_try() 65 } 66 67 #[inline] fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc where Self: Sized, Fold: FnMut(Acc, Self::Item) -> Acc,68 fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc 69 where 70 Self: Sized, 71 Fold: FnMut(Acc, Self::Item) -> Acc, 72 { 73 #[inline] 74 fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> { 75 move |acc, x| Ok(f(acc, x)) 76 } 77 78 self.try_fold(init, ok(fold)).unwrap() 79 } 80 } 81 82 #[unstable(issue = "none", feature = "inplace_iteration")] 83 unsafe impl<I, P> SourceIter for MapWhile<I, P> 84 where 85 I: SourceIter, 86 { 87 type Source = I::Source; 88 89 #[inline] as_inner(&mut self) -> &mut I::Source90 unsafe fn as_inner(&mut self) -> &mut I::Source { 91 // SAFETY: unsafe function forwarding to unsafe function with the same requirements 92 unsafe { SourceIter::as_inner(&mut self.iter) } 93 } 94 } 95 96 #[unstable(issue = "none", feature = "inplace_iteration")] 97 unsafe impl<B, I: InPlaceIterable, P> InPlaceIterable for MapWhile<I, P> where 98 P: FnMut(I::Item) -> Option<B> 99 { 100 } 101