1 use crate::fmt;
2 use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
3 use crate::ops::Try;
4
5 /// An iterator that calls a function with a reference to each element before
6 /// yielding it.
7 ///
8 /// This `struct` is created by the [`inspect`] method on [`Iterator`]. See its
9 /// documentation for more.
10 ///
11 /// [`inspect`]: Iterator::inspect
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 Inspect<I, F> {
17 iter: I,
18 f: F,
19 }
20 impl<I, F> Inspect<I, F> {
new(iter: I, f: F) -> Inspect<I, F>21 pub(in crate::iter) fn new(iter: I, f: F) -> Inspect<I, F> {
22 Inspect { iter, f }
23 }
24 }
25
26 #[stable(feature = "core_impl_debug", since = "1.9.0")]
27 impl<I: fmt::Debug, F> fmt::Debug for Inspect<I, F> {
fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result28 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
29 f.debug_struct("Inspect").field("iter", &self.iter).finish()
30 }
31 }
32
33 impl<I: Iterator, F> Inspect<I, F>
34 where
35 F: FnMut(&I::Item),
36 {
37 #[inline]
do_inspect(&mut self, elt: Option<I::Item>) -> Option<I::Item>38 fn do_inspect(&mut self, elt: Option<I::Item>) -> Option<I::Item> {
39 if let Some(ref a) = elt {
40 (self.f)(a);
41 }
42
43 elt
44 }
45 }
46
inspect_fold<T, Acc>( mut f: impl FnMut(&T), mut fold: impl FnMut(Acc, T) -> Acc, ) -> impl FnMut(Acc, T) -> Acc47 fn inspect_fold<T, Acc>(
48 mut f: impl FnMut(&T),
49 mut fold: impl FnMut(Acc, T) -> Acc,
50 ) -> impl FnMut(Acc, T) -> Acc {
51 move |acc, item| {
52 f(&item);
53 fold(acc, item)
54 }
55 }
56
inspect_try_fold<'a, T, Acc, R>( f: &'a mut impl FnMut(&T), mut fold: impl FnMut(Acc, T) -> R + 'a, ) -> impl FnMut(Acc, T) -> R + 'a57 fn inspect_try_fold<'a, T, Acc, R>(
58 f: &'a mut impl FnMut(&T),
59 mut fold: impl FnMut(Acc, T) -> R + 'a,
60 ) -> impl FnMut(Acc, T) -> R + 'a {
61 move |acc, item| {
62 f(&item);
63 fold(acc, item)
64 }
65 }
66
67 #[stable(feature = "rust1", since = "1.0.0")]
68 impl<I: Iterator, F> Iterator for Inspect<I, F>
69 where
70 F: FnMut(&I::Item),
71 {
72 type Item = I::Item;
73
74 #[inline]
next(&mut self) -> Option<I::Item>75 fn next(&mut self) -> Option<I::Item> {
76 let next = self.iter.next();
77 self.do_inspect(next)
78 }
79
80 #[inline]
size_hint(&self) -> (usize, Option<usize>)81 fn size_hint(&self) -> (usize, Option<usize>) {
82 self.iter.size_hint()
83 }
84
85 #[inline]
try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Output = Acc>,86 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
87 where
88 Self: Sized,
89 Fold: FnMut(Acc, Self::Item) -> R,
90 R: Try<Output = Acc>,
91 {
92 self.iter.try_fold(init, inspect_try_fold(&mut self.f, fold))
93 }
94
95 #[inline]
fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc where Fold: FnMut(Acc, Self::Item) -> Acc,96 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
97 where
98 Fold: FnMut(Acc, Self::Item) -> Acc,
99 {
100 self.iter.fold(init, inspect_fold(self.f, fold))
101 }
102 }
103
104 #[stable(feature = "rust1", since = "1.0.0")]
105 impl<I: DoubleEndedIterator, F> DoubleEndedIterator for Inspect<I, F>
106 where
107 F: FnMut(&I::Item),
108 {
109 #[inline]
next_back(&mut self) -> Option<I::Item>110 fn next_back(&mut self) -> Option<I::Item> {
111 let next = self.iter.next_back();
112 self.do_inspect(next)
113 }
114
115 #[inline]
try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Output = Acc>,116 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
117 where
118 Self: Sized,
119 Fold: FnMut(Acc, Self::Item) -> R,
120 R: Try<Output = Acc>,
121 {
122 self.iter.try_rfold(init, inspect_try_fold(&mut self.f, fold))
123 }
124
125 #[inline]
rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc where Fold: FnMut(Acc, Self::Item) -> Acc,126 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
127 where
128 Fold: FnMut(Acc, Self::Item) -> Acc,
129 {
130 self.iter.rfold(init, inspect_fold(self.f, fold))
131 }
132 }
133
134 #[stable(feature = "rust1", since = "1.0.0")]
135 impl<I: ExactSizeIterator, F> ExactSizeIterator for Inspect<I, F>
136 where
137 F: FnMut(&I::Item),
138 {
len(&self) -> usize139 fn len(&self) -> usize {
140 self.iter.len()
141 }
142
is_empty(&self) -> bool143 fn is_empty(&self) -> bool {
144 self.iter.is_empty()
145 }
146 }
147
148 #[stable(feature = "fused", since = "1.26.0")]
149 impl<I: FusedIterator, F> FusedIterator for Inspect<I, F> where F: FnMut(&I::Item) {}
150
151 #[unstable(issue = "none", feature = "inplace_iteration")]
152 unsafe impl<I, F> SourceIter for Inspect<I, F>
153 where
154 I: SourceIter,
155 {
156 type Source = I::Source;
157
158 #[inline]
as_inner(&mut self) -> &mut I::Source159 unsafe fn as_inner(&mut self) -> &mut I::Source {
160 // SAFETY: unsafe function forwarding to unsafe function with the same requirements
161 unsafe { SourceIter::as_inner(&mut self.iter) }
162 }
163 }
164
165 #[unstable(issue = "none", feature = "inplace_iteration")]
166 unsafe impl<I: InPlaceIterable, F> InPlaceIterable for Inspect<I, F> where F: FnMut(&I::Item) {}
167