1use crate::fmt;
2use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable, TrustedFused};
3use crate::num::NonZero;
4use crate::ops::Try;
5
6/// An iterator that calls a function with a reference to each element before
7/// yielding it.
8///
9/// This `struct` is created by the [`inspect`] method on [`Iterator`]. See its
10/// documentation for more.
11///
12/// [`inspect`]: Iterator::inspect
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 Inspect<I, F> {
18 iter: I,
19 f: F,
20}
21impl<I, F> Inspect<I, F> {
22 pub(in crate::iter) fn new(iter: I, f: F) -> Inspect<I, F> {
23 Inspect { iter, f }
24 }
25}
26
27#[stable(feature = "core_impl_debug", since = "1.9.0")]
28impl<I: fmt::Debug, F> fmt::Debug for Inspect<I, F> {
29 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
30 f.debug_struct("Inspect").field(name:"iter", &self.iter).finish()
31 }
32}
33
34impl<I: Iterator, F> Inspect<I, F>
35where
36 F: FnMut(&I::Item),
37{
38 #[inline]
39 fn do_inspect(&mut self, elt: Option<I::Item>) -> Option<I::Item> {
40 if let Some(ref a: &::Item) = elt {
41 (self.f)(a);
42 }
43
44 elt
45 }
46}
47
48fn inspect_fold<T, Acc>(
49 mut f: impl FnMut(&T),
50 mut fold: impl FnMut(Acc, T) -> Acc,
51) -> impl FnMut(Acc, T) -> Acc {
52 move |acc: Acc, item: T| {
53 f(&item);
54 fold(acc, item)
55 }
56}
57
58fn inspect_try_fold<'a, T, Acc, R>(
59 f: &'a mut impl FnMut(&T),
60 mut fold: impl FnMut(Acc, T) -> R + 'a,
61) -> impl FnMut(Acc, T) -> R + 'a {
62 move |acc: Acc, item: T| {
63 f(&item);
64 fold(acc, item)
65 }
66}
67
68#[stable(feature = "rust1", since = "1.0.0")]
69impl<I: Iterator, F> Iterator for Inspect<I, F>
70where
71 F: FnMut(&I::Item),
72{
73 type Item = I::Item;
74
75 #[inline]
76 fn next(&mut self) -> Option<I::Item> {
77 let next = self.iter.next();
78 self.do_inspect(next)
79 }
80
81 #[inline]
82 fn size_hint(&self) -> (usize, Option<usize>) {
83 self.iter.size_hint()
84 }
85
86 #[inline]
87 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
88 where
89 Self: Sized,
90 Fold: FnMut(Acc, Self::Item) -> R,
91 R: Try<Output = Acc>,
92 {
93 self.iter.try_fold(init, inspect_try_fold(&mut self.f, fold))
94 }
95
96 #[inline]
97 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
98 where
99 Fold: FnMut(Acc, Self::Item) -> Acc,
100 {
101 self.iter.fold(init, inspect_fold(self.f, fold))
102 }
103}
104
105#[stable(feature = "rust1", since = "1.0.0")]
106impl<I: DoubleEndedIterator, F> DoubleEndedIterator for Inspect<I, F>
107where
108 F: FnMut(&I::Item),
109{
110 #[inline]
111 fn next_back(&mut self) -> Option<I::Item> {
112 let next = self.iter.next_back();
113 self.do_inspect(next)
114 }
115
116 #[inline]
117 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
118 where
119 Self: Sized,
120 Fold: FnMut(Acc, Self::Item) -> R,
121 R: Try<Output = Acc>,
122 {
123 self.iter.try_rfold(init, inspect_try_fold(&mut self.f, fold))
124 }
125
126 #[inline]
127 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
128 where
129 Fold: FnMut(Acc, Self::Item) -> Acc,
130 {
131 self.iter.rfold(init, inspect_fold(self.f, fold))
132 }
133}
134
135#[stable(feature = "rust1", since = "1.0.0")]
136impl<I: ExactSizeIterator, F> ExactSizeIterator for Inspect<I, F>
137where
138 F: FnMut(&I::Item),
139{
140 fn len(&self) -> usize {
141 self.iter.len()
142 }
143
144 fn is_empty(&self) -> bool {
145 self.iter.is_empty()
146 }
147}
148
149#[stable(feature = "fused", since = "1.26.0")]
150impl<I: FusedIterator, F> FusedIterator for Inspect<I, F> where F: FnMut(&I::Item) {}
151
152#[unstable(issue = "none", feature = "trusted_fused")]
153unsafe impl<I: TrustedFused, F> TrustedFused for Inspect<I, F> {}
154
155#[unstable(issue = "none", feature = "inplace_iteration")]
156unsafe impl<I, F> SourceIter for Inspect<I, F>
157where
158 I: SourceIter,
159{
160 type Source = I::Source;
161
162 #[inline]
163 unsafe fn as_inner(&mut self) -> &mut I::Source {
164 // SAFETY: unsafe function forwarding to unsafe function with the same requirements
165 unsafe { SourceIter::as_inner(&mut self.iter) }
166 }
167}
168
169#[unstable(issue = "none", feature = "inplace_iteration")]
170unsafe impl<I: InPlaceIterable, F> InPlaceIterable for Inspect<I, F> {
171 const EXPAND_BY: Option<NonZero<usize>> = I::EXPAND_BY;
172 const MERGE_BY: Option<NonZero<usize>> = I::MERGE_BY;
173}
174