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