1 | use crate::fmt; |
2 | use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable, TrustedFused}; |
3 | use crate::num::NonZero; |
4 | use crate::ops::{ControlFlow, Try}; |
5 | |
6 | /// An iterator that only accepts elements while `predicate` returns `true`. |
7 | /// |
8 | /// This `struct` is created by the [`take_while`] method on [`Iterator`]. See its |
9 | /// documentation for more. |
10 | /// |
11 | /// [`take_while`]: Iterator::take_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 TakeWhile<I, P> { |
17 | iter: I, |
18 | flag: bool, |
19 | predicate: P, |
20 | } |
21 | |
22 | impl<I, P> TakeWhile<I, P> { |
23 | pub(in crate::iter) fn new(iter: I, predicate: P) -> TakeWhile<I, P> { |
24 | TakeWhile { 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 TakeWhile<I, P> { |
30 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
31 | f.debug_struct("TakeWhile" ).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 TakeWhile<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 | if self.flag { |
45 | None |
46 | } else { |
47 | let x = self.iter.next()?; |
48 | if (self.predicate)(&x) { |
49 | Some(x) |
50 | } else { |
51 | self.flag = true; |
52 | None |
53 | } |
54 | } |
55 | } |
56 | |
57 | #[inline ] |
58 | fn size_hint(&self) -> (usize, Option<usize>) { |
59 | if self.flag { |
60 | (0, Some(0)) |
61 | } else { |
62 | let (_, upper) = self.iter.size_hint(); |
63 | (0, upper) // can't know a lower bound, due to the predicate |
64 | } |
65 | } |
66 | |
67 | #[inline ] |
68 | fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R |
69 | where |
70 | Self: Sized, |
71 | Fold: FnMut(Acc, Self::Item) -> R, |
72 | R: Try<Output = Acc>, |
73 | { |
74 | fn check<'a, T, Acc, R: Try<Output = Acc>>( |
75 | flag: &'a mut bool, |
76 | p: &'a mut impl FnMut(&T) -> bool, |
77 | mut fold: impl FnMut(Acc, T) -> R + 'a, |
78 | ) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> + 'a { |
79 | move |acc, x| { |
80 | if p(&x) { |
81 | ControlFlow::from_try(fold(acc, x)) |
82 | } else { |
83 | *flag = true; |
84 | ControlFlow::Break(try { acc }) |
85 | } |
86 | } |
87 | } |
88 | |
89 | if self.flag { |
90 | try { init } |
91 | } else { |
92 | let flag = &mut self.flag; |
93 | let p = &mut self.predicate; |
94 | self.iter.try_fold(init, check(flag, p, fold)).into_try() |
95 | } |
96 | } |
97 | |
98 | impl_fold_via_try_fold! { fold -> try_fold } |
99 | } |
100 | |
101 | #[stable (feature = "fused" , since = "1.26.0" )] |
102 | impl<I, P> FusedIterator for TakeWhile<I, P> |
103 | where |
104 | I: FusedIterator, |
105 | P: FnMut(&I::Item) -> bool, |
106 | { |
107 | } |
108 | |
109 | #[unstable (issue = "none" , feature = "trusted_fused" )] |
110 | unsafe impl<I: TrustedFused, P> TrustedFused for TakeWhile<I, P> {} |
111 | |
112 | #[unstable (issue = "none" , feature = "inplace_iteration" )] |
113 | unsafe impl<P, I> SourceIter for TakeWhile<I, P> |
114 | where |
115 | I: SourceIter, |
116 | { |
117 | type Source = I::Source; |
118 | |
119 | #[inline ] |
120 | unsafe fn as_inner(&mut self) -> &mut I::Source { |
121 | // SAFETY: unsafe function forwarding to unsafe function with the same requirements |
122 | unsafe { SourceIter::as_inner(&mut self.iter) } |
123 | } |
124 | } |
125 | |
126 | #[unstable (issue = "none" , feature = "inplace_iteration" )] |
127 | unsafe impl<I: InPlaceIterable, F> InPlaceIterable for TakeWhile<I, F> { |
128 | const EXPAND_BY: Option<NonZero<usize>> = I::EXPAND_BY; |
129 | const MERGE_BY: Option<NonZero<usize>> = I::MERGE_BY; |
130 | } |
131 | |