1 use crate::fmt; 2 use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable}; 3 use crate::ops::Try; 4 5 /// An iterator that rejects elements while `predicate` returns `true`. 6 /// 7 /// This `struct` is created by the [`skip_while`] method on [`Iterator`]. See its 8 /// documentation for more. 9 /// 10 /// [`skip_while`]: Iterator::skip_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 SkipWhile<I, P> { 16 iter: I, 17 flag: bool, 18 predicate: P, 19 } 20 21 impl<I, P> SkipWhile<I, P> { new(iter: I, predicate: P) -> SkipWhile<I, P>22 pub(in crate::iter) fn new(iter: I, predicate: P) -> SkipWhile<I, P> { 23 SkipWhile { 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 SkipWhile<I, P> { fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result29 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { 30 f.debug_struct("SkipWhile").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 SkipWhile<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 fn check<'a, T>( 44 flag: &'a mut bool, 45 pred: &'a mut impl FnMut(&T) -> bool, 46 ) -> impl FnMut(&T) -> bool + 'a { 47 move |x| { 48 if *flag || !pred(x) { 49 *flag = true; 50 true 51 } else { 52 false 53 } 54 } 55 } 56 57 let flag = &mut self.flag; 58 let pred = &mut self.predicate; 59 self.iter.find(check(flag, pred)) 60 } 61 62 #[inline] size_hint(&self) -> (usize, Option<usize>)63 fn size_hint(&self) -> (usize, Option<usize>) { 64 let (_, upper) = self.iter.size_hint(); 65 (0, upper) // can't know a lower bound, due to the predicate 66 } 67 68 #[inline] try_fold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R where Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Output = Acc>,69 fn try_fold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R 70 where 71 Self: Sized, 72 Fold: FnMut(Acc, Self::Item) -> R, 73 R: Try<Output = Acc>, 74 { 75 if !self.flag { 76 match self.next() { 77 Some(v) => init = fold(init, v)?, 78 None => return try { init }, 79 } 80 } 81 self.iter.try_fold(init, fold) 82 } 83 84 #[inline] fold<Acc, Fold>(mut self, mut init: Acc, mut fold: Fold) -> Acc where Fold: FnMut(Acc, Self::Item) -> Acc,85 fn fold<Acc, Fold>(mut self, mut init: Acc, mut fold: Fold) -> Acc 86 where 87 Fold: FnMut(Acc, Self::Item) -> Acc, 88 { 89 if !self.flag { 90 match self.next() { 91 Some(v) => init = fold(init, v), 92 None => return init, 93 } 94 } 95 self.iter.fold(init, fold) 96 } 97 } 98 99 #[stable(feature = "fused", since = "1.26.0")] 100 impl<I, P> FusedIterator for SkipWhile<I, P> 101 where 102 I: FusedIterator, 103 P: FnMut(&I::Item) -> bool, 104 { 105 } 106 107 #[unstable(issue = "none", feature = "inplace_iteration")] 108 unsafe impl<P, I> SourceIter for SkipWhile<I, P> 109 where 110 I: SourceIter, 111 { 112 type Source = I::Source; 113 114 #[inline] as_inner(&mut self) -> &mut I::Source115 unsafe fn as_inner(&mut self) -> &mut I::Source { 116 // SAFETY: unsafe function forwarding to unsafe function with the same requirements 117 unsafe { SourceIter::as_inner(&mut self.iter) } 118 } 119 } 120 121 #[unstable(issue = "none", feature = "inplace_iteration")] 122 unsafe impl<I: InPlaceIterable, F> InPlaceIterable for SkipWhile<I, F> where 123 F: FnMut(&I::Item) -> bool 124 { 125 } 126