1use crate::fmt;
2use crate::iter::adapters::zip::try_get_unchecked;
3use crate::iter::adapters::{SourceIter, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
4use crate::iter::{FusedIterator, InPlaceIterable, TrustedFused, TrustedLen, UncheckedIterator};
5use crate::num::NonZero;
6use crate::ops::Try;
7
8/// An iterator that maps the values of `iter` with `f`.
9///
10/// This `struct` is created by the [`map`] method on [`Iterator`]. See its
11/// documentation for more.
12///
13/// [`map`]: Iterator::map
14/// [`Iterator`]: trait.Iterator.html
15///
16/// # Notes about side effects
17///
18/// The [`map`] iterator implements [`DoubleEndedIterator`], meaning that
19/// you can also [`map`] backwards:
20///
21/// ```rust
22/// let v: Vec<i32> = [1, 2, 3].into_iter().map(|x| x + 1).rev().collect();
23///
24/// assert_eq!(v, [4, 3, 2]);
25/// ```
26///
27/// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html
28///
29/// But if your closure has state, iterating backwards may act in a way you do
30/// not expect. Let's go through an example. First, in the forward direction:
31///
32/// ```rust
33/// let mut c = 0;
34///
35/// for pair in ['a', 'b', 'c'].into_iter()
36/// .map(|letter| { c += 1; (letter, c) }) {
37/// println!("{pair:?}");
38/// }
39/// ```
40///
41/// This will print `('a', 1), ('b', 2), ('c', 3)`.
42///
43/// Now consider this twist where we add a call to `rev`. This version will
44/// print `('c', 1), ('b', 2), ('a', 3)`. Note that the letters are reversed,
45/// but the values of the counter still go in order. This is because `map()` is
46/// still being called lazily on each item, but we are popping items off the
47/// back of the vector now, instead of shifting them from the front.
48///
49/// ```rust
50/// let mut c = 0;
51///
52/// for pair in ['a', 'b', 'c'].into_iter()
53/// .map(|letter| { c += 1; (letter, c) })
54/// .rev() {
55/// println!("{pair:?}");
56/// }
57/// ```
58#[must_use = "iterators are lazy and do nothing unless consumed"]
59#[stable(feature = "rust1", since = "1.0.0")]
60#[derive(Clone)]
61pub struct Map<I, F> {
62 // Used for `SplitWhitespace` and `SplitAsciiWhitespace` `as_str` methods
63 pub(crate) iter: I,
64 f: F,
65}
66
67impl<I, F> Map<I, F> {
68 pub(in crate::iter) fn new(iter: I, f: F) -> Map<I, F> {
69 Map { iter, f }
70 }
71
72 pub(crate) fn into_inner(self) -> I {
73 self.iter
74 }
75}
76
77#[stable(feature = "core_impl_debug", since = "1.9.0")]
78impl<I: fmt::Debug, F> fmt::Debug for Map<I, F> {
79 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
80 f.debug_struct("Map").field(name:"iter", &self.iter).finish()
81 }
82}
83
84fn map_fold<T, B, Acc>(
85 mut f: impl FnMut(T) -> B,
86 mut g: impl FnMut(Acc, B) -> Acc,
87) -> impl FnMut(Acc, T) -> Acc {
88 move |acc: Acc, elt: T| g(acc, f(elt))
89}
90
91fn map_try_fold<'a, T, B, Acc, R>(
92 f: &'a mut impl FnMut(T) -> B,
93 mut g: impl FnMut(Acc, B) -> R + 'a,
94) -> impl FnMut(Acc, T) -> R + 'a {
95 move |acc: Acc, elt: T| g(acc, f(elt))
96}
97
98#[stable(feature = "rust1", since = "1.0.0")]
99impl<B, I: Iterator, F> Iterator for Map<I, F>
100where
101 F: FnMut(I::Item) -> B,
102{
103 type Item = B;
104
105 #[inline]
106 fn next(&mut self) -> Option<B> {
107 self.iter.next().map(&mut self.f)
108 }
109
110 #[inline]
111 fn size_hint(&self) -> (usize, Option<usize>) {
112 self.iter.size_hint()
113 }
114
115 fn try_fold<Acc, G, R>(&mut self, init: Acc, g: G) -> R
116 where
117 Self: Sized,
118 G: FnMut(Acc, Self::Item) -> R,
119 R: Try<Output = Acc>,
120 {
121 self.iter.try_fold(init, map_try_fold(&mut self.f, g))
122 }
123
124 fn fold<Acc, G>(self, init: Acc, g: G) -> Acc
125 where
126 G: FnMut(Acc, Self::Item) -> Acc,
127 {
128 self.iter.fold(init, map_fold(self.f, g))
129 }
130
131 #[inline]
132 unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> B
133 where
134 Self: TrustedRandomAccessNoCoerce,
135 {
136 // SAFETY: the caller must uphold the contract for
137 // `Iterator::__iterator_get_unchecked`.
138 unsafe { (self.f)(try_get_unchecked(&mut self.iter, idx)) }
139 }
140}
141
142#[stable(feature = "rust1", since = "1.0.0")]
143impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for Map<I, F>
144where
145 F: FnMut(I::Item) -> B,
146{
147 #[inline]
148 fn next_back(&mut self) -> Option<B> {
149 self.iter.next_back().map(&mut self.f)
150 }
151
152 fn try_rfold<Acc, G, R>(&mut self, init: Acc, g: G) -> R
153 where
154 Self: Sized,
155 G: FnMut(Acc, Self::Item) -> R,
156 R: Try<Output = Acc>,
157 {
158 self.iter.try_rfold(init, f:map_try_fold(&mut self.f, g))
159 }
160
161 fn rfold<Acc, G>(self, init: Acc, g: G) -> Acc
162 where
163 G: FnMut(Acc, Self::Item) -> Acc,
164 {
165 self.iter.rfold(init, f:map_fold(self.f, g))
166 }
167}
168
169#[stable(feature = "rust1", since = "1.0.0")]
170impl<B, I: ExactSizeIterator, F> ExactSizeIterator for Map<I, F>
171where
172 F: FnMut(I::Item) -> B,
173{
174 fn len(&self) -> usize {
175 self.iter.len()
176 }
177
178 fn is_empty(&self) -> bool {
179 self.iter.is_empty()
180 }
181}
182
183#[stable(feature = "fused", since = "1.26.0")]
184impl<B, I: FusedIterator, F> FusedIterator for Map<I, F> where F: FnMut(I::Item) -> B {}
185
186#[unstable(issue = "none", feature = "trusted_fused")]
187unsafe impl<I: TrustedFused, F> TrustedFused for Map<I, F> {}
188
189#[unstable(feature = "trusted_len", issue = "37572")]
190unsafe impl<B, I, F> TrustedLen for Map<I, F>
191where
192 I: TrustedLen,
193 F: FnMut(I::Item) -> B,
194{
195}
196
197impl<B, I, F> UncheckedIterator for Map<I, F>
198where
199 I: UncheckedIterator,
200 F: FnMut(I::Item) -> B,
201{
202 unsafe fn next_unchecked(&mut self) -> B {
203 // SAFETY: `Map` is 1:1 with the inner iterator, so if the caller promised
204 // that there's an element left, the inner iterator has one too.
205 let item: ::Item = unsafe { self.iter.next_unchecked() };
206 (self.f)(item)
207 }
208}
209
210#[doc(hidden)]
211#[unstable(feature = "trusted_random_access", issue = "none")]
212unsafe impl<I, F> TrustedRandomAccess for Map<I, F> where I: TrustedRandomAccess {}
213
214#[doc(hidden)]
215#[unstable(feature = "trusted_random_access", issue = "none")]
216unsafe impl<I, F> TrustedRandomAccessNoCoerce for Map<I, F>
217where
218 I: TrustedRandomAccessNoCoerce,
219{
220 const MAY_HAVE_SIDE_EFFECT: bool = true;
221}
222
223#[unstable(issue = "none", feature = "inplace_iteration")]
224unsafe impl<I, F> SourceIter for Map<I, F>
225where
226 I: SourceIter,
227{
228 type Source = I::Source;
229
230 #[inline]
231 unsafe fn as_inner(&mut self) -> &mut I::Source {
232 // SAFETY: unsafe function forwarding to unsafe function with the same requirements
233 unsafe { SourceIter::as_inner(&mut self.iter) }
234 }
235}
236
237#[unstable(issue = "none", feature = "inplace_iteration")]
238unsafe impl<I: InPlaceIterable, F> InPlaceIterable for Map<I, F> {
239 const EXPAND_BY: Option<NonZero<usize>> = I::EXPAND_BY;
240 const MERGE_BY: Option<NonZero<usize>> = I::MERGE_BY;
241}
242