1 | use crate::iter::adapters::{ |
2 | zip::try_get_unchecked, SourceIter, TrustedRandomAccess, TrustedRandomAccessNoCoerce, |
3 | }; |
4 | use crate::iter::{FusedIterator, InPlaceIterable, TrustedFused, TrustedLen}; |
5 | use crate::num::NonZero; |
6 | use crate::ops::Try; |
7 | |
8 | /// An iterator that yields the current count and the element during iteration. |
9 | /// |
10 | /// This `struct` is created by the [`enumerate`] method on [`Iterator`]. See its |
11 | /// documentation for more. |
12 | /// |
13 | /// [`enumerate`]: Iterator::enumerate |
14 | /// [`Iterator`]: trait.Iterator.html |
15 | #[derive (Clone, Debug)] |
16 | #[must_use = "iterators are lazy and do nothing unless consumed" ] |
17 | #[stable (feature = "rust1" , since = "1.0.0" )] |
18 | #[cfg_attr (not(test), rustc_diagnostic_item = "Enumerate" )] |
19 | pub struct Enumerate<I> { |
20 | iter: I, |
21 | count: usize, |
22 | } |
23 | impl<I> Enumerate<I> { |
24 | pub(in crate::iter) fn new(iter: I) -> Enumerate<I> { |
25 | Enumerate { iter, count: 0 } |
26 | } |
27 | } |
28 | |
29 | #[stable (feature = "rust1" , since = "1.0.0" )] |
30 | impl<I> Iterator for Enumerate<I> |
31 | where |
32 | I: Iterator, |
33 | { |
34 | type Item = (usize, <I as Iterator>::Item); |
35 | |
36 | /// # Overflow Behavior |
37 | /// |
38 | /// The method does no guarding against overflows, so enumerating more than |
39 | /// `usize::MAX` elements either produces the wrong result or panics. If |
40 | /// debug assertions are enabled, a panic is guaranteed. |
41 | /// |
42 | /// # Panics |
43 | /// |
44 | /// Might panic if the index of the element overflows a `usize`. |
45 | #[inline ] |
46 | #[rustc_inherit_overflow_checks ] |
47 | fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> { |
48 | let a = self.iter.next()?; |
49 | let i = self.count; |
50 | self.count += 1; |
51 | Some((i, a)) |
52 | } |
53 | |
54 | #[inline ] |
55 | fn size_hint(&self) -> (usize, Option<usize>) { |
56 | self.iter.size_hint() |
57 | } |
58 | |
59 | #[inline ] |
60 | #[rustc_inherit_overflow_checks ] |
61 | fn nth(&mut self, n: usize) -> Option<(usize, I::Item)> { |
62 | let a = self.iter.nth(n)?; |
63 | let i = self.count + n; |
64 | self.count = i + 1; |
65 | Some((i, a)) |
66 | } |
67 | |
68 | #[inline ] |
69 | fn count(self) -> usize { |
70 | self.iter.count() |
71 | } |
72 | |
73 | #[inline ] |
74 | fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R |
75 | where |
76 | Self: Sized, |
77 | Fold: FnMut(Acc, Self::Item) -> R, |
78 | R: Try<Output = Acc>, |
79 | { |
80 | #[inline ] |
81 | fn enumerate<'a, T, Acc, R>( |
82 | count: &'a mut usize, |
83 | mut fold: impl FnMut(Acc, (usize, T)) -> R + 'a, |
84 | ) -> impl FnMut(Acc, T) -> R + 'a { |
85 | #[rustc_inherit_overflow_checks ] |
86 | move |acc, item| { |
87 | let acc = fold(acc, (*count, item)); |
88 | *count += 1; |
89 | acc |
90 | } |
91 | } |
92 | |
93 | self.iter.try_fold(init, enumerate(&mut self.count, 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 | #[inline ] |
102 | fn enumerate<T, Acc>( |
103 | mut count: usize, |
104 | mut fold: impl FnMut(Acc, (usize, T)) -> Acc, |
105 | ) -> impl FnMut(Acc, T) -> Acc { |
106 | #[rustc_inherit_overflow_checks ] |
107 | move |acc, item| { |
108 | let acc = fold(acc, (count, item)); |
109 | count += 1; |
110 | acc |
111 | } |
112 | } |
113 | |
114 | self.iter.fold(init, enumerate(self.count, fold)) |
115 | } |
116 | |
117 | #[inline ] |
118 | #[rustc_inherit_overflow_checks ] |
119 | fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> { |
120 | let remaining = self.iter.advance_by(n); |
121 | let advanced = match remaining { |
122 | Ok(()) => n, |
123 | Err(rem) => n - rem.get(), |
124 | }; |
125 | self.count += advanced; |
126 | remaining |
127 | } |
128 | |
129 | #[rustc_inherit_overflow_checks ] |
130 | #[inline ] |
131 | unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> <Self as Iterator>::Item |
132 | where |
133 | Self: TrustedRandomAccessNoCoerce, |
134 | { |
135 | // SAFETY: the caller must uphold the contract for |
136 | // `Iterator::__iterator_get_unchecked`. |
137 | let value = unsafe { try_get_unchecked(&mut self.iter, idx) }; |
138 | (self.count + idx, value) |
139 | } |
140 | } |
141 | |
142 | #[stable (feature = "rust1" , since = "1.0.0" )] |
143 | impl<I> DoubleEndedIterator for Enumerate<I> |
144 | where |
145 | I: ExactSizeIterator + DoubleEndedIterator, |
146 | { |
147 | #[inline ] |
148 | fn next_back(&mut self) -> Option<(usize, <I as Iterator>::Item)> { |
149 | let a = self.iter.next_back()?; |
150 | let len = self.iter.len(); |
151 | // Can safely add, `ExactSizeIterator` promises that the number of |
152 | // elements fits into a `usize`. |
153 | Some((self.count + len, a)) |
154 | } |
155 | |
156 | #[inline ] |
157 | fn nth_back(&mut self, n: usize) -> Option<(usize, <I as Iterator>::Item)> { |
158 | let a = self.iter.nth_back(n)?; |
159 | let len = self.iter.len(); |
160 | // Can safely add, `ExactSizeIterator` promises that the number of |
161 | // elements fits into a `usize`. |
162 | Some((self.count + len, a)) |
163 | } |
164 | |
165 | #[inline ] |
166 | fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R |
167 | where |
168 | Self: Sized, |
169 | Fold: FnMut(Acc, Self::Item) -> R, |
170 | R: Try<Output = Acc>, |
171 | { |
172 | // Can safely add and subtract the count, as `ExactSizeIterator` promises |
173 | // that the number of elements fits into a `usize`. |
174 | fn enumerate<T, Acc, R>( |
175 | mut count: usize, |
176 | mut fold: impl FnMut(Acc, (usize, T)) -> R, |
177 | ) -> impl FnMut(Acc, T) -> R { |
178 | move |acc, item| { |
179 | count -= 1; |
180 | fold(acc, (count, item)) |
181 | } |
182 | } |
183 | |
184 | let count = self.count + self.iter.len(); |
185 | self.iter.try_rfold(init, enumerate(count, fold)) |
186 | } |
187 | |
188 | #[inline ] |
189 | fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc |
190 | where |
191 | Fold: FnMut(Acc, Self::Item) -> Acc, |
192 | { |
193 | // Can safely add and subtract the count, as `ExactSizeIterator` promises |
194 | // that the number of elements fits into a `usize`. |
195 | fn enumerate<T, Acc>( |
196 | mut count: usize, |
197 | mut fold: impl FnMut(Acc, (usize, T)) -> Acc, |
198 | ) -> impl FnMut(Acc, T) -> Acc { |
199 | move |acc, item| { |
200 | count -= 1; |
201 | fold(acc, (count, item)) |
202 | } |
203 | } |
204 | |
205 | let count = self.count + self.iter.len(); |
206 | self.iter.rfold(init, enumerate(count, fold)) |
207 | } |
208 | |
209 | #[inline ] |
210 | fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> { |
211 | // we do not need to update the count since that only tallies the number of items |
212 | // consumed from the front. consuming items from the back can never reduce that. |
213 | self.iter.advance_back_by(n) |
214 | } |
215 | } |
216 | |
217 | #[stable (feature = "rust1" , since = "1.0.0" )] |
218 | impl<I> ExactSizeIterator for Enumerate<I> |
219 | where |
220 | I: ExactSizeIterator, |
221 | { |
222 | fn len(&self) -> usize { |
223 | self.iter.len() |
224 | } |
225 | |
226 | fn is_empty(&self) -> bool { |
227 | self.iter.is_empty() |
228 | } |
229 | } |
230 | |
231 | #[doc (hidden)] |
232 | #[unstable (feature = "trusted_random_access" , issue = "none" )] |
233 | unsafe impl<I> TrustedRandomAccess for Enumerate<I> where I: TrustedRandomAccess {} |
234 | |
235 | #[doc (hidden)] |
236 | #[unstable (feature = "trusted_random_access" , issue = "none" )] |
237 | unsafe impl<I> TrustedRandomAccessNoCoerce for Enumerate<I> |
238 | where |
239 | I: TrustedRandomAccessNoCoerce, |
240 | { |
241 | const MAY_HAVE_SIDE_EFFECT: bool = I::MAY_HAVE_SIDE_EFFECT; |
242 | } |
243 | |
244 | #[stable (feature = "fused" , since = "1.26.0" )] |
245 | impl<I> FusedIterator for Enumerate<I> where I: FusedIterator {} |
246 | |
247 | #[unstable (issue = "none" , feature = "trusted_fused" )] |
248 | unsafe impl<I: TrustedFused> TrustedFused for Enumerate<I> {} |
249 | |
250 | #[unstable (feature = "trusted_len" , issue = "37572" )] |
251 | unsafe impl<I> TrustedLen for Enumerate<I> where I: TrustedLen {} |
252 | |
253 | #[unstable (issue = "none" , feature = "inplace_iteration" )] |
254 | unsafe impl<I> SourceIter for Enumerate<I> |
255 | where |
256 | I: SourceIter, |
257 | { |
258 | type Source = I::Source; |
259 | |
260 | #[inline ] |
261 | unsafe fn as_inner(&mut self) -> &mut I::Source { |
262 | // SAFETY: unsafe function forwarding to unsafe function with the same requirements |
263 | unsafe { SourceIter::as_inner(&mut self.iter) } |
264 | } |
265 | } |
266 | |
267 | #[unstable (issue = "none" , feature = "inplace_iteration" )] |
268 | unsafe impl<I: InPlaceIterable> InPlaceIterable for Enumerate<I> { |
269 | const EXPAND_BY: Option<NonZero<usize>> = I::EXPAND_BY; |
270 | const MERGE_BY: Option<NonZero<usize>> = I::MERGE_BY; |
271 | } |
272 | |
273 | #[stable (feature = "default_iters" , since = "1.70.0" )] |
274 | impl<I: Default> Default for Enumerate<I> { |
275 | /// Creates an `Enumerate` iterator from the default value of `I` |
276 | /// ``` |
277 | /// # use core::slice; |
278 | /// # use std::iter::Enumerate; |
279 | /// let iter: Enumerate<slice::Iter<'_, u8>> = Default::default(); |
280 | /// assert_eq!(iter.len(), 0); |
281 | /// ``` |
282 | fn default() -> Self { |
283 | Enumerate::new(iter:Default::default()) |
284 | } |
285 | } |
286 | |