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