1 use crate::fmt; 2 use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable}; 3 use crate::ops::{ControlFlow, Try}; 4 5 /// An iterator that only accepts elements while `predicate` returns `true`. 6 /// 7 /// This `struct` is created by the [`take_while`] method on [`Iterator`]. See its 8 /// documentation for more. 9 /// 10 /// [`take_while`]: Iterator::take_while 11 /// [`Iterator`]: trait.Iterator.html 12 #[must_use = "iterators are lazy and do nothing unless consumed"] 13 #[stable(feature = "rust1", since = "1.0.0")] 14 #[derive(Clone)] 15 pub struct TakeWhile<I, P> { 16 iter: I, 17 flag: bool, 18 predicate: P, 19 } 20 21 impl<I, P> TakeWhile<I, P> { new(iter: I, predicate: P) -> TakeWhile<I, P>22 pub(in crate::iter) fn new(iter: I, predicate: P) -> TakeWhile<I, P> { 23 TakeWhile { iter, flag: false, predicate } 24 } 25 } 26 27 #[stable(feature = "core_impl_debug", since = "1.9.0")] 28 impl<I: fmt::Debug, P> fmt::Debug for TakeWhile<I, P> { fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result29 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { 30 f.debug_struct("TakeWhile").field("iter", &self.iter).field("flag", &self.flag).finish() 31 } 32 } 33 34 #[stable(feature = "rust1", since = "1.0.0")] 35 impl<I: Iterator, P> Iterator for TakeWhile<I, P> 36 where 37 P: FnMut(&I::Item) -> bool, 38 { 39 type Item = I::Item; 40 41 #[inline] next(&mut self) -> Option<I::Item>42 fn next(&mut self) -> Option<I::Item> { 43 if self.flag { 44 None 45 } else { 46 let x = self.iter.next()?; 47 if (self.predicate)(&x) { 48 Some(x) 49 } else { 50 self.flag = true; 51 None 52 } 53 } 54 } 55 56 #[inline] size_hint(&self) -> (usize, Option<usize>)57 fn size_hint(&self) -> (usize, Option<usize>) { 58 if self.flag { 59 (0, Some(0)) 60 } else { 61 let (_, upper) = self.iter.size_hint(); 62 (0, upper) // can't know a lower bound, due to the predicate 63 } 64 } 65 66 #[inline] 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>,67 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R 68 where 69 Self: Sized, 70 Fold: FnMut(Acc, Self::Item) -> R, 71 R: Try<Output = Acc>, 72 { 73 fn check<'a, T, Acc, R: Try<Output = Acc>>( 74 flag: &'a mut bool, 75 p: &'a mut impl FnMut(&T) -> bool, 76 mut fold: impl FnMut(Acc, T) -> R + 'a, 77 ) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> + 'a { 78 move |acc, x| { 79 if p(&x) { 80 ControlFlow::from_try(fold(acc, x)) 81 } else { 82 *flag = true; 83 ControlFlow::Break(try { acc }) 84 } 85 } 86 } 87 88 if self.flag { 89 try { init } 90 } else { 91 let flag = &mut self.flag; 92 let p = &mut self.predicate; 93 self.iter.try_fold(init, check(flag, p, fold)).into_try() 94 } 95 } 96 97 #[inline] fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc where Self: Sized, Fold: FnMut(Acc, Self::Item) -> Acc,98 fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc 99 where 100 Self: Sized, 101 Fold: FnMut(Acc, Self::Item) -> Acc, 102 { 103 #[inline] 104 fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> { 105 move |acc, x| Ok(f(acc, x)) 106 } 107 108 self.try_fold(init, ok(fold)).unwrap() 109 } 110 } 111 112 #[stable(feature = "fused", since = "1.26.0")] 113 impl<I, P> FusedIterator for TakeWhile<I, P> 114 where 115 I: FusedIterator, 116 P: FnMut(&I::Item) -> bool, 117 { 118 } 119 120 #[unstable(issue = "none", feature = "inplace_iteration")] 121 unsafe impl<P, I> SourceIter for TakeWhile<I, P> 122 where 123 I: SourceIter, 124 { 125 type Source = I::Source; 126 127 #[inline] as_inner(&mut self) -> &mut I::Source128 unsafe fn as_inner(&mut self) -> &mut I::Source { 129 // SAFETY: unsafe function forwarding to unsafe function with the same requirements 130 unsafe { SourceIter::as_inner(&mut self.iter) } 131 } 132 } 133 134 #[unstable(issue = "none", feature = "inplace_iteration")] 135 unsafe impl<I: InPlaceIterable, F> InPlaceIterable for TakeWhile<I, F> where 136 F: FnMut(&I::Item) -> bool 137 { 138 } 139