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Commit | Line | Data |
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e1599b0c | 1 | use crate::cmp::{self, Ordering}; |
a2a8927a | 2 | use crate::ops::{ChangeOutputType, ControlFlow, FromResidual, Residual, Try}; |
a7813a04 | 3 | |
5099ac24 | 4 | use super::super::try_process; |
5e7ed085 | 5 | use super::super::ByRefSized; |
94222f64 | 6 | use super::super::TrustedRandomAccessNoCoerce; |
dfeec247 XL |
7 | use super::super::{Chain, Cloned, Copied, Cycle, Enumerate, Filter, FilterMap, Fuse}; |
8 | use super::super::{FlatMap, Flatten}; | |
5869c6ff | 9 | use super::super::{FromIterator, Intersperse, IntersperseWith, Product, Sum, Zip}; |
74b04a01 XL |
10 | use super::super::{ |
11 | Inspect, Map, MapWhile, Peekable, Rev, Scan, Skip, SkipWhile, StepBy, Take, TakeWhile, | |
12 | }; | |
a7813a04 | 13 | |
dfeec247 | 14 | fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {} |
a7813a04 XL |
15 | |
16 | /// An interface for dealing with iterators. | |
17 | /// | |
18 | /// This is the main iterator trait. For more about the concept of iterators | |
19 | /// generally, please see the [module-level documentation]. In particular, you | |
20 | /// may want to know how to [implement `Iterator`][impl]. | |
21 | /// | |
1b1a35ee XL |
22 | /// [module-level documentation]: crate::iter |
23 | /// [impl]: crate::iter#implementing-iterator | |
a7813a04 | 24 | #[stable(feature = "rust1", since = "1.0.0")] |
2c00a5a8 | 25 | #[rustc_on_unimplemented( |
0bf4aa26 | 26 | on( |
dfeec247 XL |
27 | _Self = "std::ops::RangeTo<Idx>", |
28 | label = "if you meant to iterate until a value, add a starting value", | |
29 | note = "`..end` is a `RangeTo`, which cannot be iterated on; you might have meant to have a \ | |
0bf4aa26 XL |
30 | bounded `Range`: `0..end`" |
31 | ), | |
32 | on( | |
dfeec247 XL |
33 | _Self = "std::ops::RangeToInclusive<Idx>", |
34 | label = "if you meant to iterate until a value (including it), add a starting value", | |
35 | note = "`..=end` is a `RangeToInclusive`, which cannot be iterated on; you might have meant \ | |
0bf4aa26 XL |
36 | to have a bounded `RangeInclusive`: `0..=end`" |
37 | ), | |
5e7ed085 FG |
38 | on( |
39 | _Self = "[]", | |
40 | label = "`{Self}` is not an iterator; try calling `.into_iter()` or `.iter()`" | |
41 | ), | |
42 | on(_Self = "&[]", label = "`{Self}` is not an iterator; try calling `.iter()`"), | |
923072b8 FG |
43 | on( |
44 | _Self = "std::vec::Vec<T, A>", | |
45 | label = "`{Self}` is not an iterator; try calling `.into_iter()` or `.iter()`" | |
46 | ), | |
2c00a5a8 | 47 | on( |
dfeec247 XL |
48 | _Self = "&str", |
49 | label = "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`" | |
2c00a5a8 | 50 | ), |
0bf4aa26 | 51 | on( |
dfeec247 XL |
52 | _Self = "std::string::String", |
53 | label = "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`" | |
0bf4aa26 | 54 | ), |
0bf4aa26 | 55 | on( |
dfeec247 XL |
56 | _Self = "{integral}", |
57 | note = "if you want to iterate between `start` until a value `end`, use the exclusive range \ | |
0bf4aa26 XL |
58 | syntax `start..end` or the inclusive range syntax `start..=end`" |
59 | ), | |
dfeec247 XL |
60 | label = "`{Self}` is not an iterator", |
61 | message = "`{Self}` is not an iterator" | |
2c00a5a8 | 62 | )] |
17df50a5 | 63 | #[doc(notable_trait)] |
6a06907d | 64 | #[rustc_diagnostic_item = "Iterator"] |
0731742a | 65 | #[must_use = "iterators are lazy and do nothing unless consumed"] |
a7813a04 XL |
66 | pub trait Iterator { |
67 | /// The type of the elements being iterated over. | |
68 | #[stable(feature = "rust1", since = "1.0.0")] | |
69 | type Item; | |
70 | ||
71 | /// Advances the iterator and returns the next value. | |
72 | /// | |
476ff2be | 73 | /// Returns [`None`] when iteration is finished. Individual iterator |
a7813a04 | 74 | /// implementations may choose to resume iteration, and so calling `next()` |
476ff2be | 75 | /// again may or may not eventually start returning [`Some(Item)`] again at some |
a7813a04 XL |
76 | /// point. |
77 | /// | |
3dfed10e | 78 | /// [`Some(Item)`]: Some |
476ff2be | 79 | /// |
a7813a04 XL |
80 | /// # Examples |
81 | /// | |
82 | /// Basic usage: | |
83 | /// | |
84 | /// ``` | |
85 | /// let a = [1, 2, 3]; | |
86 | /// | |
87 | /// let mut iter = a.iter(); | |
88 | /// | |
89 | /// // A call to next() returns the next value... | |
90 | /// assert_eq!(Some(&1), iter.next()); | |
91 | /// assert_eq!(Some(&2), iter.next()); | |
92 | /// assert_eq!(Some(&3), iter.next()); | |
93 | /// | |
94 | /// // ... and then None once it's over. | |
95 | /// assert_eq!(None, iter.next()); | |
96 | /// | |
9fa01778 | 97 | /// // More calls may or may not return `None`. Here, they always will. |
a7813a04 XL |
98 | /// assert_eq!(None, iter.next()); |
99 | /// assert_eq!(None, iter.next()); | |
100 | /// ``` | |
1b1a35ee | 101 | #[lang = "next"] |
a7813a04 XL |
102 | #[stable(feature = "rust1", since = "1.0.0")] |
103 | fn next(&mut self) -> Option<Self::Item>; | |
104 | ||
105 | /// Returns the bounds on the remaining length of the iterator. | |
106 | /// | |
107 | /// Specifically, `size_hint()` returns a tuple where the first element | |
108 | /// is the lower bound, and the second element is the upper bound. | |
109 | /// | |
c295e0f8 | 110 | /// The second half of the tuple that is returned is an <code>[Option]<[usize]></code>. |
476ff2be SL |
111 | /// A [`None`] here means that either there is no known upper bound, or the |
112 | /// upper bound is larger than [`usize`]. | |
a7813a04 XL |
113 | /// |
114 | /// # Implementation notes | |
115 | /// | |
116 | /// It is not enforced that an iterator implementation yields the declared | |
117 | /// number of elements. A buggy iterator may yield less than the lower bound | |
118 | /// or more than the upper bound of elements. | |
119 | /// | |
120 | /// `size_hint()` is primarily intended to be used for optimizations such as | |
121 | /// reserving space for the elements of the iterator, but must not be | |
0731742a | 122 | /// trusted to e.g., omit bounds checks in unsafe code. An incorrect |
a7813a04 XL |
123 | /// implementation of `size_hint()` should not lead to memory safety |
124 | /// violations. | |
125 | /// | |
126 | /// That said, the implementation should provide a correct estimation, | |
127 | /// because otherwise it would be a violation of the trait's protocol. | |
128 | /// | |
c295e0f8 | 129 | /// The default implementation returns <code>(0, [None])</code> which is correct for any |
a7813a04 XL |
130 | /// iterator. |
131 | /// | |
132 | /// # Examples | |
133 | /// | |
134 | /// Basic usage: | |
135 | /// | |
136 | /// ``` | |
137 | /// let a = [1, 2, 3]; | |
138 | /// let iter = a.iter(); | |
139 | /// | |
140 | /// assert_eq!((3, Some(3)), iter.size_hint()); | |
141 | /// ``` | |
142 | /// | |
143 | /// A more complex example: | |
144 | /// | |
145 | /// ``` | |
17df50a5 | 146 | /// // The even numbers in the range of zero to nine. |
a7813a04 XL |
147 | /// let iter = (0..10).filter(|x| x % 2 == 0); |
148 | /// | |
149 | /// // We might iterate from zero to ten times. Knowing that it's five | |
150 | /// // exactly wouldn't be possible without executing filter(). | |
151 | /// assert_eq!((0, Some(10)), iter.size_hint()); | |
152 | /// | |
7cac9316 | 153 | /// // Let's add five more numbers with chain() |
a7813a04 XL |
154 | /// let iter = (0..10).filter(|x| x % 2 == 0).chain(15..20); |
155 | /// | |
156 | /// // now both bounds are increased by five | |
157 | /// assert_eq!((5, Some(15)), iter.size_hint()); | |
158 | /// ``` | |
159 | /// | |
160 | /// Returning `None` for an upper bound: | |
161 | /// | |
162 | /// ``` | |
163 | /// // an infinite iterator has no upper bound | |
7cac9316 | 164 | /// // and the maximum possible lower bound |
a7813a04 XL |
165 | /// let iter = 0..; |
166 | /// | |
ba9703b0 | 167 | /// assert_eq!((usize::MAX, None), iter.size_hint()); |
a7813a04 XL |
168 | /// ``` |
169 | #[inline] | |
170 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
171 | fn size_hint(&self) -> (usize, Option<usize>) { |
172 | (0, None) | |
173 | } | |
a7813a04 XL |
174 | |
175 | /// Consumes the iterator, counting the number of iterations and returning it. | |
176 | /// | |
60c5eb7d XL |
177 | /// This method will call [`next`] repeatedly until [`None`] is encountered, |
178 | /// returning the number of times it saw [`Some`]. Note that [`next`] has to be | |
179 | /// called at least once even if the iterator does not have any elements. | |
a7813a04 | 180 | /// |
1b1a35ee | 181 | /// [`next`]: Iterator::next |
a7813a04 XL |
182 | /// |
183 | /// # Overflow Behavior | |
184 | /// | |
185 | /// The method does no guarding against overflows, so counting elements of | |
476ff2be | 186 | /// an iterator with more than [`usize::MAX`] elements either produces the |
a7813a04 XL |
187 | /// wrong result or panics. If debug assertions are enabled, a panic is |
188 | /// guaranteed. | |
189 | /// | |
190 | /// # Panics | |
191 | /// | |
476ff2be | 192 | /// This function might panic if the iterator has more than [`usize::MAX`] |
a7813a04 XL |
193 | /// elements. |
194 | /// | |
195 | /// # Examples | |
196 | /// | |
197 | /// Basic usage: | |
198 | /// | |
199 | /// ``` | |
200 | /// let a = [1, 2, 3]; | |
201 | /// assert_eq!(a.iter().count(), 3); | |
202 | /// | |
203 | /// let a = [1, 2, 3, 4, 5]; | |
204 | /// assert_eq!(a.iter().count(), 5); | |
205 | /// ``` | |
206 | #[inline] | |
207 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
208 | fn count(self) -> usize |
209 | where | |
210 | Self: Sized, | |
211 | { | |
6a06907d XL |
212 | self.fold( |
213 | 0, | |
214 | #[rustc_inherit_overflow_checks] | |
215 | |count, _| count + 1, | |
216 | ) | |
a7813a04 XL |
217 | } |
218 | ||
219 | /// Consumes the iterator, returning the last element. | |
220 | /// | |
476ff2be SL |
221 | /// This method will evaluate the iterator until it returns [`None`]. While |
222 | /// doing so, it keeps track of the current element. After [`None`] is | |
a7813a04 XL |
223 | /// returned, `last()` will then return the last element it saw. |
224 | /// | |
225 | /// # Examples | |
226 | /// | |
227 | /// Basic usage: | |
228 | /// | |
229 | /// ``` | |
230 | /// let a = [1, 2, 3]; | |
231 | /// assert_eq!(a.iter().last(), Some(&3)); | |
232 | /// | |
233 | /// let a = [1, 2, 3, 4, 5]; | |
234 | /// assert_eq!(a.iter().last(), Some(&5)); | |
235 | /// ``` | |
236 | #[inline] | |
237 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
238 | fn last(self) -> Option<Self::Item> |
239 | where | |
240 | Self: Sized, | |
241 | { | |
e1599b0c XL |
242 | #[inline] |
243 | fn some<T>(_: Option<T>, x: T) -> Option<T> { | |
244 | Some(x) | |
245 | } | |
246 | ||
247 | self.fold(None, some) | |
a7813a04 XL |
248 | } |
249 | ||
1b1a35ee XL |
250 | /// Advances the iterator by `n` elements. |
251 | /// | |
252 | /// This method will eagerly skip `n` elements by calling [`next`] up to `n` | |
253 | /// times until [`None`] is encountered. | |
254 | /// | |
29967ef6 XL |
255 | /// `advance_by(n)` will return [`Ok(())`][Ok] if the iterator successfully advances by |
256 | /// `n` elements, or [`Err(k)`][Err] if [`None`] is encountered, where `k` is the number | |
1b1a35ee XL |
257 | /// of elements the iterator is advanced by before running out of elements (i.e. the |
258 | /// length of the iterator). Note that `k` is always less than `n`. | |
259 | /// | |
c295e0f8 XL |
260 | /// Calling `advance_by(0)` can do meaningful work, for example [`Flatten`] |
261 | /// can advance its outer iterator until it finds an inner iterator that is not empty, which | |
262 | /// then often allows it to return a more accurate `size_hint()` than in its initial state. | |
1b1a35ee | 263 | /// |
c295e0f8 | 264 | /// [`Flatten`]: crate::iter::Flatten |
1b1a35ee XL |
265 | /// [`next`]: Iterator::next |
266 | /// | |
267 | /// # Examples | |
268 | /// | |
269 | /// Basic usage: | |
270 | /// | |
271 | /// ``` | |
272 | /// #![feature(iter_advance_by)] | |
273 | /// | |
274 | /// let a = [1, 2, 3, 4]; | |
275 | /// let mut iter = a.iter(); | |
276 | /// | |
277 | /// assert_eq!(iter.advance_by(2), Ok(())); | |
278 | /// assert_eq!(iter.next(), Some(&3)); | |
279 | /// assert_eq!(iter.advance_by(0), Ok(())); | |
280 | /// assert_eq!(iter.advance_by(100), Err(1)); // only `&4` was skipped | |
281 | /// ``` | |
282 | #[inline] | |
283 | #[unstable(feature = "iter_advance_by", reason = "recently added", issue = "77404")] | |
284 | fn advance_by(&mut self, n: usize) -> Result<(), usize> { | |
285 | for i in 0..n { | |
286 | self.next().ok_or(i)?; | |
287 | } | |
288 | Ok(()) | |
289 | } | |
290 | ||
c30ab7b3 | 291 | /// Returns the `n`th element of the iterator. |
a7813a04 | 292 | /// |
a7813a04 XL |
293 | /// Like most indexing operations, the count starts from zero, so `nth(0)` |
294 | /// returns the first value, `nth(1)` the second, and so on. | |
295 | /// | |
8bb4bdeb XL |
296 | /// Note that all preceding elements, as well as the returned element, will be |
297 | /// consumed from the iterator. That means that the preceding elements will be | |
298 | /// discarded, and also that calling `nth(0)` multiple times on the same iterator | |
299 | /// will return different elements. | |
300 | /// | |
476ff2be | 301 | /// `nth()` will return [`None`] if `n` is greater than or equal to the length of the |
a7813a04 XL |
302 | /// iterator. |
303 | /// | |
304 | /// # Examples | |
305 | /// | |
306 | /// Basic usage: | |
307 | /// | |
308 | /// ``` | |
309 | /// let a = [1, 2, 3]; | |
310 | /// assert_eq!(a.iter().nth(1), Some(&2)); | |
311 | /// ``` | |
312 | /// | |
313 | /// Calling `nth()` multiple times doesn't rewind the iterator: | |
314 | /// | |
315 | /// ``` | |
316 | /// let a = [1, 2, 3]; | |
317 | /// | |
318 | /// let mut iter = a.iter(); | |
319 | /// | |
320 | /// assert_eq!(iter.nth(1), Some(&2)); | |
321 | /// assert_eq!(iter.nth(1), None); | |
322 | /// ``` | |
323 | /// | |
324 | /// Returning `None` if there are less than `n + 1` elements: | |
325 | /// | |
326 | /// ``` | |
327 | /// let a = [1, 2, 3]; | |
328 | /// assert_eq!(a.iter().nth(10), None); | |
329 | /// ``` | |
330 | #[inline] | |
331 | #[stable(feature = "rust1", since = "1.0.0")] | |
1b1a35ee XL |
332 | fn nth(&mut self, n: usize) -> Option<Self::Item> { |
333 | self.advance_by(n).ok()?; | |
334 | self.next() | |
a7813a04 XL |
335 | } |
336 | ||
7cac9316 XL |
337 | /// Creates an iterator starting at the same point, but stepping by |
338 | /// the given amount at each iteration. | |
339 | /// | |
94b46f34 | 340 | /// Note 1: The first element of the iterator will always be returned, |
7cac9316 XL |
341 | /// regardless of the step given. |
342 | /// | |
94b46f34 | 343 | /// Note 2: The time at which ignored elements are pulled is not fixed. |
136023e0 XL |
344 | /// `StepBy` behaves like the sequence `self.next()`, `self.nth(step-1)`, |
345 | /// `self.nth(step-1)`, …, but is also free to behave like the sequence | |
346 | /// `advance_n_and_return_first(&mut self, step)`, | |
347 | /// `advance_n_and_return_first(&mut self, step)`, … | |
94b46f34 XL |
348 | /// Which way is used may change for some iterators for performance reasons. |
349 | /// The second way will advance the iterator earlier and may consume more items. | |
350 | /// | |
351 | /// `advance_n_and_return_first` is the equivalent of: | |
352 | /// ``` | |
136023e0 | 353 | /// fn advance_n_and_return_first<I>(iter: &mut I, n: usize) -> Option<I::Item> |
94b46f34 XL |
354 | /// where |
355 | /// I: Iterator, | |
356 | /// { | |
357 | /// let next = iter.next(); | |
136023e0 XL |
358 | /// if n > 1 { |
359 | /// iter.nth(n - 2); | |
94b46f34 XL |
360 | /// } |
361 | /// next | |
362 | /// } | |
363 | /// ``` | |
364 | /// | |
7cac9316 XL |
365 | /// # Panics |
366 | /// | |
367 | /// The method will panic if the given step is `0`. | |
368 | /// | |
369 | /// # Examples | |
370 | /// | |
371 | /// Basic usage: | |
372 | /// | |
373 | /// ``` | |
7cac9316 | 374 | /// let a = [0, 1, 2, 3, 4, 5]; |
48663c56 | 375 | /// let mut iter = a.iter().step_by(2); |
7cac9316 XL |
376 | /// |
377 | /// assert_eq!(iter.next(), Some(&0)); | |
378 | /// assert_eq!(iter.next(), Some(&2)); | |
379 | /// assert_eq!(iter.next(), Some(&4)); | |
380 | /// assert_eq!(iter.next(), None); | |
381 | /// ``` | |
382 | #[inline] | |
94b46f34 | 383 | #[stable(feature = "iterator_step_by", since = "1.28.0")] |
dfeec247 XL |
384 | fn step_by(self, step: usize) -> StepBy<Self> |
385 | where | |
386 | Self: Sized, | |
387 | { | |
9fa01778 | 388 | StepBy::new(self, step) |
7cac9316 XL |
389 | } |
390 | ||
a7813a04 XL |
391 | /// Takes two iterators and creates a new iterator over both in sequence. |
392 | /// | |
393 | /// `chain()` will return a new iterator which will first iterate over | |
394 | /// values from the first iterator and then over values from the second | |
395 | /// iterator. | |
396 | /// | |
397 | /// In other words, it links two iterators together, in a chain. 🔗 | |
398 | /// | |
e74abb32 XL |
399 | /// [`once`] is commonly used to adapt a single value into a chain of |
400 | /// other kinds of iteration. | |
401 | /// | |
a7813a04 XL |
402 | /// # Examples |
403 | /// | |
404 | /// Basic usage: | |
405 | /// | |
406 | /// ``` | |
407 | /// let a1 = [1, 2, 3]; | |
408 | /// let a2 = [4, 5, 6]; | |
409 | /// | |
410 | /// let mut iter = a1.iter().chain(a2.iter()); | |
411 | /// | |
412 | /// assert_eq!(iter.next(), Some(&1)); | |
413 | /// assert_eq!(iter.next(), Some(&2)); | |
414 | /// assert_eq!(iter.next(), Some(&3)); | |
415 | /// assert_eq!(iter.next(), Some(&4)); | |
416 | /// assert_eq!(iter.next(), Some(&5)); | |
417 | /// assert_eq!(iter.next(), Some(&6)); | |
418 | /// assert_eq!(iter.next(), None); | |
419 | /// ``` | |
420 | /// | |
421 | /// Since the argument to `chain()` uses [`IntoIterator`], we can pass | |
422 | /// anything that can be converted into an [`Iterator`], not just an | |
423 | /// [`Iterator`] itself. For example, slices (`&[T]`) implement | |
424 | /// [`IntoIterator`], and so can be passed to `chain()` directly: | |
425 | /// | |
a7813a04 XL |
426 | /// ``` |
427 | /// let s1 = &[1, 2, 3]; | |
428 | /// let s2 = &[4, 5, 6]; | |
429 | /// | |
430 | /// let mut iter = s1.iter().chain(s2); | |
431 | /// | |
432 | /// assert_eq!(iter.next(), Some(&1)); | |
433 | /// assert_eq!(iter.next(), Some(&2)); | |
434 | /// assert_eq!(iter.next(), Some(&3)); | |
435 | /// assert_eq!(iter.next(), Some(&4)); | |
436 | /// assert_eq!(iter.next(), Some(&5)); | |
437 | /// assert_eq!(iter.next(), Some(&6)); | |
438 | /// assert_eq!(iter.next(), None); | |
439 | /// ``` | |
e74abb32 XL |
440 | /// |
441 | /// If you work with Windows API, you may wish to convert [`OsStr`] to `Vec<u16>`: | |
442 | /// | |
443 | /// ``` | |
444 | /// #[cfg(windows)] | |
445 | /// fn os_str_to_utf16(s: &std::ffi::OsStr) -> Vec<u16> { | |
446 | /// use std::os::windows::ffi::OsStrExt; | |
447 | /// s.encode_wide().chain(std::iter::once(0)).collect() | |
448 | /// } | |
449 | /// ``` | |
450 | /// | |
1b1a35ee | 451 | /// [`once`]: crate::iter::once |
e74abb32 | 452 | /// [`OsStr`]: ../../std/ffi/struct.OsStr.html |
a7813a04 XL |
453 | #[inline] |
454 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
455 | fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> |
456 | where | |
457 | Self: Sized, | |
458 | U: IntoIterator<Item = Self::Item>, | |
a7813a04 | 459 | { |
9fa01778 | 460 | Chain::new(self, other.into_iter()) |
a7813a04 XL |
461 | } |
462 | ||
463 | /// 'Zips up' two iterators into a single iterator of pairs. | |
464 | /// | |
465 | /// `zip()` returns a new iterator that will iterate over two other | |
466 | /// iterators, returning a tuple where the first element comes from the | |
467 | /// first iterator, and the second element comes from the second iterator. | |
468 | /// | |
469 | /// In other words, it zips two iterators together, into a single one. | |
470 | /// | |
8faf50e0 | 471 | /// If either iterator returns [`None`], [`next`] from the zipped iterator |
a2a8927a XL |
472 | /// will return [`None`]. |
473 | /// If the zipped iterator has no more elements to return then each further attempt to advance | |
474 | /// it will first try to advance the first iterator at most one time and if it still yielded an item | |
475 | /// try to advance the second iterator at most one time. | |
a7813a04 | 476 | /// |
04454e1e FG |
477 | /// To 'undo' the result of zipping up two iterators, see [`unzip`]. |
478 | /// | |
479 | /// [`unzip`]: Iterator::unzip | |
480 | /// | |
a7813a04 XL |
481 | /// # Examples |
482 | /// | |
483 | /// Basic usage: | |
484 | /// | |
485 | /// ``` | |
486 | /// let a1 = [1, 2, 3]; | |
487 | /// let a2 = [4, 5, 6]; | |
488 | /// | |
489 | /// let mut iter = a1.iter().zip(a2.iter()); | |
490 | /// | |
491 | /// assert_eq!(iter.next(), Some((&1, &4))); | |
492 | /// assert_eq!(iter.next(), Some((&2, &5))); | |
493 | /// assert_eq!(iter.next(), Some((&3, &6))); | |
494 | /// assert_eq!(iter.next(), None); | |
495 | /// ``` | |
496 | /// | |
497 | /// Since the argument to `zip()` uses [`IntoIterator`], we can pass | |
498 | /// anything that can be converted into an [`Iterator`], not just an | |
499 | /// [`Iterator`] itself. For example, slices (`&[T]`) implement | |
500 | /// [`IntoIterator`], and so can be passed to `zip()` directly: | |
501 | /// | |
a7813a04 XL |
502 | /// ``` |
503 | /// let s1 = &[1, 2, 3]; | |
504 | /// let s2 = &[4, 5, 6]; | |
505 | /// | |
506 | /// let mut iter = s1.iter().zip(s2); | |
507 | /// | |
508 | /// assert_eq!(iter.next(), Some((&1, &4))); | |
509 | /// assert_eq!(iter.next(), Some((&2, &5))); | |
510 | /// assert_eq!(iter.next(), Some((&3, &6))); | |
511 | /// assert_eq!(iter.next(), None); | |
512 | /// ``` | |
513 | /// | |
514 | /// `zip()` is often used to zip an infinite iterator to a finite one. | |
476ff2be | 515 | /// This works because the finite iterator will eventually return [`None`], |
cc61c64b | 516 | /// ending the zipper. Zipping with `(0..)` can look a lot like [`enumerate`]: |
a7813a04 XL |
517 | /// |
518 | /// ``` | |
519 | /// let enumerate: Vec<_> = "foo".chars().enumerate().collect(); | |
520 | /// | |
521 | /// let zipper: Vec<_> = (0..).zip("foo".chars()).collect(); | |
522 | /// | |
523 | /// assert_eq!((0, 'f'), enumerate[0]); | |
524 | /// assert_eq!((0, 'f'), zipper[0]); | |
525 | /// | |
526 | /// assert_eq!((1, 'o'), enumerate[1]); | |
527 | /// assert_eq!((1, 'o'), zipper[1]); | |
528 | /// | |
529 | /// assert_eq!((2, 'o'), enumerate[2]); | |
530 | /// assert_eq!((2, 'o'), zipper[2]); | |
531 | /// ``` | |
532 | /// | |
5099ac24 FG |
533 | /// If both iterators have roughly equivalent syntax, it may be more readable to use [`zip`]: |
534 | /// | |
535 | /// ``` | |
536 | /// use std::iter::zip; | |
537 | /// | |
538 | /// let a = [1, 2, 3]; | |
539 | /// let b = [2, 3, 4]; | |
540 | /// | |
541 | /// let mut zipped = zip( | |
542 | /// a.into_iter().map(|x| x * 2).skip(1), | |
543 | /// b.into_iter().map(|x| x * 2).skip(1), | |
544 | /// ); | |
545 | /// | |
546 | /// assert_eq!(zipped.next(), Some((4, 6))); | |
547 | /// assert_eq!(zipped.next(), Some((6, 8))); | |
548 | /// assert_eq!(zipped.next(), None); | |
549 | /// ``` | |
550 | /// | |
551 | /// compared to: | |
552 | /// | |
553 | /// ``` | |
554 | /// # let a = [1, 2, 3]; | |
555 | /// # let b = [2, 3, 4]; | |
556 | /// # | |
557 | /// let mut zipped = a | |
558 | /// .into_iter() | |
559 | /// .map(|x| x * 2) | |
560 | /// .skip(1) | |
561 | /// .zip(b.into_iter().map(|x| x * 2).skip(1)); | |
562 | /// # | |
563 | /// # assert_eq!(zipped.next(), Some((4, 6))); | |
564 | /// # assert_eq!(zipped.next(), Some((6, 8))); | |
565 | /// # assert_eq!(zipped.next(), None); | |
566 | /// ``` | |
567 | /// | |
1b1a35ee XL |
568 | /// [`enumerate`]: Iterator::enumerate |
569 | /// [`next`]: Iterator::next | |
5099ac24 | 570 | /// [`zip`]: crate::iter::zip |
a7813a04 XL |
571 | #[inline] |
572 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
573 | fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> |
574 | where | |
575 | Self: Sized, | |
576 | U: IntoIterator, | |
a7813a04 | 577 | { |
3157f602 | 578 | Zip::new(self, other.into_iter()) |
a7813a04 XL |
579 | } |
580 | ||
5869c6ff XL |
581 | /// Creates a new iterator which places a copy of `separator` between adjacent |
582 | /// items of the original iterator. | |
583 | /// | |
584 | /// In case `separator` does not implement [`Clone`] or needs to be | |
585 | /// computed every time, use [`intersperse_with`]. | |
586 | /// | |
587 | /// # Examples | |
588 | /// | |
589 | /// Basic usage: | |
590 | /// | |
591 | /// ``` | |
dc3f5686 XL |
592 | /// #![feature(iter_intersperse)] |
593 | /// | |
5869c6ff XL |
594 | /// let mut a = [0, 1, 2].iter().intersperse(&100); |
595 | /// assert_eq!(a.next(), Some(&0)); // The first element from `a`. | |
596 | /// assert_eq!(a.next(), Some(&100)); // The separator. | |
597 | /// assert_eq!(a.next(), Some(&1)); // The next element from `a`. | |
598 | /// assert_eq!(a.next(), Some(&100)); // The separator. | |
599 | /// assert_eq!(a.next(), Some(&2)); // The last element from `a`. | |
600 | /// assert_eq!(a.next(), None); // The iterator is finished. | |
601 | /// ``` | |
602 | /// | |
603 | /// `intersperse` can be very useful to join an iterator's items using a common element: | |
94222f64 | 604 | /// ``` |
dc3f5686 XL |
605 | /// #![feature(iter_intersperse)] |
606 | /// | |
5869c6ff XL |
607 | /// let hello = ["Hello", "World", "!"].iter().copied().intersperse(" ").collect::<String>(); |
608 | /// assert_eq!(hello, "Hello World !"); | |
609 | /// ``` | |
610 | /// | |
611 | /// [`Clone`]: crate::clone::Clone | |
612 | /// [`intersperse_with`]: Iterator::intersperse_with | |
613 | #[inline] | |
dc3f5686 | 614 | #[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")] |
5869c6ff XL |
615 | fn intersperse(self, separator: Self::Item) -> Intersperse<Self> |
616 | where | |
617 | Self: Sized, | |
618 | Self::Item: Clone, | |
619 | { | |
620 | Intersperse::new(self, separator) | |
621 | } | |
622 | ||
623 | /// Creates a new iterator which places an item generated by `separator` | |
624 | /// between adjacent items of the original iterator. | |
625 | /// | |
626 | /// The closure will be called exactly once each time an item is placed | |
627 | /// between two adjacent items from the underlying iterator; specifically, | |
628 | /// the closure is not called if the underlying iterator yields less than | |
629 | /// two items and after the last item is yielded. | |
630 | /// | |
631 | /// If the iterator's item implements [`Clone`], it may be easier to use | |
632 | /// [`intersperse`]. | |
633 | /// | |
634 | /// # Examples | |
635 | /// | |
636 | /// Basic usage: | |
637 | /// | |
638 | /// ``` | |
dc3f5686 XL |
639 | /// #![feature(iter_intersperse)] |
640 | /// | |
5869c6ff XL |
641 | /// #[derive(PartialEq, Debug)] |
642 | /// struct NotClone(usize); | |
643 | /// | |
5099ac24 | 644 | /// let v = [NotClone(0), NotClone(1), NotClone(2)]; |
5869c6ff XL |
645 | /// let mut it = v.into_iter().intersperse_with(|| NotClone(99)); |
646 | /// | |
647 | /// assert_eq!(it.next(), Some(NotClone(0))); // The first element from `v`. | |
648 | /// assert_eq!(it.next(), Some(NotClone(99))); // The separator. | |
649 | /// assert_eq!(it.next(), Some(NotClone(1))); // The next element from `v`. | |
650 | /// assert_eq!(it.next(), Some(NotClone(99))); // The separator. | |
651 | /// assert_eq!(it.next(), Some(NotClone(2))); // The last element from from `v`. | |
652 | /// assert_eq!(it.next(), None); // The iterator is finished. | |
653 | /// ``` | |
654 | /// | |
655 | /// `intersperse_with` can be used in situations where the separator needs | |
656 | /// to be computed: | |
94222f64 | 657 | /// ``` |
dc3f5686 XL |
658 | /// #![feature(iter_intersperse)] |
659 | /// | |
5869c6ff XL |
660 | /// let src = ["Hello", "to", "all", "people", "!!"].iter().copied(); |
661 | /// | |
662 | /// // The closure mutably borrows its context to generate an item. | |
663 | /// let mut happy_emojis = [" ❤️ ", " 😀 "].iter().copied(); | |
664 | /// let separator = || happy_emojis.next().unwrap_or(" 🦀 "); | |
665 | /// | |
666 | /// let result = src.intersperse_with(separator).collect::<String>(); | |
667 | /// assert_eq!(result, "Hello ❤️ to 😀 all 🦀 people 🦀 !!"); | |
668 | /// ``` | |
669 | /// [`Clone`]: crate::clone::Clone | |
670 | /// [`intersperse`]: Iterator::intersperse | |
671 | #[inline] | |
dc3f5686 | 672 | #[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")] |
5869c6ff XL |
673 | fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G> |
674 | where | |
675 | Self: Sized, | |
676 | G: FnMut() -> Self::Item, | |
677 | { | |
678 | IntersperseWith::new(self, separator) | |
679 | } | |
680 | ||
a7813a04 XL |
681 | /// Takes a closure and creates an iterator which calls that closure on each |
682 | /// element. | |
683 | /// | |
684 | /// `map()` transforms one iterator into another, by means of its argument: | |
a1dfa0c6 | 685 | /// something that implements [`FnMut`]. It produces a new iterator which |
a7813a04 XL |
686 | /// calls this closure on each element of the original iterator. |
687 | /// | |
688 | /// If you are good at thinking in types, you can think of `map()` like this: | |
689 | /// If you have an iterator that gives you elements of some type `A`, and | |
690 | /// you want an iterator of some other type `B`, you can use `map()`, | |
691 | /// passing a closure that takes an `A` and returns a `B`. | |
692 | /// | |
693 | /// `map()` is conceptually similar to a [`for`] loop. However, as `map()` is | |
694 | /// lazy, it is best used when you're already working with other iterators. | |
695 | /// If you're doing some sort of looping for a side effect, it's considered | |
696 | /// more idiomatic to use [`for`] than `map()`. | |
697 | /// | |
13cf67c4 | 698 | /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for |
3dfed10e | 699 | /// [`FnMut`]: crate::ops::FnMut |
a7813a04 XL |
700 | /// |
701 | /// # Examples | |
702 | /// | |
703 | /// Basic usage: | |
704 | /// | |
705 | /// ``` | |
706 | /// let a = [1, 2, 3]; | |
707 | /// | |
48663c56 | 708 | /// let mut iter = a.iter().map(|x| 2 * x); |
a7813a04 XL |
709 | /// |
710 | /// assert_eq!(iter.next(), Some(2)); | |
711 | /// assert_eq!(iter.next(), Some(4)); | |
712 | /// assert_eq!(iter.next(), Some(6)); | |
713 | /// assert_eq!(iter.next(), None); | |
714 | /// ``` | |
715 | /// | |
716 | /// If you're doing some sort of side effect, prefer [`for`] to `map()`: | |
717 | /// | |
718 | /// ``` | |
719 | /// # #![allow(unused_must_use)] | |
720 | /// // don't do this: | |
5e7ed085 | 721 | /// (0..5).map(|x| println!("{x}")); |
a7813a04 XL |
722 | /// |
723 | /// // it won't even execute, as it is lazy. Rust will warn you about this. | |
724 | /// | |
725 | /// // Instead, use for: | |
726 | /// for x in 0..5 { | |
5e7ed085 | 727 | /// println!("{x}"); |
a7813a04 XL |
728 | /// } |
729 | /// ``` | |
730 | #[inline] | |
731 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
732 | fn map<B, F>(self, f: F) -> Map<Self, F> |
733 | where | |
734 | Self: Sized, | |
735 | F: FnMut(Self::Item) -> B, | |
a7813a04 | 736 | { |
9fa01778 | 737 | Map::new(self, f) |
a7813a04 XL |
738 | } |
739 | ||
041b39d2 XL |
740 | /// Calls a closure on each element of an iterator. |
741 | /// | |
742 | /// This is equivalent to using a [`for`] loop on the iterator, although | |
9fa01778 | 743 | /// `break` and `continue` are not possible from a closure. It's generally |
041b39d2 | 744 | /// more idiomatic to use a `for` loop, but `for_each` may be more legible |
9fa01778 | 745 | /// when processing items at the end of longer iterator chains. In some |
041b39d2 | 746 | /// cases `for_each` may also be faster than a loop, because it will use |
94222f64 | 747 | /// internal iteration on adapters like `Chain`. |
041b39d2 | 748 | /// |
13cf67c4 | 749 | /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for |
041b39d2 XL |
750 | /// |
751 | /// # Examples | |
752 | /// | |
753 | /// Basic usage: | |
754 | /// | |
755 | /// ``` | |
041b39d2 XL |
756 | /// use std::sync::mpsc::channel; |
757 | /// | |
758 | /// let (tx, rx) = channel(); | |
759 | /// (0..5).map(|x| x * 2 + 1) | |
760 | /// .for_each(move |x| tx.send(x).unwrap()); | |
761 | /// | |
762 | /// let v: Vec<_> = rx.iter().collect(); | |
763 | /// assert_eq!(v, vec![1, 3, 5, 7, 9]); | |
764 | /// ``` | |
765 | /// | |
766 | /// For such a small example, a `for` loop may be cleaner, but `for_each` | |
767 | /// might be preferable to keep a functional style with longer iterators: | |
768 | /// | |
769 | /// ``` | |
041b39d2 XL |
770 | /// (0..5).flat_map(|x| x * 100 .. x * 110) |
771 | /// .enumerate() | |
772 | /// .filter(|&(i, x)| (i + x) % 3 == 0) | |
5e7ed085 | 773 | /// .for_each(|(i, x)| println!("{i}:{x}")); |
041b39d2 XL |
774 | /// ``` |
775 | #[inline] | |
3b2f2976 | 776 | #[stable(feature = "iterator_for_each", since = "1.21.0")] |
dfeec247 XL |
777 | fn for_each<F>(self, f: F) |
778 | where | |
779 | Self: Sized, | |
780 | F: FnMut(Self::Item), | |
041b39d2 | 781 | { |
e1599b0c XL |
782 | #[inline] |
783 | fn call<T>(mut f: impl FnMut(T)) -> impl FnMut((), T) { | |
784 | move |(), item| f(item) | |
785 | } | |
786 | ||
787 | self.fold((), call(f)); | |
041b39d2 XL |
788 | } |
789 | ||
a7813a04 XL |
790 | /// Creates an iterator which uses a closure to determine if an element |
791 | /// should be yielded. | |
792 | /// | |
1b1a35ee XL |
793 | /// Given an element the closure must return `true` or `false`. The returned |
794 | /// iterator will yield only the elements for which the closure returns | |
795 | /// true. | |
a7813a04 XL |
796 | /// |
797 | /// # Examples | |
798 | /// | |
799 | /// Basic usage: | |
800 | /// | |
801 | /// ``` | |
802 | /// let a = [0i32, 1, 2]; | |
803 | /// | |
48663c56 | 804 | /// let mut iter = a.iter().filter(|x| x.is_positive()); |
a7813a04 XL |
805 | /// |
806 | /// assert_eq!(iter.next(), Some(&1)); | |
807 | /// assert_eq!(iter.next(), Some(&2)); | |
808 | /// assert_eq!(iter.next(), None); | |
809 | /// ``` | |
810 | /// | |
811 | /// Because the closure passed to `filter()` takes a reference, and many | |
812 | /// iterators iterate over references, this leads to a possibly confusing | |
813 | /// situation, where the type of the closure is a double reference: | |
814 | /// | |
815 | /// ``` | |
816 | /// let a = [0, 1, 2]; | |
817 | /// | |
48663c56 | 818 | /// let mut iter = a.iter().filter(|x| **x > 1); // need two *s! |
a7813a04 XL |
819 | /// |
820 | /// assert_eq!(iter.next(), Some(&2)); | |
821 | /// assert_eq!(iter.next(), None); | |
822 | /// ``` | |
823 | /// | |
824 | /// It's common to instead use destructuring on the argument to strip away | |
825 | /// one: | |
826 | /// | |
827 | /// ``` | |
828 | /// let a = [0, 1, 2]; | |
829 | /// | |
48663c56 | 830 | /// let mut iter = a.iter().filter(|&x| *x > 1); // both & and * |
a7813a04 XL |
831 | /// |
832 | /// assert_eq!(iter.next(), Some(&2)); | |
833 | /// assert_eq!(iter.next(), None); | |
834 | /// ``` | |
835 | /// | |
836 | /// or both: | |
837 | /// | |
838 | /// ``` | |
839 | /// let a = [0, 1, 2]; | |
840 | /// | |
48663c56 | 841 | /// let mut iter = a.iter().filter(|&&x| x > 1); // two &s |
a7813a04 XL |
842 | /// |
843 | /// assert_eq!(iter.next(), Some(&2)); | |
844 | /// assert_eq!(iter.next(), None); | |
845 | /// ``` | |
846 | /// | |
847 | /// of these layers. | |
74b04a01 XL |
848 | /// |
849 | /// Note that `iter.filter(f).next()` is equivalent to `iter.find(f)`. | |
a7813a04 XL |
850 | #[inline] |
851 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
852 | fn filter<P>(self, predicate: P) -> Filter<Self, P> |
853 | where | |
854 | Self: Sized, | |
855 | P: FnMut(&Self::Item) -> bool, | |
a7813a04 | 856 | { |
9fa01778 | 857 | Filter::new(self, predicate) |
a7813a04 XL |
858 | } |
859 | ||
860 | /// Creates an iterator that both filters and maps. | |
861 | /// | |
1b1a35ee XL |
862 | /// The returned iterator yields only the `value`s for which the supplied |
863 | /// closure returns `Some(value)`. | |
a7813a04 | 864 | /// |
1b1a35ee XL |
865 | /// `filter_map` can be used to make chains of [`filter`] and [`map`] more |
866 | /// concise. The example below shows how a `map().filter().map()` can be | |
867 | /// shortened to a single call to `filter_map`. | |
a7813a04 | 868 | /// |
1b1a35ee XL |
869 | /// [`filter`]: Iterator::filter |
870 | /// [`map`]: Iterator::map | |
a7813a04 XL |
871 | /// |
872 | /// # Examples | |
873 | /// | |
874 | /// Basic usage: | |
875 | /// | |
876 | /// ``` | |
3dfed10e | 877 | /// let a = ["1", "two", "NaN", "four", "5"]; |
a7813a04 XL |
878 | /// |
879 | /// let mut iter = a.iter().filter_map(|s| s.parse().ok()); | |
880 | /// | |
881 | /// assert_eq!(iter.next(), Some(1)); | |
ff7c6d11 | 882 | /// assert_eq!(iter.next(), Some(5)); |
a7813a04 XL |
883 | /// assert_eq!(iter.next(), None); |
884 | /// ``` | |
885 | /// | |
cc61c64b | 886 | /// Here's the same example, but with [`filter`] and [`map`]: |
a7813a04 XL |
887 | /// |
888 | /// ``` | |
3dfed10e | 889 | /// let a = ["1", "two", "NaN", "four", "5"]; |
ff7c6d11 | 890 | /// let mut iter = a.iter().map(|s| s.parse()).filter(|s| s.is_ok()).map(|s| s.unwrap()); |
3b2f2976 | 891 | /// assert_eq!(iter.next(), Some(1)); |
ff7c6d11 | 892 | /// assert_eq!(iter.next(), Some(5)); |
a7813a04 XL |
893 | /// assert_eq!(iter.next(), None); |
894 | /// ``` | |
a7813a04 XL |
895 | #[inline] |
896 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
897 | fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> |
898 | where | |
899 | Self: Sized, | |
900 | F: FnMut(Self::Item) -> Option<B>, | |
a7813a04 | 901 | { |
9fa01778 | 902 | FilterMap::new(self, f) |
a7813a04 XL |
903 | } |
904 | ||
905 | /// Creates an iterator which gives the current iteration count as well as | |
906 | /// the next value. | |
907 | /// | |
908 | /// The iterator returned yields pairs `(i, val)`, where `i` is the | |
909 | /// current index of iteration and `val` is the value returned by the | |
910 | /// iterator. | |
911 | /// | |
912 | /// `enumerate()` keeps its count as a [`usize`]. If you want to count by a | |
cc61c64b | 913 | /// different sized integer, the [`zip`] function provides similar |
a7813a04 XL |
914 | /// functionality. |
915 | /// | |
a7813a04 XL |
916 | /// # Overflow Behavior |
917 | /// | |
918 | /// The method does no guarding against overflows, so enumerating more than | |
919 | /// [`usize::MAX`] elements either produces the wrong result or panics. If | |
920 | /// debug assertions are enabled, a panic is guaranteed. | |
921 | /// | |
a7813a04 XL |
922 | /// # Panics |
923 | /// | |
924 | /// The returned iterator might panic if the to-be-returned index would | |
476ff2be SL |
925 | /// overflow a [`usize`]. |
926 | /// | |
1b1a35ee | 927 | /// [`zip`]: Iterator::zip |
a7813a04 XL |
928 | /// |
929 | /// # Examples | |
930 | /// | |
931 | /// ``` | |
932 | /// let a = ['a', 'b', 'c']; | |
933 | /// | |
934 | /// let mut iter = a.iter().enumerate(); | |
935 | /// | |
936 | /// assert_eq!(iter.next(), Some((0, &'a'))); | |
937 | /// assert_eq!(iter.next(), Some((1, &'b'))); | |
938 | /// assert_eq!(iter.next(), Some((2, &'c'))); | |
939 | /// assert_eq!(iter.next(), None); | |
940 | /// ``` | |
941 | #[inline] | |
942 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
943 | fn enumerate(self) -> Enumerate<Self> |
944 | where | |
945 | Self: Sized, | |
946 | { | |
9fa01778 | 947 | Enumerate::new(self) |
a7813a04 XL |
948 | } |
949 | ||
cdc7bbd5 XL |
950 | /// Creates an iterator which can use the [`peek`] and [`peek_mut`] methods |
951 | /// to look at the next element of the iterator without consuming it. See | |
952 | /// their documentation for more information. | |
a7813a04 | 953 | /// |
cdc7bbd5 XL |
954 | /// Note that the underlying iterator is still advanced when [`peek`] or |
955 | /// [`peek_mut`] are called for the first time: In order to retrieve the | |
956 | /// next element, [`next`] is called on the underlying iterator, hence any | |
957 | /// side effects (i.e. anything other than fetching the next value) of | |
958 | /// the [`next`] method will occur. | |
a7813a04 | 959 | /// |
a7813a04 XL |
960 | /// |
961 | /// # Examples | |
962 | /// | |
963 | /// Basic usage: | |
964 | /// | |
965 | /// ``` | |
966 | /// let xs = [1, 2, 3]; | |
967 | /// | |
968 | /// let mut iter = xs.iter().peekable(); | |
969 | /// | |
970 | /// // peek() lets us see into the future | |
971 | /// assert_eq!(iter.peek(), Some(&&1)); | |
972 | /// assert_eq!(iter.next(), Some(&1)); | |
973 | /// | |
974 | /// assert_eq!(iter.next(), Some(&2)); | |
975 | /// | |
976 | /// // we can peek() multiple times, the iterator won't advance | |
977 | /// assert_eq!(iter.peek(), Some(&&3)); | |
978 | /// assert_eq!(iter.peek(), Some(&&3)); | |
979 | /// | |
980 | /// assert_eq!(iter.next(), Some(&3)); | |
981 | /// | |
982 | /// // after the iterator is finished, so is peek() | |
983 | /// assert_eq!(iter.peek(), None); | |
984 | /// assert_eq!(iter.next(), None); | |
985 | /// ``` | |
cdc7bbd5 XL |
986 | /// |
987 | /// Using [`peek_mut`] to mutate the next item without advancing the | |
988 | /// iterator: | |
989 | /// | |
990 | /// ``` | |
991 | /// let xs = [1, 2, 3]; | |
992 | /// | |
993 | /// let mut iter = xs.iter().peekable(); | |
994 | /// | |
995 | /// // `peek_mut()` lets us see into the future | |
996 | /// assert_eq!(iter.peek_mut(), Some(&mut &1)); | |
997 | /// assert_eq!(iter.peek_mut(), Some(&mut &1)); | |
998 | /// assert_eq!(iter.next(), Some(&1)); | |
999 | /// | |
1000 | /// if let Some(mut p) = iter.peek_mut() { | |
1001 | /// assert_eq!(*p, &2); | |
1002 | /// // put a value into the iterator | |
1003 | /// *p = &1000; | |
1004 | /// } | |
1005 | /// | |
1006 | /// // The value reappears as the iterator continues | |
1007 | /// assert_eq!(iter.collect::<Vec<_>>(), vec![&1000, &3]); | |
1008 | /// ``` | |
1009 | /// [`peek`]: Peekable::peek | |
1010 | /// [`peek_mut`]: Peekable::peek_mut | |
1011 | /// [`next`]: Iterator::next | |
a7813a04 XL |
1012 | #[inline] |
1013 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
1014 | fn peekable(self) -> Peekable<Self> |
1015 | where | |
1016 | Self: Sized, | |
1017 | { | |
9fa01778 | 1018 | Peekable::new(self) |
a7813a04 XL |
1019 | } |
1020 | ||
cc61c64b | 1021 | /// Creates an iterator that [`skip`]s elements based on a predicate. |
a7813a04 | 1022 | /// |
1b1a35ee | 1023 | /// [`skip`]: Iterator::skip |
a7813a04 XL |
1024 | /// |
1025 | /// `skip_while()` takes a closure as an argument. It will call this | |
1026 | /// closure on each element of the iterator, and ignore elements | |
1027 | /// until it returns `false`. | |
1028 | /// | |
1029 | /// After `false` is returned, `skip_while()`'s job is over, and the | |
1030 | /// rest of the elements are yielded. | |
1031 | /// | |
1032 | /// # Examples | |
1033 | /// | |
1034 | /// Basic usage: | |
1035 | /// | |
1036 | /// ``` | |
1037 | /// let a = [-1i32, 0, 1]; | |
1038 | /// | |
48663c56 | 1039 | /// let mut iter = a.iter().skip_while(|x| x.is_negative()); |
a7813a04 XL |
1040 | /// |
1041 | /// assert_eq!(iter.next(), Some(&0)); | |
1042 | /// assert_eq!(iter.next(), Some(&1)); | |
1043 | /// assert_eq!(iter.next(), None); | |
1044 | /// ``` | |
1045 | /// | |
1046 | /// Because the closure passed to `skip_while()` takes a reference, and many | |
1047 | /// iterators iterate over references, this leads to a possibly confusing | |
6a06907d | 1048 | /// situation, where the type of the closure argument is a double reference: |
a7813a04 XL |
1049 | /// |
1050 | /// ``` | |
1051 | /// let a = [-1, 0, 1]; | |
1052 | /// | |
48663c56 | 1053 | /// let mut iter = a.iter().skip_while(|x| **x < 0); // need two *s! |
a7813a04 XL |
1054 | /// |
1055 | /// assert_eq!(iter.next(), Some(&0)); | |
1056 | /// assert_eq!(iter.next(), Some(&1)); | |
1057 | /// assert_eq!(iter.next(), None); | |
1058 | /// ``` | |
1059 | /// | |
1060 | /// Stopping after an initial `false`: | |
1061 | /// | |
1062 | /// ``` | |
1063 | /// let a = [-1, 0, 1, -2]; | |
1064 | /// | |
48663c56 | 1065 | /// let mut iter = a.iter().skip_while(|x| **x < 0); |
a7813a04 XL |
1066 | /// |
1067 | /// assert_eq!(iter.next(), Some(&0)); | |
1068 | /// assert_eq!(iter.next(), Some(&1)); | |
1069 | /// | |
1070 | /// // while this would have been false, since we already got a false, | |
1071 | /// // skip_while() isn't used any more | |
1072 | /// assert_eq!(iter.next(), Some(&-2)); | |
1073 | /// | |
1074 | /// assert_eq!(iter.next(), None); | |
1075 | /// ``` | |
1076 | #[inline] | |
a2a8927a | 1077 | #[doc(alias = "drop_while")] |
a7813a04 | 1078 | #[stable(feature = "rust1", since = "1.0.0")] |
dfeec247 XL |
1079 | fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> |
1080 | where | |
1081 | Self: Sized, | |
1082 | P: FnMut(&Self::Item) -> bool, | |
a7813a04 | 1083 | { |
9fa01778 | 1084 | SkipWhile::new(self, predicate) |
a7813a04 XL |
1085 | } |
1086 | ||
1087 | /// Creates an iterator that yields elements based on a predicate. | |
1088 | /// | |
1089 | /// `take_while()` takes a closure as an argument. It will call this | |
1090 | /// closure on each element of the iterator, and yield elements | |
1091 | /// while it returns `true`. | |
1092 | /// | |
1093 | /// After `false` is returned, `take_while()`'s job is over, and the | |
1094 | /// rest of the elements are ignored. | |
1095 | /// | |
1096 | /// # Examples | |
1097 | /// | |
1098 | /// Basic usage: | |
1099 | /// | |
1100 | /// ``` | |
1101 | /// let a = [-1i32, 0, 1]; | |
1102 | /// | |
48663c56 | 1103 | /// let mut iter = a.iter().take_while(|x| x.is_negative()); |
a7813a04 XL |
1104 | /// |
1105 | /// assert_eq!(iter.next(), Some(&-1)); | |
1106 | /// assert_eq!(iter.next(), None); | |
1107 | /// ``` | |
1108 | /// | |
1109 | /// Because the closure passed to `take_while()` takes a reference, and many | |
1110 | /// iterators iterate over references, this leads to a possibly confusing | |
1111 | /// situation, where the type of the closure is a double reference: | |
1112 | /// | |
1113 | /// ``` | |
1114 | /// let a = [-1, 0, 1]; | |
1115 | /// | |
48663c56 | 1116 | /// let mut iter = a.iter().take_while(|x| **x < 0); // need two *s! |
a7813a04 XL |
1117 | /// |
1118 | /// assert_eq!(iter.next(), Some(&-1)); | |
1119 | /// assert_eq!(iter.next(), None); | |
1120 | /// ``` | |
1121 | /// | |
1122 | /// Stopping after an initial `false`: | |
1123 | /// | |
1124 | /// ``` | |
1125 | /// let a = [-1, 0, 1, -2]; | |
1126 | /// | |
48663c56 | 1127 | /// let mut iter = a.iter().take_while(|x| **x < 0); |
a7813a04 XL |
1128 | /// |
1129 | /// assert_eq!(iter.next(), Some(&-1)); | |
1130 | /// | |
1131 | /// // We have more elements that are less than zero, but since we already | |
1132 | /// // got a false, take_while() isn't used any more | |
1133 | /// assert_eq!(iter.next(), None); | |
1134 | /// ``` | |
1135 | /// | |
1136 | /// Because `take_while()` needs to look at the value in order to see if it | |
1137 | /// should be included or not, consuming iterators will see that it is | |
1138 | /// removed: | |
1139 | /// | |
1140 | /// ``` | |
1141 | /// let a = [1, 2, 3, 4]; | |
48663c56 | 1142 | /// let mut iter = a.iter(); |
a7813a04 XL |
1143 | /// |
1144 | /// let result: Vec<i32> = iter.by_ref() | |
1145 | /// .take_while(|n| **n != 3) | |
1146 | /// .cloned() | |
1147 | /// .collect(); | |
1148 | /// | |
1149 | /// assert_eq!(result, &[1, 2]); | |
1150 | /// | |
1151 | /// let result: Vec<i32> = iter.cloned().collect(); | |
1152 | /// | |
1153 | /// assert_eq!(result, &[4]); | |
1154 | /// ``` | |
1155 | /// | |
1156 | /// The `3` is no longer there, because it was consumed in order to see if | |
9fa01778 | 1157 | /// the iteration should stop, but wasn't placed back into the iterator. |
a7813a04 XL |
1158 | #[inline] |
1159 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
1160 | fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> |
1161 | where | |
1162 | Self: Sized, | |
1163 | P: FnMut(&Self::Item) -> bool, | |
a7813a04 | 1164 | { |
9fa01778 | 1165 | TakeWhile::new(self, predicate) |
a7813a04 XL |
1166 | } |
1167 | ||
74b04a01 XL |
1168 | /// Creates an iterator that both yields elements based on a predicate and maps. |
1169 | /// | |
1170 | /// `map_while()` takes a closure as an argument. It will call this | |
1171 | /// closure on each element of the iterator, and yield elements | |
1172 | /// while it returns [`Some(_)`][`Some`]. | |
1173 | /// | |
74b04a01 XL |
1174 | /// # Examples |
1175 | /// | |
1176 | /// Basic usage: | |
1177 | /// | |
1178 | /// ``` | |
74b04a01 XL |
1179 | /// let a = [-1i32, 4, 0, 1]; |
1180 | /// | |
1181 | /// let mut iter = a.iter().map_while(|x| 16i32.checked_div(*x)); | |
1182 | /// | |
1183 | /// assert_eq!(iter.next(), Some(-16)); | |
1184 | /// assert_eq!(iter.next(), Some(4)); | |
1185 | /// assert_eq!(iter.next(), None); | |
1186 | /// ``` | |
1187 | /// | |
1188 | /// Here's the same example, but with [`take_while`] and [`map`]: | |
1189 | /// | |
1b1a35ee XL |
1190 | /// [`take_while`]: Iterator::take_while |
1191 | /// [`map`]: Iterator::map | |
74b04a01 XL |
1192 | /// |
1193 | /// ``` | |
1194 | /// let a = [-1i32, 4, 0, 1]; | |
1195 | /// | |
1196 | /// let mut iter = a.iter() | |
1197 | /// .map(|x| 16i32.checked_div(*x)) | |
1198 | /// .take_while(|x| x.is_some()) | |
1199 | /// .map(|x| x.unwrap()); | |
1200 | /// | |
1201 | /// assert_eq!(iter.next(), Some(-16)); | |
1202 | /// assert_eq!(iter.next(), Some(4)); | |
1203 | /// assert_eq!(iter.next(), None); | |
1204 | /// ``` | |
1205 | /// | |
1206 | /// Stopping after an initial [`None`]: | |
1207 | /// | |
1208 | /// ``` | |
ba9703b0 | 1209 | /// let a = [0, 1, 2, -3, 4, 5, -6]; |
74b04a01 | 1210 | /// |
ba9703b0 XL |
1211 | /// let iter = a.iter().map_while(|x| u32::try_from(*x).ok()); |
1212 | /// let vec = iter.collect::<Vec<_>>(); | |
74b04a01 | 1213 | /// |
ba9703b0 | 1214 | /// // We have more elements which could fit in u32 (4, 5), but `map_while` returned `None` for `-3` |
3dfed10e | 1215 | /// // (as the `predicate` returned `None`) and `collect` stops at the first `None` encountered. |
ba9703b0 | 1216 | /// assert_eq!(vec, vec![0, 1, 2]); |
74b04a01 XL |
1217 | /// ``` |
1218 | /// | |
1219 | /// Because `map_while()` needs to look at the value in order to see if it | |
1220 | /// should be included or not, consuming iterators will see that it is | |
1221 | /// removed: | |
1222 | /// | |
1223 | /// ``` | |
74b04a01 XL |
1224 | /// let a = [1, 2, -3, 4]; |
1225 | /// let mut iter = a.iter(); | |
1226 | /// | |
1227 | /// let result: Vec<u32> = iter.by_ref() | |
1228 | /// .map_while(|n| u32::try_from(*n).ok()) | |
1229 | /// .collect(); | |
1230 | /// | |
1231 | /// assert_eq!(result, &[1, 2]); | |
1232 | /// | |
1233 | /// let result: Vec<i32> = iter.cloned().collect(); | |
1234 | /// | |
1235 | /// assert_eq!(result, &[4]); | |
1236 | /// ``` | |
1237 | /// | |
1238 | /// The `-3` is no longer there, because it was consumed in order to see if | |
1239 | /// the iteration should stop, but wasn't placed back into the iterator. | |
1240 | /// | |
ba9703b0 | 1241 | /// Note that unlike [`take_while`] this iterator is **not** fused. |
5869c6ff | 1242 | /// It is also not specified what this iterator returns after the first [`None`] is returned. |
ba9703b0 XL |
1243 | /// If you need fused iterator, use [`fuse`]. |
1244 | /// | |
1b1a35ee | 1245 | /// [`fuse`]: Iterator::fuse |
74b04a01 | 1246 | #[inline] |
c295e0f8 | 1247 | #[stable(feature = "iter_map_while", since = "1.57.0")] |
74b04a01 XL |
1248 | fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> |
1249 | where | |
1250 | Self: Sized, | |
1251 | P: FnMut(Self::Item) -> Option<B>, | |
1252 | { | |
1253 | MapWhile::new(self, predicate) | |
1254 | } | |
1255 | ||
a7813a04 XL |
1256 | /// Creates an iterator that skips the first `n` elements. |
1257 | /// | |
cdc7bbd5 XL |
1258 | /// `skip(n)` skips elements until `n` elements are skipped or the end of the |
1259 | /// iterator is reached (whichever happens first). After that, all the remaining | |
1260 | /// elements are yielded. In particular, if the original iterator is too short, | |
1261 | /// then the returned iterator is empty. | |
1262 | /// | |
dc9dc135 | 1263 | /// Rather than overriding this method directly, instead override the `nth` method. |
a7813a04 XL |
1264 | /// |
1265 | /// # Examples | |
1266 | /// | |
1267 | /// Basic usage: | |
1268 | /// | |
1269 | /// ``` | |
1270 | /// let a = [1, 2, 3]; | |
1271 | /// | |
1272 | /// let mut iter = a.iter().skip(2); | |
1273 | /// | |
1274 | /// assert_eq!(iter.next(), Some(&3)); | |
1275 | /// assert_eq!(iter.next(), None); | |
1276 | /// ``` | |
1277 | #[inline] | |
1278 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
1279 | fn skip(self, n: usize) -> Skip<Self> |
1280 | where | |
1281 | Self: Sized, | |
1282 | { | |
9fa01778 | 1283 | Skip::new(self, n) |
a7813a04 XL |
1284 | } |
1285 | ||
cdc7bbd5 XL |
1286 | /// Creates an iterator that yields the first `n` elements, or fewer |
1287 | /// if the underlying iterator ends sooner. | |
1288 | /// | |
1289 | /// `take(n)` yields elements until `n` elements are yielded or the end of | |
1290 | /// the iterator is reached (whichever happens first). | |
1291 | /// The returned iterator is a prefix of length `n` if the original iterator | |
1292 | /// contains at least `n` elements, otherwise it contains all of the | |
1293 | /// (fewer than `n`) elements of the original iterator. | |
a7813a04 XL |
1294 | /// |
1295 | /// # Examples | |
1296 | /// | |
1297 | /// Basic usage: | |
1298 | /// | |
1299 | /// ``` | |
1300 | /// let a = [1, 2, 3]; | |
1301 | /// | |
1302 | /// let mut iter = a.iter().take(2); | |
1303 | /// | |
1304 | /// assert_eq!(iter.next(), Some(&1)); | |
1305 | /// assert_eq!(iter.next(), Some(&2)); | |
1306 | /// assert_eq!(iter.next(), None); | |
1307 | /// ``` | |
1308 | /// | |
1309 | /// `take()` is often used with an infinite iterator, to make it finite: | |
1310 | /// | |
1311 | /// ``` | |
1312 | /// let mut iter = (0..).take(3); | |
1313 | /// | |
1314 | /// assert_eq!(iter.next(), Some(0)); | |
1315 | /// assert_eq!(iter.next(), Some(1)); | |
1316 | /// assert_eq!(iter.next(), Some(2)); | |
1317 | /// assert_eq!(iter.next(), None); | |
1318 | /// ``` | |
f9f354fc XL |
1319 | /// |
1320 | /// If less than `n` elements are available, | |
1321 | /// `take` will limit itself to the size of the underlying iterator: | |
1322 | /// | |
1323 | /// ``` | |
5099ac24 | 1324 | /// let v = [1, 2]; |
f9f354fc XL |
1325 | /// let mut iter = v.into_iter().take(5); |
1326 | /// assert_eq!(iter.next(), Some(1)); | |
1327 | /// assert_eq!(iter.next(), Some(2)); | |
1328 | /// assert_eq!(iter.next(), None); | |
1329 | /// ``` | |
a7813a04 XL |
1330 | #[inline] |
1331 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
1332 | fn take(self, n: usize) -> Take<Self> |
1333 | where | |
1334 | Self: Sized, | |
1335 | { | |
9fa01778 | 1336 | Take::new(self, n) |
a7813a04 XL |
1337 | } |
1338 | ||
94222f64 | 1339 | /// An iterator adapter similar to [`fold`] that holds internal state and |
a7813a04 XL |
1340 | /// produces a new iterator. |
1341 | /// | |
1b1a35ee | 1342 | /// [`fold`]: Iterator::fold |
a7813a04 XL |
1343 | /// |
1344 | /// `scan()` takes two arguments: an initial value which seeds the internal | |
1345 | /// state, and a closure with two arguments, the first being a mutable | |
1346 | /// reference to the internal state and the second an iterator element. | |
1347 | /// The closure can assign to the internal state to share state between | |
1348 | /// iterations. | |
1349 | /// | |
1350 | /// On iteration, the closure will be applied to each element of the | |
1351 | /// iterator and the return value from the closure, an [`Option`], is | |
1352 | /// yielded by the iterator. | |
1353 | /// | |
a7813a04 XL |
1354 | /// # Examples |
1355 | /// | |
1356 | /// Basic usage: | |
1357 | /// | |
1358 | /// ``` | |
1359 | /// let a = [1, 2, 3]; | |
1360 | /// | |
1361 | /// let mut iter = a.iter().scan(1, |state, &x| { | |
1362 | /// // each iteration, we'll multiply the state by the element | |
1363 | /// *state = *state * x; | |
1364 | /// | |
0531ce1d XL |
1365 | /// // then, we'll yield the negation of the state |
1366 | /// Some(-*state) | |
a7813a04 XL |
1367 | /// }); |
1368 | /// | |
0531ce1d XL |
1369 | /// assert_eq!(iter.next(), Some(-1)); |
1370 | /// assert_eq!(iter.next(), Some(-2)); | |
1371 | /// assert_eq!(iter.next(), Some(-6)); | |
a7813a04 XL |
1372 | /// assert_eq!(iter.next(), None); |
1373 | /// ``` | |
1374 | #[inline] | |
1375 | #[stable(feature = "rust1", since = "1.0.0")] | |
1376 | fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> | |
dfeec247 XL |
1377 | where |
1378 | Self: Sized, | |
1379 | F: FnMut(&mut St, Self::Item) -> Option<B>, | |
a7813a04 | 1380 | { |
9fa01778 | 1381 | Scan::new(self, initial_state, f) |
a7813a04 XL |
1382 | } |
1383 | ||
1384 | /// Creates an iterator that works like map, but flattens nested structure. | |
1385 | /// | |
cc61c64b | 1386 | /// The [`map`] adapter is very useful, but only when the closure |
a7813a04 XL |
1387 | /// argument produces values. If it produces an iterator instead, there's |
1388 | /// an extra layer of indirection. `flat_map()` will remove this extra layer | |
1389 | /// on its own. | |
1390 | /// | |
83c7162d | 1391 | /// You can think of `flat_map(f)` as the semantic equivalent |
0531ce1d XL |
1392 | /// of [`map`]ping, and then [`flatten`]ing as in `map(f).flatten()`. |
1393 | /// | |
cc61c64b | 1394 | /// Another way of thinking about `flat_map()`: [`map`]'s closure returns |
a7813a04 XL |
1395 | /// one item for each element, and `flat_map()`'s closure returns an |
1396 | /// iterator for each element. | |
1397 | /// | |
1b1a35ee XL |
1398 | /// [`map`]: Iterator::map |
1399 | /// [`flatten`]: Iterator::flatten | |
476ff2be | 1400 | /// |
a7813a04 XL |
1401 | /// # Examples |
1402 | /// | |
1403 | /// Basic usage: | |
1404 | /// | |
1405 | /// ``` | |
1406 | /// let words = ["alpha", "beta", "gamma"]; | |
1407 | /// | |
1408 | /// // chars() returns an iterator | |
1409 | /// let merged: String = words.iter() | |
1410 | /// .flat_map(|s| s.chars()) | |
1411 | /// .collect(); | |
1412 | /// assert_eq!(merged, "alphabetagamma"); | |
1413 | /// ``` | |
1414 | #[inline] | |
1415 | #[stable(feature = "rust1", since = "1.0.0")] | |
1416 | fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> | |
dfeec247 XL |
1417 | where |
1418 | Self: Sized, | |
1419 | U: IntoIterator, | |
1420 | F: FnMut(Self::Item) -> U, | |
a7813a04 | 1421 | { |
9fa01778 | 1422 | FlatMap::new(self, f) |
0531ce1d XL |
1423 | } |
1424 | ||
1425 | /// Creates an iterator that flattens nested structure. | |
1426 | /// | |
1427 | /// This is useful when you have an iterator of iterators or an iterator of | |
1428 | /// things that can be turned into iterators and you want to remove one | |
1429 | /// level of indirection. | |
1430 | /// | |
1431 | /// # Examples | |
1432 | /// | |
1433 | /// Basic usage: | |
1434 | /// | |
1435 | /// ``` | |
0531ce1d XL |
1436 | /// let data = vec![vec![1, 2, 3, 4], vec![5, 6]]; |
1437 | /// let flattened = data.into_iter().flatten().collect::<Vec<u8>>(); | |
1438 | /// assert_eq!(flattened, &[1, 2, 3, 4, 5, 6]); | |
1439 | /// ``` | |
1440 | /// | |
1441 | /// Mapping and then flattening: | |
1442 | /// | |
1443 | /// ``` | |
0531ce1d XL |
1444 | /// let words = ["alpha", "beta", "gamma"]; |
1445 | /// | |
1446 | /// // chars() returns an iterator | |
1447 | /// let merged: String = words.iter() | |
1448 | /// .map(|s| s.chars()) | |
1449 | /// .flatten() | |
1450 | /// .collect(); | |
1451 | /// assert_eq!(merged, "alphabetagamma"); | |
1452 | /// ``` | |
1453 | /// | |
1454 | /// You can also rewrite this in terms of [`flat_map()`], which is preferable | |
1455 | /// in this case since it conveys intent more clearly: | |
1456 | /// | |
1457 | /// ``` | |
1458 | /// let words = ["alpha", "beta", "gamma"]; | |
1459 | /// | |
1460 | /// // chars() returns an iterator | |
1461 | /// let merged: String = words.iter() | |
1462 | /// .flat_map(|s| s.chars()) | |
1463 | /// .collect(); | |
1464 | /// assert_eq!(merged, "alphabetagamma"); | |
1465 | /// ``` | |
1466 | /// | |
fc512014 | 1467 | /// Flattening only removes one level of nesting at a time: |
0531ce1d XL |
1468 | /// |
1469 | /// ``` | |
0531ce1d XL |
1470 | /// let d3 = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]; |
1471 | /// | |
1472 | /// let d2 = d3.iter().flatten().collect::<Vec<_>>(); | |
1473 | /// assert_eq!(d2, [&[1, 2], &[3, 4], &[5, 6], &[7, 8]]); | |
1474 | /// | |
1475 | /// let d1 = d3.iter().flatten().flatten().collect::<Vec<_>>(); | |
1476 | /// assert_eq!(d1, [&1, &2, &3, &4, &5, &6, &7, &8]); | |
1477 | /// ``` | |
1478 | /// | |
1479 | /// Here we see that `flatten()` does not perform a "deep" flatten. | |
1480 | /// Instead, only one level of nesting is removed. That is, if you | |
fc512014 | 1481 | /// `flatten()` a three-dimensional array, the result will be |
0531ce1d XL |
1482 | /// two-dimensional and not one-dimensional. To get a one-dimensional |
1483 | /// structure, you have to `flatten()` again. | |
83c7162d | 1484 | /// |
1b1a35ee | 1485 | /// [`flat_map()`]: Iterator::flat_map |
0531ce1d | 1486 | #[inline] |
b7449926 | 1487 | #[stable(feature = "iterator_flatten", since = "1.29.0")] |
0531ce1d | 1488 | fn flatten(self) -> Flatten<Self> |
dfeec247 XL |
1489 | where |
1490 | Self: Sized, | |
1491 | Self::Item: IntoIterator, | |
1492 | { | |
9fa01778 | 1493 | Flatten::new(self) |
a7813a04 XL |
1494 | } |
1495 | ||
476ff2be SL |
1496 | /// Creates an iterator which ends after the first [`None`]. |
1497 | /// | |
1498 | /// After an iterator returns [`None`], future calls may or may not yield | |
1499 | /// [`Some(T)`] again. `fuse()` adapts an iterator, ensuring that after a | |
1500 | /// [`None`] is given, it will always return [`None`] forever. | |
a7813a04 | 1501 | /// |
cdc7bbd5 XL |
1502 | /// Note that the [`Fuse`] wrapper is a no-op on iterators that implement |
1503 | /// the [`FusedIterator`] trait. `fuse()` may therefore behave incorrectly | |
1504 | /// if the [`FusedIterator`] trait is improperly implemented. | |
1505 | /// | |
3dfed10e | 1506 | /// [`Some(T)`]: Some |
cdc7bbd5 | 1507 | /// [`FusedIterator`]: crate::iter::FusedIterator |
a7813a04 XL |
1508 | /// |
1509 | /// # Examples | |
1510 | /// | |
1511 | /// Basic usage: | |
1512 | /// | |
1513 | /// ``` | |
1514 | /// // an iterator which alternates between Some and None | |
1515 | /// struct Alternate { | |
1516 | /// state: i32, | |
1517 | /// } | |
1518 | /// | |
1519 | /// impl Iterator for Alternate { | |
1520 | /// type Item = i32; | |
1521 | /// | |
1522 | /// fn next(&mut self) -> Option<i32> { | |
1523 | /// let val = self.state; | |
1524 | /// self.state = self.state + 1; | |
1525 | /// | |
1526 | /// // if it's even, Some(i32), else None | |
1527 | /// if val % 2 == 0 { | |
1528 | /// Some(val) | |
1529 | /// } else { | |
1530 | /// None | |
1531 | /// } | |
1532 | /// } | |
1533 | /// } | |
1534 | /// | |
1535 | /// let mut iter = Alternate { state: 0 }; | |
1536 | /// | |
1537 | /// // we can see our iterator going back and forth | |
1538 | /// assert_eq!(iter.next(), Some(0)); | |
1539 | /// assert_eq!(iter.next(), None); | |
1540 | /// assert_eq!(iter.next(), Some(2)); | |
1541 | /// assert_eq!(iter.next(), None); | |
1542 | /// | |
1543 | /// // however, once we fuse it... | |
1544 | /// let mut iter = iter.fuse(); | |
1545 | /// | |
1546 | /// assert_eq!(iter.next(), Some(4)); | |
1547 | /// assert_eq!(iter.next(), None); | |
1548 | /// | |
9fa01778 | 1549 | /// // it will always return `None` after the first time. |
a7813a04 XL |
1550 | /// assert_eq!(iter.next(), None); |
1551 | /// assert_eq!(iter.next(), None); | |
1552 | /// assert_eq!(iter.next(), None); | |
1553 | /// ``` | |
1554 | #[inline] | |
1555 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
1556 | fn fuse(self) -> Fuse<Self> |
1557 | where | |
1558 | Self: Sized, | |
1559 | { | |
9fa01778 | 1560 | Fuse::new(self) |
a7813a04 XL |
1561 | } |
1562 | ||
60c5eb7d | 1563 | /// Does something with each element of an iterator, passing the value on. |
a7813a04 XL |
1564 | /// |
1565 | /// When using iterators, you'll often chain several of them together. | |
1566 | /// While working on such code, you might want to check out what's | |
1567 | /// happening at various parts in the pipeline. To do that, insert | |
1568 | /// a call to `inspect()`. | |
1569 | /// | |
94b46f34 XL |
1570 | /// It's more common for `inspect()` to be used as a debugging tool than to |
1571 | /// exist in your final code, but applications may find it useful in certain | |
1572 | /// situations when errors need to be logged before being discarded. | |
a7813a04 XL |
1573 | /// |
1574 | /// # Examples | |
1575 | /// | |
1576 | /// Basic usage: | |
1577 | /// | |
1578 | /// ``` | |
1579 | /// let a = [1, 4, 2, 3]; | |
1580 | /// | |
1581 | /// // this iterator sequence is complex. | |
1582 | /// let sum = a.iter() | |
0531ce1d XL |
1583 | /// .cloned() |
1584 | /// .filter(|x| x % 2 == 0) | |
1585 | /// .fold(0, |sum, i| sum + i); | |
a7813a04 | 1586 | /// |
5e7ed085 | 1587 | /// println!("{sum}"); |
a7813a04 XL |
1588 | /// |
1589 | /// // let's add some inspect() calls to investigate what's happening | |
1590 | /// let sum = a.iter() | |
0531ce1d | 1591 | /// .cloned() |
5e7ed085 | 1592 | /// .inspect(|x| println!("about to filter: {x}")) |
0531ce1d | 1593 | /// .filter(|x| x % 2 == 0) |
5e7ed085 | 1594 | /// .inspect(|x| println!("made it through filter: {x}")) |
0531ce1d | 1595 | /// .fold(0, |sum, i| sum + i); |
a7813a04 | 1596 | /// |
5e7ed085 | 1597 | /// println!("{sum}"); |
a7813a04 XL |
1598 | /// ``` |
1599 | /// | |
1600 | /// This will print: | |
1601 | /// | |
1602 | /// ```text | |
0531ce1d | 1603 | /// 6 |
a7813a04 XL |
1604 | /// about to filter: 1 |
1605 | /// about to filter: 4 | |
1606 | /// made it through filter: 4 | |
1607 | /// about to filter: 2 | |
1608 | /// made it through filter: 2 | |
1609 | /// about to filter: 3 | |
1610 | /// 6 | |
1611 | /// ``` | |
94b46f34 XL |
1612 | /// |
1613 | /// Logging errors before discarding them: | |
1614 | /// | |
1615 | /// ``` | |
1616 | /// let lines = ["1", "2", "a"]; | |
1617 | /// | |
1618 | /// let sum: i32 = lines | |
1619 | /// .iter() | |
1620 | /// .map(|line| line.parse::<i32>()) | |
1621 | /// .inspect(|num| { | |
1622 | /// if let Err(ref e) = *num { | |
5e7ed085 | 1623 | /// println!("Parsing error: {e}"); |
94b46f34 XL |
1624 | /// } |
1625 | /// }) | |
1626 | /// .filter_map(Result::ok) | |
1627 | /// .sum(); | |
1628 | /// | |
5e7ed085 | 1629 | /// println!("Sum: {sum}"); |
94b46f34 XL |
1630 | /// ``` |
1631 | /// | |
1632 | /// This will print: | |
1633 | /// | |
1634 | /// ```text | |
1635 | /// Parsing error: invalid digit found in string | |
1636 | /// Sum: 3 | |
1637 | /// ``` | |
a7813a04 XL |
1638 | #[inline] |
1639 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
1640 | fn inspect<F>(self, f: F) -> Inspect<Self, F> |
1641 | where | |
1642 | Self: Sized, | |
1643 | F: FnMut(&Self::Item), | |
a7813a04 | 1644 | { |
9fa01778 | 1645 | Inspect::new(self, f) |
a7813a04 XL |
1646 | } |
1647 | ||
1648 | /// Borrows an iterator, rather than consuming it. | |
1649 | /// | |
94222f64 | 1650 | /// This is useful to allow applying iterator adapters while still |
a7813a04 XL |
1651 | /// retaining ownership of the original iterator. |
1652 | /// | |
1653 | /// # Examples | |
1654 | /// | |
1655 | /// Basic usage: | |
1656 | /// | |
1657 | /// ``` | |
5099ac24 | 1658 | /// let mut words = ["hello", "world", "of", "Rust"].into_iter(); |
a7813a04 | 1659 | /// |
cdc7bbd5 XL |
1660 | /// // Take the first two words. |
1661 | /// let hello_world: Vec<_> = words.by_ref().take(2).collect(); | |
1662 | /// assert_eq!(hello_world, vec!["hello", "world"]); | |
a7813a04 | 1663 | /// |
cdc7bbd5 XL |
1664 | /// // Collect the rest of the words. |
1665 | /// // We can only do this because we used `by_ref` earlier. | |
1666 | /// let of_rust: Vec<_> = words.collect(); | |
1667 | /// assert_eq!(of_rust, vec!["of", "Rust"]); | |
a7813a04 XL |
1668 | /// ``` |
1669 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
1670 | fn by_ref(&mut self) -> &mut Self |
1671 | where | |
1672 | Self: Sized, | |
1673 | { | |
1674 | self | |
1675 | } | |
a7813a04 XL |
1676 | |
1677 | /// Transforms an iterator into a collection. | |
1678 | /// | |
1679 | /// `collect()` can take anything iterable, and turn it into a relevant | |
1680 | /// collection. This is one of the more powerful methods in the standard | |
1681 | /// library, used in a variety of contexts. | |
1682 | /// | |
1683 | /// The most basic pattern in which `collect()` is used is to turn one | |
cc61c64b | 1684 | /// collection into another. You take a collection, call [`iter`] on it, |
a7813a04 XL |
1685 | /// do a bunch of transformations, and then `collect()` at the end. |
1686 | /// | |
3dfed10e XL |
1687 | /// `collect()` can also create instances of types that are not typical |
1688 | /// collections. For example, a [`String`] can be built from [`char`]s, | |
1689 | /// and an iterator of [`Result<T, E>`][`Result`] items can be collected | |
1690 | /// into `Result<Collection<T>, E>`. See the examples below for more. | |
a7813a04 | 1691 | /// |
a7813a04 XL |
1692 | /// Because `collect()` is so general, it can cause problems with type |
1693 | /// inference. As such, `collect()` is one of the few times you'll see | |
1694 | /// the syntax affectionately known as the 'turbofish': `::<>`. This | |
1695 | /// helps the inference algorithm understand specifically which collection | |
1696 | /// you're trying to collect into. | |
1697 | /// | |
1698 | /// # Examples | |
1699 | /// | |
1700 | /// Basic usage: | |
1701 | /// | |
1702 | /// ``` | |
1703 | /// let a = [1, 2, 3]; | |
1704 | /// | |
1705 | /// let doubled: Vec<i32> = a.iter() | |
1706 | /// .map(|&x| x * 2) | |
1707 | /// .collect(); | |
1708 | /// | |
1709 | /// assert_eq!(vec![2, 4, 6], doubled); | |
1710 | /// ``` | |
1711 | /// | |
1712 | /// Note that we needed the `: Vec<i32>` on the left-hand side. This is because | |
1713 | /// we could collect into, for example, a [`VecDeque<T>`] instead: | |
1714 | /// | |
1715 | /// [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html | |
1716 | /// | |
1717 | /// ``` | |
1718 | /// use std::collections::VecDeque; | |
1719 | /// | |
1720 | /// let a = [1, 2, 3]; | |
1721 | /// | |
0531ce1d | 1722 | /// let doubled: VecDeque<i32> = a.iter().map(|&x| x * 2).collect(); |
a7813a04 XL |
1723 | /// |
1724 | /// assert_eq!(2, doubled[0]); | |
1725 | /// assert_eq!(4, doubled[1]); | |
1726 | /// assert_eq!(6, doubled[2]); | |
1727 | /// ``` | |
1728 | /// | |
1729 | /// Using the 'turbofish' instead of annotating `doubled`: | |
1730 | /// | |
1731 | /// ``` | |
1732 | /// let a = [1, 2, 3]; | |
1733 | /// | |
0531ce1d | 1734 | /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<i32>>(); |
a7813a04 XL |
1735 | /// |
1736 | /// assert_eq!(vec![2, 4, 6], doubled); | |
1737 | /// ``` | |
1738 | /// | |
3b2f2976 | 1739 | /// Because `collect()` only cares about what you're collecting into, you can |
a7813a04 XL |
1740 | /// still use a partial type hint, `_`, with the turbofish: |
1741 | /// | |
1742 | /// ``` | |
1743 | /// let a = [1, 2, 3]; | |
1744 | /// | |
0531ce1d | 1745 | /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<_>>(); |
a7813a04 XL |
1746 | /// |
1747 | /// assert_eq!(vec![2, 4, 6], doubled); | |
1748 | /// ``` | |
1749 | /// | |
1750 | /// Using `collect()` to make a [`String`]: | |
1751 | /// | |
1752 | /// ``` | |
1753 | /// let chars = ['g', 'd', 'k', 'k', 'n']; | |
1754 | /// | |
1755 | /// let hello: String = chars.iter() | |
0531ce1d XL |
1756 | /// .map(|&x| x as u8) |
1757 | /// .map(|x| (x + 1) as char) | |
1758 | /// .collect(); | |
a7813a04 XL |
1759 | /// |
1760 | /// assert_eq!("hello", hello); | |
1761 | /// ``` | |
1762 | /// | |
476ff2be | 1763 | /// If you have a list of [`Result<T, E>`][`Result`]s, you can use `collect()` to |
a7813a04 XL |
1764 | /// see if any of them failed: |
1765 | /// | |
1766 | /// ``` | |
1767 | /// let results = [Ok(1), Err("nope"), Ok(3), Err("bad")]; | |
1768 | /// | |
1769 | /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect(); | |
1770 | /// | |
1771 | /// // gives us the first error | |
1772 | /// assert_eq!(Err("nope"), result); | |
1773 | /// | |
1774 | /// let results = [Ok(1), Ok(3)]; | |
1775 | /// | |
1776 | /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect(); | |
1777 | /// | |
1778 | /// // gives us the list of answers | |
1779 | /// assert_eq!(Ok(vec![1, 3]), result); | |
1780 | /// ``` | |
476ff2be | 1781 | /// |
1b1a35ee | 1782 | /// [`iter`]: Iterator::next |
476ff2be | 1783 | /// [`String`]: ../../std/string/struct.String.html |
3dfed10e | 1784 | /// [`char`]: type@char |
a7813a04 XL |
1785 | #[inline] |
1786 | #[stable(feature = "rust1", since = "1.0.0")] | |
83c7162d | 1787 | #[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"] |
dfeec247 XL |
1788 | fn collect<B: FromIterator<Self::Item>>(self) -> B |
1789 | where | |
1790 | Self: Sized, | |
1791 | { | |
a7813a04 XL |
1792 | FromIterator::from_iter(self) |
1793 | } | |
1794 | ||
5099ac24 FG |
1795 | /// Fallibly transforms an iterator into a collection, short circuiting if |
1796 | /// a failure is encountered. | |
1797 | /// | |
1798 | /// `try_collect()` is a variation of [`collect()`][`collect`] that allows fallible | |
1799 | /// conversions during collection. Its main use case is simplifying conversions from | |
1800 | /// iterators yielding [`Option<T>`][`Option`] into `Option<Collection<T>>`, or similarly for other [`Try`] | |
1801 | /// types (e.g. [`Result`]). | |
1802 | /// | |
1803 | /// Importantly, `try_collect()` doesn't require that the outer [`Try`] type also implements [`FromIterator`]; | |
1804 | /// only the inner type produced on `Try::Output` must implement it. Concretely, | |
1805 | /// this means that collecting into `ControlFlow<_, Vec<i32>>` is valid because `Vec<i32>` implements | |
1806 | /// [`FromIterator`], even though [`ControlFlow`] doesn't. | |
1807 | /// | |
1808 | /// Also, if a failure is encountered during `try_collect()`, the iterator is still valid and | |
1809 | /// may continue to be used, in which case it will continue iterating starting after the element that | |
1810 | /// triggered the failure. See the last example below for an example of how this works. | |
1811 | /// | |
1812 | /// # Examples | |
1813 | /// Successfully collecting an iterator of `Option<i32>` into `Option<Vec<i32>>`: | |
1814 | /// ``` | |
1815 | /// #![feature(iterator_try_collect)] | |
1816 | /// | |
1817 | /// let u = vec![Some(1), Some(2), Some(3)]; | |
1818 | /// let v = u.into_iter().try_collect::<Vec<i32>>(); | |
1819 | /// assert_eq!(v, Some(vec![1, 2, 3])); | |
1820 | /// ``` | |
1821 | /// | |
1822 | /// Failing to collect in the same way: | |
1823 | /// ``` | |
1824 | /// #![feature(iterator_try_collect)] | |
1825 | /// | |
1826 | /// let u = vec![Some(1), Some(2), None, Some(3)]; | |
1827 | /// let v = u.into_iter().try_collect::<Vec<i32>>(); | |
1828 | /// assert_eq!(v, None); | |
1829 | /// ``` | |
1830 | /// | |
1831 | /// A similar example, but with `Result`: | |
1832 | /// ``` | |
1833 | /// #![feature(iterator_try_collect)] | |
1834 | /// | |
1835 | /// let u: Vec<Result<i32, ()>> = vec![Ok(1), Ok(2), Ok(3)]; | |
1836 | /// let v = u.into_iter().try_collect::<Vec<i32>>(); | |
1837 | /// assert_eq!(v, Ok(vec![1, 2, 3])); | |
1838 | /// | |
1839 | /// let u = vec![Ok(1), Ok(2), Err(()), Ok(3)]; | |
1840 | /// let v = u.into_iter().try_collect::<Vec<i32>>(); | |
1841 | /// assert_eq!(v, Err(())); | |
1842 | /// ``` | |
1843 | /// | |
1844 | /// Finally, even [`ControlFlow`] works, despite the fact that it | |
1845 | /// doesn't implement [`FromIterator`]. Note also that the iterator can | |
1846 | /// continue to be used, even if a failure is encountered: | |
1847 | /// | |
1848 | /// ``` | |
1849 | /// #![feature(iterator_try_collect)] | |
1850 | /// | |
1851 | /// use core::ops::ControlFlow::{Break, Continue}; | |
1852 | /// | |
1853 | /// let u = [Continue(1), Continue(2), Break(3), Continue(4), Continue(5)]; | |
1854 | /// let mut it = u.into_iter(); | |
1855 | /// | |
1856 | /// let v = it.try_collect::<Vec<_>>(); | |
1857 | /// assert_eq!(v, Break(3)); | |
1858 | /// | |
1859 | /// let v = it.try_collect::<Vec<_>>(); | |
1860 | /// assert_eq!(v, Continue(vec![4, 5])); | |
1861 | /// ``` | |
1862 | /// | |
1863 | /// [`collect`]: Iterator::collect | |
1864 | #[inline] | |
1865 | #[unstable(feature = "iterator_try_collect", issue = "94047")] | |
1866 | fn try_collect<B>(&mut self) -> ChangeOutputType<Self::Item, B> | |
1867 | where | |
1868 | Self: Sized, | |
1869 | <Self as Iterator>::Item: Try, | |
1870 | <<Self as Iterator>::Item as Try>::Residual: Residual<B>, | |
1871 | B: FromIterator<<Self::Item as Try>::Output>, | |
1872 | { | |
5e7ed085 FG |
1873 | try_process(ByRefSized(self), |i| i.collect()) |
1874 | } | |
1875 | ||
1876 | /// Collects all the items from an iterator into a collection. | |
1877 | /// | |
1878 | /// This method consumes the iterator and adds all its items to the | |
1879 | /// passed collection. The collection is then returned, so the call chain | |
1880 | /// can be continued. | |
1881 | /// | |
1882 | /// This is useful when you already have a collection and wants to add | |
1883 | /// the iterator items to it. | |
1884 | /// | |
1885 | /// This method is a convenience method to call [Extend::extend](trait.Extend.html), | |
1886 | /// but instead of being called on a collection, it's called on an iterator. | |
1887 | /// | |
1888 | /// # Examples | |
1889 | /// | |
1890 | /// Basic usage: | |
1891 | /// | |
1892 | /// ``` | |
1893 | /// #![feature(iter_collect_into)] | |
1894 | /// | |
1895 | /// let a = [1, 2, 3]; | |
1896 | /// let mut vec: Vec::<i32> = vec![0, 1]; | |
1897 | /// | |
1898 | /// a.iter().map(|&x| x * 2).collect_into(&mut vec); | |
1899 | /// a.iter().map(|&x| x * 10).collect_into(&mut vec); | |
1900 | /// | |
1901 | /// assert_eq!(vec![0, 1, 2, 4, 6, 10, 20, 30], vec); | |
1902 | /// ``` | |
1903 | /// | |
1904 | /// `Vec` can have a manual set capacity to avoid reallocating it: | |
1905 | /// | |
1906 | /// ``` | |
1907 | /// #![feature(iter_collect_into)] | |
1908 | /// | |
1909 | /// let a = [1, 2, 3]; | |
1910 | /// let mut vec: Vec::<i32> = Vec::with_capacity(6); | |
1911 | /// | |
1912 | /// a.iter().map(|&x| x * 2).collect_into(&mut vec); | |
1913 | /// a.iter().map(|&x| x * 10).collect_into(&mut vec); | |
1914 | /// | |
1915 | /// assert_eq!(6, vec.capacity()); | |
1916 | /// println!("{:?}", vec); | |
1917 | /// ``` | |
1918 | /// | |
1919 | /// The returned mutable reference can be used to continue the call chain: | |
1920 | /// | |
1921 | /// ``` | |
1922 | /// #![feature(iter_collect_into)] | |
1923 | /// | |
1924 | /// let a = [1, 2, 3]; | |
1925 | /// let mut vec: Vec::<i32> = Vec::with_capacity(6); | |
1926 | /// | |
1927 | /// let count = a.iter().collect_into(&mut vec).iter().count(); | |
1928 | /// | |
1929 | /// assert_eq!(count, vec.len()); | |
1930 | /// println!("Vec len is {}", count); | |
1931 | /// | |
1932 | /// let count = a.iter().collect_into(&mut vec).iter().count(); | |
1933 | /// | |
1934 | /// assert_eq!(count, vec.len()); | |
1935 | /// println!("Vec len now is {}", count); | |
1936 | /// ``` | |
1937 | #[inline] | |
1938 | #[unstable(feature = "iter_collect_into", reason = "new API", issue = "94780")] | |
1939 | fn collect_into<E: Extend<Self::Item>>(self, collection: &mut E) -> &mut E | |
1940 | where | |
1941 | Self: Sized, | |
1942 | { | |
1943 | collection.extend(self); | |
1944 | collection | |
5099ac24 FG |
1945 | } |
1946 | ||
a7813a04 XL |
1947 | /// Consumes an iterator, creating two collections from it. |
1948 | /// | |
1949 | /// The predicate passed to `partition()` can return `true`, or `false`. | |
1950 | /// `partition()` returns a pair, all of the elements for which it returned | |
1951 | /// `true`, and all of the elements for which it returned `false`. | |
1952 | /// | |
416331ca XL |
1953 | /// See also [`is_partitioned()`] and [`partition_in_place()`]. |
1954 | /// | |
1b1a35ee XL |
1955 | /// [`is_partitioned()`]: Iterator::is_partitioned |
1956 | /// [`partition_in_place()`]: Iterator::partition_in_place | |
416331ca | 1957 | /// |
a7813a04 XL |
1958 | /// # Examples |
1959 | /// | |
1960 | /// Basic usage: | |
1961 | /// | |
1962 | /// ``` | |
1963 | /// let a = [1, 2, 3]; | |
1964 | /// | |
5e7ed085 FG |
1965 | /// let (even, odd): (Vec<_>, Vec<_>) = a |
1966 | /// .into_iter() | |
1967 | /// .partition(|n| n % 2 == 0); | |
a7813a04 XL |
1968 | /// |
1969 | /// assert_eq!(even, vec![2]); | |
1970 | /// assert_eq!(odd, vec![1, 3]); | |
1971 | /// ``` | |
1972 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
1973 | fn partition<B, F>(self, f: F) -> (B, B) |
1974 | where | |
a7813a04 XL |
1975 | Self: Sized, |
1976 | B: Default + Extend<Self::Item>, | |
dfeec247 | 1977 | F: FnMut(&Self::Item) -> bool, |
a7813a04 | 1978 | { |
e1599b0c XL |
1979 | #[inline] |
1980 | fn extend<'a, T, B: Extend<T>>( | |
1981 | mut f: impl FnMut(&T) -> bool + 'a, | |
1982 | left: &'a mut B, | |
1983 | right: &'a mut B, | |
f9f354fc XL |
1984 | ) -> impl FnMut((), T) + 'a { |
1985 | move |(), x| { | |
e1599b0c | 1986 | if f(&x) { |
f9f354fc | 1987 | left.extend_one(x); |
e1599b0c | 1988 | } else { |
f9f354fc | 1989 | right.extend_one(x); |
e1599b0c XL |
1990 | } |
1991 | } | |
1992 | } | |
1993 | ||
a7813a04 XL |
1994 | let mut left: B = Default::default(); |
1995 | let mut right: B = Default::default(); | |
1996 | ||
f9f354fc | 1997 | self.fold((), extend(f, &mut left, &mut right)); |
a7813a04 XL |
1998 | |
1999 | (left, right) | |
2000 | } | |
2001 | ||
60c5eb7d | 2002 | /// Reorders the elements of this iterator *in-place* according to the given predicate, |
416331ca XL |
2003 | /// such that all those that return `true` precede all those that return `false`. |
2004 | /// Returns the number of `true` elements found. | |
2005 | /// | |
2006 | /// The relative order of partitioned items is not maintained. | |
2007 | /// | |
17df50a5 | 2008 | /// # Current implementation |
c295e0f8 | 2009 | /// |
17df50a5 XL |
2010 | /// Current algorithms tries finding the first element for which the predicate evaluates |
2011 | /// to false, and the last element for which it evaluates to true and repeatedly swaps them. | |
2012 | /// | |
c295e0f8 | 2013 | /// Time complexity: *O*(*n*) |
17df50a5 | 2014 | /// |
416331ca XL |
2015 | /// See also [`is_partitioned()`] and [`partition()`]. |
2016 | /// | |
1b1a35ee XL |
2017 | /// [`is_partitioned()`]: Iterator::is_partitioned |
2018 | /// [`partition()`]: Iterator::partition | |
416331ca XL |
2019 | /// |
2020 | /// # Examples | |
2021 | /// | |
2022 | /// ``` | |
2023 | /// #![feature(iter_partition_in_place)] | |
2024 | /// | |
2025 | /// let mut a = [1, 2, 3, 4, 5, 6, 7]; | |
2026 | /// | |
2027 | /// // Partition in-place between evens and odds | |
2028 | /// let i = a.iter_mut().partition_in_place(|&n| n % 2 == 0); | |
2029 | /// | |
2030 | /// assert_eq!(i, 3); | |
2031 | /// assert!(a[..i].iter().all(|&n| n % 2 == 0)); // evens | |
2032 | /// assert!(a[i..].iter().all(|&n| n % 2 == 1)); // odds | |
2033 | /// ``` | |
2034 | #[unstable(feature = "iter_partition_in_place", reason = "new API", issue = "62543")] | |
2035 | fn partition_in_place<'a, T: 'a, P>(mut self, ref mut predicate: P) -> usize | |
2036 | where | |
2037 | Self: Sized + DoubleEndedIterator<Item = &'a mut T>, | |
2038 | P: FnMut(&T) -> bool, | |
2039 | { | |
2040 | // FIXME: should we worry about the count overflowing? The only way to have more than | |
2041 | // `usize::MAX` mutable references is with ZSTs, which aren't useful to partition... | |
2042 | ||
2043 | // These closure "factory" functions exist to avoid genericity in `Self`. | |
2044 | ||
2045 | #[inline] | |
2046 | fn is_false<'a, T>( | |
2047 | predicate: &'a mut impl FnMut(&T) -> bool, | |
2048 | true_count: &'a mut usize, | |
2049 | ) -> impl FnMut(&&mut T) -> bool + 'a { | |
2050 | move |x| { | |
2051 | let p = predicate(&**x); | |
2052 | *true_count += p as usize; | |
2053 | !p | |
2054 | } | |
2055 | } | |
2056 | ||
2057 | #[inline] | |
dfeec247 | 2058 | fn is_true<T>(predicate: &mut impl FnMut(&T) -> bool) -> impl FnMut(&&mut T) -> bool + '_ { |
416331ca XL |
2059 | move |x| predicate(&**x) |
2060 | } | |
2061 | ||
2062 | // Repeatedly find the first `false` and swap it with the last `true`. | |
2063 | let mut true_count = 0; | |
2064 | while let Some(head) = self.find(is_false(predicate, &mut true_count)) { | |
2065 | if let Some(tail) = self.rfind(is_true(predicate)) { | |
2066 | crate::mem::swap(head, tail); | |
2067 | true_count += 1; | |
2068 | } else { | |
2069 | break; | |
2070 | } | |
2071 | } | |
2072 | true_count | |
2073 | } | |
2074 | ||
2075 | /// Checks if the elements of this iterator are partitioned according to the given predicate, | |
2076 | /// such that all those that return `true` precede all those that return `false`. | |
2077 | /// | |
2078 | /// See also [`partition()`] and [`partition_in_place()`]. | |
2079 | /// | |
1b1a35ee XL |
2080 | /// [`partition()`]: Iterator::partition |
2081 | /// [`partition_in_place()`]: Iterator::partition_in_place | |
416331ca XL |
2082 | /// |
2083 | /// # Examples | |
2084 | /// | |
2085 | /// ``` | |
2086 | /// #![feature(iter_is_partitioned)] | |
2087 | /// | |
2088 | /// assert!("Iterator".chars().is_partitioned(char::is_uppercase)); | |
2089 | /// assert!(!"IntoIterator".chars().is_partitioned(char::is_uppercase)); | |
2090 | /// ``` | |
2091 | #[unstable(feature = "iter_is_partitioned", reason = "new API", issue = "62544")] | |
2092 | fn is_partitioned<P>(mut self, mut predicate: P) -> bool | |
2093 | where | |
2094 | Self: Sized, | |
2095 | P: FnMut(Self::Item) -> bool, | |
2096 | { | |
2097 | // Either all items test `true`, or the first clause stops at `false` | |
2098 | // and we check that there are no more `true` items after that. | |
2099 | self.all(&mut predicate) || !self.any(predicate) | |
2100 | } | |
2101 | ||
abe05a73 XL |
2102 | /// An iterator method that applies a function as long as it returns |
2103 | /// successfully, producing a single, final value. | |
2104 | /// | |
2105 | /// `try_fold()` takes two arguments: an initial value, and a closure with | |
2106 | /// two arguments: an 'accumulator', and an element. The closure either | |
2107 | /// returns successfully, with the value that the accumulator should have | |
2108 | /// for the next iteration, or it returns failure, with an error value that | |
2109 | /// is propagated back to the caller immediately (short-circuiting). | |
2110 | /// | |
2111 | /// The initial value is the value the accumulator will have on the first | |
9fa01778 | 2112 | /// call. If applying the closure succeeded against every element of the |
abe05a73 XL |
2113 | /// iterator, `try_fold()` returns the final accumulator as success. |
2114 | /// | |
2115 | /// Folding is useful whenever you have a collection of something, and want | |
2116 | /// to produce a single value from it. | |
2117 | /// | |
2118 | /// # Note to Implementors | |
2119 | /// | |
f9f354fc | 2120 | /// Several of the other (forward) methods have default implementations in |
abe05a73 XL |
2121 | /// terms of this one, so try to implement this explicitly if it can |
2122 | /// do something better than the default `for` loop implementation. | |
2123 | /// | |
2124 | /// In particular, try to have this call `try_fold()` on the internal parts | |
9fa01778 | 2125 | /// from which this iterator is composed. If multiple calls are needed, |
0531ce1d XL |
2126 | /// the `?` operator may be convenient for chaining the accumulator value |
2127 | /// along, but beware any invariants that need to be upheld before those | |
9fa01778 | 2128 | /// early returns. This is a `&mut self` method, so iteration needs to be |
abe05a73 XL |
2129 | /// resumable after hitting an error here. |
2130 | /// | |
2131 | /// # Examples | |
2132 | /// | |
2133 | /// Basic usage: | |
2134 | /// | |
2135 | /// ``` | |
abe05a73 XL |
2136 | /// let a = [1, 2, 3]; |
2137 | /// | |
2138 | /// // the checked sum of all of the elements of the array | |
0531ce1d | 2139 | /// let sum = a.iter().try_fold(0i8, |acc, &x| acc.checked_add(x)); |
abe05a73 XL |
2140 | /// |
2141 | /// assert_eq!(sum, Some(6)); | |
2142 | /// ``` | |
2143 | /// | |
2144 | /// Short-circuiting: | |
2145 | /// | |
2146 | /// ``` | |
abe05a73 XL |
2147 | /// let a = [10, 20, 30, 100, 40, 50]; |
2148 | /// let mut it = a.iter(); | |
2149 | /// | |
2150 | /// // This sum overflows when adding the 100 element | |
2151 | /// let sum = it.try_fold(0i8, |acc, &x| acc.checked_add(x)); | |
2152 | /// assert_eq!(sum, None); | |
2153 | /// | |
2154 | /// // Because it short-circuited, the remaining elements are still | |
2155 | /// // available through the iterator. | |
2156 | /// assert_eq!(it.len(), 2); | |
2157 | /// assert_eq!(it.next(), Some(&40)); | |
2158 | /// ``` | |
136023e0 | 2159 | /// |
94222f64 XL |
2160 | /// While you cannot `break` from a closure, the [`ControlFlow`] type allows |
2161 | /// a similar idea: | |
136023e0 XL |
2162 | /// |
2163 | /// ``` | |
2164 | /// use std::ops::ControlFlow; | |
2165 | /// | |
2166 | /// let triangular = (1..30).try_fold(0_i8, |prev, x| { | |
2167 | /// if let Some(next) = prev.checked_add(x) { | |
2168 | /// ControlFlow::Continue(next) | |
2169 | /// } else { | |
2170 | /// ControlFlow::Break(prev) | |
2171 | /// } | |
2172 | /// }); | |
2173 | /// assert_eq!(triangular, ControlFlow::Break(120)); | |
2174 | /// | |
2175 | /// let triangular = (1..30).try_fold(0_u64, |prev, x| { | |
2176 | /// if let Some(next) = prev.checked_add(x) { | |
2177 | /// ControlFlow::Continue(next) | |
2178 | /// } else { | |
2179 | /// ControlFlow::Break(prev) | |
2180 | /// } | |
2181 | /// }); | |
2182 | /// assert_eq!(triangular, ControlFlow::Continue(435)); | |
2183 | /// ``` | |
abe05a73 | 2184 | #[inline] |
83c7162d | 2185 | #[stable(feature = "iterator_try_fold", since = "1.27.0")] |
dfeec247 XL |
2186 | fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R |
2187 | where | |
2188 | Self: Sized, | |
2189 | F: FnMut(B, Self::Item) -> R, | |
17df50a5 | 2190 | R: Try<Output = B>, |
abe05a73 XL |
2191 | { |
2192 | let mut accum = init; | |
2193 | while let Some(x) = self.next() { | |
2194 | accum = f(accum, x)?; | |
2195 | } | |
29967ef6 | 2196 | try { accum } |
abe05a73 XL |
2197 | } |
2198 | ||
0531ce1d XL |
2199 | /// An iterator method that applies a fallible function to each item in the |
2200 | /// iterator, stopping at the first error and returning that error. | |
2201 | /// | |
2202 | /// This can also be thought of as the fallible form of [`for_each()`] | |
2203 | /// or as the stateless version of [`try_fold()`]. | |
2204 | /// | |
1b1a35ee XL |
2205 | /// [`for_each()`]: Iterator::for_each |
2206 | /// [`try_fold()`]: Iterator::try_fold | |
0531ce1d XL |
2207 | /// |
2208 | /// # Examples | |
2209 | /// | |
2210 | /// ``` | |
0531ce1d XL |
2211 | /// use std::fs::rename; |
2212 | /// use std::io::{stdout, Write}; | |
2213 | /// use std::path::Path; | |
2214 | /// | |
2215 | /// let data = ["no_tea.txt", "stale_bread.json", "torrential_rain.png"]; | |
2216 | /// | |
5e7ed085 | 2217 | /// let res = data.iter().try_for_each(|x| writeln!(stdout(), "{x}")); |
0531ce1d XL |
2218 | /// assert!(res.is_ok()); |
2219 | /// | |
2220 | /// let mut it = data.iter().cloned(); | |
2221 | /// let res = it.try_for_each(|x| rename(x, Path::new(x).with_extension("old"))); | |
2222 | /// assert!(res.is_err()); | |
2223 | /// // It short-circuited, so the remaining items are still in the iterator: | |
2224 | /// assert_eq!(it.next(), Some("stale_bread.json")); | |
2225 | /// ``` | |
136023e0 | 2226 | /// |
94222f64 XL |
2227 | /// The [`ControlFlow`] type can be used with this method for the situations |
2228 | /// in which you'd use `break` and `continue` in a normal loop: | |
136023e0 XL |
2229 | /// |
2230 | /// ``` | |
2231 | /// use std::ops::ControlFlow; | |
2232 | /// | |
2233 | /// let r = (2..100).try_for_each(|x| { | |
2234 | /// if 323 % x == 0 { | |
2235 | /// return ControlFlow::Break(x) | |
2236 | /// } | |
2237 | /// | |
2238 | /// ControlFlow::Continue(()) | |
2239 | /// }); | |
2240 | /// assert_eq!(r, ControlFlow::Break(17)); | |
2241 | /// ``` | |
0531ce1d | 2242 | #[inline] |
83c7162d | 2243 | #[stable(feature = "iterator_try_fold", since = "1.27.0")] |
dfeec247 XL |
2244 | fn try_for_each<F, R>(&mut self, f: F) -> R |
2245 | where | |
2246 | Self: Sized, | |
2247 | F: FnMut(Self::Item) -> R, | |
17df50a5 | 2248 | R: Try<Output = ()>, |
0531ce1d | 2249 | { |
e1599b0c XL |
2250 | #[inline] |
2251 | fn call<T, R>(mut f: impl FnMut(T) -> R) -> impl FnMut((), T) -> R { | |
2252 | move |(), x| f(x) | |
2253 | } | |
2254 | ||
2255 | self.try_fold((), call(f)) | |
0531ce1d XL |
2256 | } |
2257 | ||
5869c6ff XL |
2258 | /// Folds every element into an accumulator by applying an operation, |
2259 | /// returning the final result. | |
a7813a04 XL |
2260 | /// |
2261 | /// `fold()` takes two arguments: an initial value, and a closure with two | |
2262 | /// arguments: an 'accumulator', and an element. The closure returns the value that | |
2263 | /// the accumulator should have for the next iteration. | |
2264 | /// | |
2265 | /// The initial value is the value the accumulator will have on the first | |
2266 | /// call. | |
2267 | /// | |
2268 | /// After applying this closure to every element of the iterator, `fold()` | |
2269 | /// returns the accumulator. | |
2270 | /// | |
2271 | /// This operation is sometimes called 'reduce' or 'inject'. | |
2272 | /// | |
2273 | /// Folding is useful whenever you have a collection of something, and want | |
2274 | /// to produce a single value from it. | |
2275 | /// | |
2c00a5a8 | 2276 | /// Note: `fold()`, and similar methods that traverse the entire iterator, |
94222f64 | 2277 | /// might not terminate for infinite iterators, even on traits for which a |
2c00a5a8 XL |
2278 | /// result is determinable in finite time. |
2279 | /// | |
5869c6ff XL |
2280 | /// Note: [`reduce()`] can be used to use the first element as the initial |
2281 | /// value, if the accumulator type and item type is the same. | |
2282 | /// | |
136023e0 XL |
2283 | /// Note: `fold()` combines elements in a *left-associative* fashion. For associative |
2284 | /// operators like `+`, the order the elements are combined in is not important, but for non-associative | |
2285 | /// operators like `-` the order will affect the final result. | |
2286 | /// For a *right-associative* version of `fold()`, see [`DoubleEndedIterator::rfold()`]. | |
2287 | /// | |
f9f354fc XL |
2288 | /// # Note to Implementors |
2289 | /// | |
2290 | /// Several of the other (forward) methods have default implementations in | |
2291 | /// terms of this one, so try to implement this explicitly if it can | |
2292 | /// do something better than the default `for` loop implementation. | |
2293 | /// | |
2294 | /// In particular, try to have this call `fold()` on the internal parts | |
2295 | /// from which this iterator is composed. | |
2296 | /// | |
a7813a04 XL |
2297 | /// # Examples |
2298 | /// | |
2299 | /// Basic usage: | |
2300 | /// | |
2301 | /// ``` | |
2302 | /// let a = [1, 2, 3]; | |
2303 | /// | |
abe05a73 | 2304 | /// // the sum of all of the elements of the array |
0531ce1d | 2305 | /// let sum = a.iter().fold(0, |acc, x| acc + x); |
a7813a04 XL |
2306 | /// |
2307 | /// assert_eq!(sum, 6); | |
2308 | /// ``` | |
2309 | /// | |
2310 | /// Let's walk through each step of the iteration here: | |
2311 | /// | |
2312 | /// | element | acc | x | result | | |
2313 | /// |---------|-----|---|--------| | |
2314 | /// | | 0 | | | | |
2315 | /// | 1 | 0 | 1 | 1 | | |
2316 | /// | 2 | 1 | 2 | 3 | | |
2317 | /// | 3 | 3 | 3 | 6 | | |
2318 | /// | |
2319 | /// And so, our final result, `6`. | |
2320 | /// | |
136023e0 XL |
2321 | /// This example demonstrates the left-associative nature of `fold()`: |
2322 | /// it builds a string, starting with an initial value | |
2323 | /// and continuing with each element from the front until the back: | |
2324 | /// | |
2325 | /// ``` | |
2326 | /// let numbers = [1, 2, 3, 4, 5]; | |
2327 | /// | |
2328 | /// let zero = "0".to_string(); | |
2329 | /// | |
2330 | /// let result = numbers.iter().fold(zero, |acc, &x| { | |
5e7ed085 | 2331 | /// format!("({acc} + {x})") |
136023e0 XL |
2332 | /// }); |
2333 | /// | |
2334 | /// assert_eq!(result, "(((((0 + 1) + 2) + 3) + 4) + 5)"); | |
2335 | /// ``` | |
a7813a04 XL |
2336 | /// It's common for people who haven't used iterators a lot to |
2337 | /// use a `for` loop with a list of things to build up a result. Those | |
2338 | /// can be turned into `fold()`s: | |
2339 | /// | |
13cf67c4 | 2340 | /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for |
476ff2be | 2341 | /// |
a7813a04 XL |
2342 | /// ``` |
2343 | /// let numbers = [1, 2, 3, 4, 5]; | |
2344 | /// | |
2345 | /// let mut result = 0; | |
2346 | /// | |
2347 | /// // for loop: | |
2348 | /// for i in &numbers { | |
2349 | /// result = result + i; | |
2350 | /// } | |
2351 | /// | |
2352 | /// // fold: | |
2353 | /// let result2 = numbers.iter().fold(0, |acc, &x| acc + x); | |
2354 | /// | |
2355 | /// // they're the same | |
2356 | /// assert_eq!(result, result2); | |
2357 | /// ``` | |
5869c6ff XL |
2358 | /// |
2359 | /// [`reduce()`]: Iterator::reduce | |
136023e0 | 2360 | #[doc(alias = "inject", alias = "foldl")] |
a7813a04 XL |
2361 | #[inline] |
2362 | #[stable(feature = "rust1", since = "1.0.0")] | |
f9f354fc | 2363 | fn fold<B, F>(mut self, init: B, mut f: F) -> B |
dfeec247 XL |
2364 | where |
2365 | Self: Sized, | |
2366 | F: FnMut(B, Self::Item) -> B, | |
a7813a04 | 2367 | { |
f9f354fc XL |
2368 | let mut accum = init; |
2369 | while let Some(x) = self.next() { | |
2370 | accum = f(accum, x); | |
e1599b0c | 2371 | } |
f9f354fc | 2372 | accum |
a7813a04 XL |
2373 | } |
2374 | ||
5869c6ff XL |
2375 | /// Reduces the elements to a single one, by repeatedly applying a reducing |
2376 | /// operation. | |
2377 | /// | |
2378 | /// If the iterator is empty, returns [`None`]; otherwise, returns the | |
2379 | /// result of the reduction. | |
2380 | /// | |
c295e0f8 | 2381 | /// The reducing function is a closure with two arguments: an 'accumulator', and an element. |
5869c6ff | 2382 | /// For iterators with at least one element, this is the same as [`fold()`] |
c295e0f8 | 2383 | /// with the first element of the iterator as the initial accumulator value, folding |
5869c6ff | 2384 | /// every subsequent element into it. |
ba9703b0 | 2385 | /// |
1b1a35ee XL |
2386 | /// [`fold()`]: Iterator::fold |
2387 | /// | |
ba9703b0 XL |
2388 | /// # Example |
2389 | /// | |
2390 | /// Find the maximum value: | |
2391 | /// | |
2392 | /// ``` | |
ba9703b0 XL |
2393 | /// fn find_max<I>(iter: I) -> Option<I::Item> |
2394 | /// where I: Iterator, | |
2395 | /// I::Item: Ord, | |
2396 | /// { | |
c295e0f8 XL |
2397 | /// iter.reduce(|accum, item| { |
2398 | /// if accum >= item { accum } else { item } | |
ba9703b0 XL |
2399 | /// }) |
2400 | /// } | |
2401 | /// let a = [10, 20, 5, -23, 0]; | |
2402 | /// let b: [u32; 0] = []; | |
2403 | /// | |
2404 | /// assert_eq!(find_max(a.iter()), Some(&20)); | |
2405 | /// assert_eq!(find_max(b.iter()), None); | |
2406 | /// ``` | |
2407 | #[inline] | |
5869c6ff XL |
2408 | #[stable(feature = "iterator_fold_self", since = "1.51.0")] |
2409 | fn reduce<F>(mut self, f: F) -> Option<Self::Item> | |
ba9703b0 XL |
2410 | where |
2411 | Self: Sized, | |
2412 | F: FnMut(Self::Item, Self::Item) -> Self::Item, | |
2413 | { | |
2414 | let first = self.next()?; | |
2415 | Some(self.fold(first, f)) | |
2416 | } | |
2417 | ||
a2a8927a XL |
2418 | /// Reduces the elements to a single one by repeatedly applying a reducing operation. If the |
2419 | /// closure returns a failure, the failure is propagated back to the caller immediately. | |
2420 | /// | |
2421 | /// The return type of this method depends on the return type of the closure. If the closure | |
2422 | /// returns `Result<Self::Item, E>`, then this function will return `Result<Option<Self::Item>, | |
2423 | /// E>`. If the closure returns `Option<Self::Item>`, then this function will return | |
2424 | /// `Option<Option<Self::Item>>`. | |
2425 | /// | |
2426 | /// When called on an empty iterator, this function will return either `Some(None)` or | |
2427 | /// `Ok(None)` depending on the type of the provided closure. | |
2428 | /// | |
2429 | /// For iterators with at least one element, this is essentially the same as calling | |
2430 | /// [`try_fold()`] with the first element of the iterator as the initial accumulator value. | |
2431 | /// | |
2432 | /// [`try_fold()`]: Iterator::try_fold | |
2433 | /// | |
2434 | /// # Examples | |
2435 | /// | |
2436 | /// Safely calculate the sum of a series of numbers: | |
2437 | /// | |
2438 | /// ``` | |
2439 | /// #![feature(iterator_try_reduce)] | |
2440 | /// | |
2441 | /// let numbers: Vec<usize> = vec![10, 20, 5, 23, 0]; | |
2442 | /// let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y)); | |
2443 | /// assert_eq!(sum, Some(Some(58))); | |
2444 | /// ``` | |
2445 | /// | |
2446 | /// Determine when a reduction short circuited: | |
2447 | /// | |
2448 | /// ``` | |
2449 | /// #![feature(iterator_try_reduce)] | |
2450 | /// | |
2451 | /// let numbers = vec![1, 2, 3, usize::MAX, 4, 5]; | |
2452 | /// let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y)); | |
2453 | /// assert_eq!(sum, None); | |
2454 | /// ``` | |
2455 | /// | |
2456 | /// Determine when a reduction was not performed because there are no elements: | |
2457 | /// | |
2458 | /// ``` | |
2459 | /// #![feature(iterator_try_reduce)] | |
2460 | /// | |
2461 | /// let numbers: Vec<usize> = Vec::new(); | |
2462 | /// let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y)); | |
2463 | /// assert_eq!(sum, Some(None)); | |
2464 | /// ``` | |
2465 | /// | |
2466 | /// Use a [`Result`] instead of an [`Option`]: | |
2467 | /// | |
2468 | /// ``` | |
2469 | /// #![feature(iterator_try_reduce)] | |
2470 | /// | |
2471 | /// let numbers = vec!["1", "2", "3", "4", "5"]; | |
2472 | /// let max: Result<Option<_>, <usize as std::str::FromStr>::Err> = | |
2473 | /// numbers.into_iter().try_reduce(|x, y| { | |
2474 | /// if x.parse::<usize>()? > y.parse::<usize>()? { Ok(x) } else { Ok(y) } | |
2475 | /// }); | |
2476 | /// assert_eq!(max, Ok(Some("5"))); | |
2477 | /// ``` | |
2478 | #[inline] | |
2479 | #[unstable(feature = "iterator_try_reduce", reason = "new API", issue = "87053")] | |
2480 | fn try_reduce<F, R>(&mut self, f: F) -> ChangeOutputType<R, Option<R::Output>> | |
2481 | where | |
2482 | Self: Sized, | |
2483 | F: FnMut(Self::Item, Self::Item) -> R, | |
2484 | R: Try<Output = Self::Item>, | |
2485 | R::Residual: Residual<Option<Self::Item>>, | |
2486 | { | |
2487 | let first = match self.next() { | |
2488 | Some(i) => i, | |
2489 | None => return Try::from_output(None), | |
2490 | }; | |
2491 | ||
2492 | match self.try_fold(first, f).branch() { | |
2493 | ControlFlow::Break(r) => FromResidual::from_residual(r), | |
2494 | ControlFlow::Continue(i) => Try::from_output(Some(i)), | |
2495 | } | |
2496 | } | |
2497 | ||
a7813a04 XL |
2498 | /// Tests if every element of the iterator matches a predicate. |
2499 | /// | |
2500 | /// `all()` takes a closure that returns `true` or `false`. It applies | |
2501 | /// this closure to each element of the iterator, and if they all return | |
2502 | /// `true`, then so does `all()`. If any of them return `false`, it | |
2503 | /// returns `false`. | |
2504 | /// | |
2505 | /// `all()` is short-circuiting; in other words, it will stop processing | |
2506 | /// as soon as it finds a `false`, given that no matter what else happens, | |
2507 | /// the result will also be `false`. | |
2508 | /// | |
2509 | /// An empty iterator returns `true`. | |
2510 | /// | |
2511 | /// # Examples | |
2512 | /// | |
2513 | /// Basic usage: | |
2514 | /// | |
2515 | /// ``` | |
2516 | /// let a = [1, 2, 3]; | |
2517 | /// | |
2518 | /// assert!(a.iter().all(|&x| x > 0)); | |
2519 | /// | |
2520 | /// assert!(!a.iter().all(|&x| x > 2)); | |
2521 | /// ``` | |
2522 | /// | |
2523 | /// Stopping at the first `false`: | |
2524 | /// | |
2525 | /// ``` | |
2526 | /// let a = [1, 2, 3]; | |
2527 | /// | |
2528 | /// let mut iter = a.iter(); | |
2529 | /// | |
2530 | /// assert!(!iter.all(|&x| x != 2)); | |
2531 | /// | |
2532 | /// // we can still use `iter`, as there are more elements. | |
2533 | /// assert_eq!(iter.next(), Some(&3)); | |
2534 | /// ``` | |
2535 | #[inline] | |
2536 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
2537 | fn all<F>(&mut self, f: F) -> bool |
2538 | where | |
2539 | Self: Sized, | |
2540 | F: FnMut(Self::Item) -> bool, | |
a7813a04 | 2541 | { |
e1599b0c | 2542 | #[inline] |
2a314972 | 2543 | fn check<T>(mut f: impl FnMut(T) -> bool) -> impl FnMut((), T) -> ControlFlow<()> { |
e74abb32 | 2544 | move |(), x| { |
1b1a35ee | 2545 | if f(x) { ControlFlow::CONTINUE } else { ControlFlow::BREAK } |
e1599b0c XL |
2546 | } |
2547 | } | |
1b1a35ee | 2548 | self.try_fold((), check(f)) == ControlFlow::CONTINUE |
a7813a04 XL |
2549 | } |
2550 | ||
2551 | /// Tests if any element of the iterator matches a predicate. | |
2552 | /// | |
2553 | /// `any()` takes a closure that returns `true` or `false`. It applies | |
2554 | /// this closure to each element of the iterator, and if any of them return | |
2555 | /// `true`, then so does `any()`. If they all return `false`, it | |
2556 | /// returns `false`. | |
2557 | /// | |
2558 | /// `any()` is short-circuiting; in other words, it will stop processing | |
2559 | /// as soon as it finds a `true`, given that no matter what else happens, | |
2560 | /// the result will also be `true`. | |
2561 | /// | |
2562 | /// An empty iterator returns `false`. | |
2563 | /// | |
2564 | /// # Examples | |
2565 | /// | |
2566 | /// Basic usage: | |
2567 | /// | |
2568 | /// ``` | |
2569 | /// let a = [1, 2, 3]; | |
2570 | /// | |
2571 | /// assert!(a.iter().any(|&x| x > 0)); | |
2572 | /// | |
2573 | /// assert!(!a.iter().any(|&x| x > 5)); | |
2574 | /// ``` | |
2575 | /// | |
2576 | /// Stopping at the first `true`: | |
2577 | /// | |
2578 | /// ``` | |
2579 | /// let a = [1, 2, 3]; | |
2580 | /// | |
2581 | /// let mut iter = a.iter(); | |
2582 | /// | |
2583 | /// assert!(iter.any(|&x| x != 2)); | |
2584 | /// | |
2585 | /// // we can still use `iter`, as there are more elements. | |
2586 | /// assert_eq!(iter.next(), Some(&2)); | |
2587 | /// ``` | |
2588 | #[inline] | |
2589 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
2590 | fn any<F>(&mut self, f: F) -> bool |
2591 | where | |
a7813a04 | 2592 | Self: Sized, |
dfeec247 | 2593 | F: FnMut(Self::Item) -> bool, |
a7813a04 | 2594 | { |
e1599b0c | 2595 | #[inline] |
2a314972 | 2596 | fn check<T>(mut f: impl FnMut(T) -> bool) -> impl FnMut((), T) -> ControlFlow<()> { |
e74abb32 | 2597 | move |(), x| { |
1b1a35ee | 2598 | if f(x) { ControlFlow::BREAK } else { ControlFlow::CONTINUE } |
e1599b0c XL |
2599 | } |
2600 | } | |
2601 | ||
1b1a35ee | 2602 | self.try_fold((), check(f)) == ControlFlow::BREAK |
a7813a04 XL |
2603 | } |
2604 | ||
2605 | /// Searches for an element of an iterator that satisfies a predicate. | |
2606 | /// | |
2607 | /// `find()` takes a closure that returns `true` or `false`. It applies | |
2608 | /// this closure to each element of the iterator, and if any of them return | |
476ff2be SL |
2609 | /// `true`, then `find()` returns [`Some(element)`]. If they all return |
2610 | /// `false`, it returns [`None`]. | |
a7813a04 XL |
2611 | /// |
2612 | /// `find()` is short-circuiting; in other words, it will stop processing | |
2613 | /// as soon as the closure returns `true`. | |
2614 | /// | |
2615 | /// Because `find()` takes a reference, and many iterators iterate over | |
2616 | /// references, this leads to a possibly confusing situation where the | |
2617 | /// argument is a double reference. You can see this effect in the | |
2618 | /// examples below, with `&&x`. | |
2619 | /// | |
3dfed10e | 2620 | /// [`Some(element)`]: Some |
476ff2be | 2621 | /// |
a7813a04 XL |
2622 | /// # Examples |
2623 | /// | |
2624 | /// Basic usage: | |
2625 | /// | |
2626 | /// ``` | |
2627 | /// let a = [1, 2, 3]; | |
2628 | /// | |
2629 | /// assert_eq!(a.iter().find(|&&x| x == 2), Some(&2)); | |
2630 | /// | |
2631 | /// assert_eq!(a.iter().find(|&&x| x == 5), None); | |
2632 | /// ``` | |
2633 | /// | |
2634 | /// Stopping at the first `true`: | |
2635 | /// | |
2636 | /// ``` | |
2637 | /// let a = [1, 2, 3]; | |
2638 | /// | |
2639 | /// let mut iter = a.iter(); | |
2640 | /// | |
2641 | /// assert_eq!(iter.find(|&&x| x == 2), Some(&2)); | |
2642 | /// | |
2643 | /// // we can still use `iter`, as there are more elements. | |
2644 | /// assert_eq!(iter.next(), Some(&3)); | |
2645 | /// ``` | |
74b04a01 XL |
2646 | /// |
2647 | /// Note that `iter.find(f)` is equivalent to `iter.filter(f).next()`. | |
a7813a04 XL |
2648 | #[inline] |
2649 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
2650 | fn find<P>(&mut self, predicate: P) -> Option<Self::Item> |
2651 | where | |
a7813a04 XL |
2652 | Self: Sized, |
2653 | P: FnMut(&Self::Item) -> bool, | |
2654 | { | |
e1599b0c | 2655 | #[inline] |
2a314972 | 2656 | fn check<T>(mut predicate: impl FnMut(&T) -> bool) -> impl FnMut((), T) -> ControlFlow<T> { |
e74abb32 | 2657 | move |(), x| { |
1b1a35ee | 2658 | if predicate(&x) { ControlFlow::Break(x) } else { ControlFlow::CONTINUE } |
e1599b0c XL |
2659 | } |
2660 | } | |
2661 | ||
e74abb32 | 2662 | self.try_fold((), check(predicate)).break_value() |
a7813a04 XL |
2663 | } |
2664 | ||
83c7162d XL |
2665 | /// Applies function to the elements of iterator and returns |
2666 | /// the first non-none result. | |
2667 | /// | |
2668 | /// `iter.find_map(f)` is equivalent to `iter.filter_map(f).next()`. | |
2669 | /// | |
83c7162d XL |
2670 | /// # Examples |
2671 | /// | |
2672 | /// ``` | |
83c7162d XL |
2673 | /// let a = ["lol", "NaN", "2", "5"]; |
2674 | /// | |
a1dfa0c6 | 2675 | /// let first_number = a.iter().find_map(|s| s.parse().ok()); |
83c7162d XL |
2676 | /// |
2677 | /// assert_eq!(first_number, Some(2)); | |
2678 | /// ``` | |
2679 | #[inline] | |
b7449926 | 2680 | #[stable(feature = "iterator_find_map", since = "1.30.0")] |
dfeec247 XL |
2681 | fn find_map<B, F>(&mut self, f: F) -> Option<B> |
2682 | where | |
83c7162d XL |
2683 | Self: Sized, |
2684 | F: FnMut(Self::Item) -> Option<B>, | |
2685 | { | |
e1599b0c | 2686 | #[inline] |
2a314972 | 2687 | fn check<T, B>(mut f: impl FnMut(T) -> Option<B>) -> impl FnMut((), T) -> ControlFlow<B> { |
e74abb32 | 2688 | move |(), x| match f(x) { |
1b1a35ee XL |
2689 | Some(x) => ControlFlow::Break(x), |
2690 | None => ControlFlow::CONTINUE, | |
83c7162d | 2691 | } |
e1599b0c XL |
2692 | } |
2693 | ||
e74abb32 | 2694 | self.try_fold((), check(f)).break_value() |
83c7162d XL |
2695 | } |
2696 | ||
dfeec247 | 2697 | /// Applies function to the elements of iterator and returns |
f035d41b | 2698 | /// the first true result or the first error. |
dfeec247 | 2699 | /// |
a2a8927a XL |
2700 | /// The return type of this method depends on the return type of the closure. |
2701 | /// If you return `Result<bool, E>` from the closure, you'll get a `Result<Option<Self::Item>; E>`. | |
2702 | /// If you return `Option<bool>` from the closure, you'll get an `Option<Option<Self::Item>>`. | |
2703 | /// | |
dfeec247 XL |
2704 | /// # Examples |
2705 | /// | |
2706 | /// ``` | |
2707 | /// #![feature(try_find)] | |
2708 | /// | |
2709 | /// let a = ["1", "2", "lol", "NaN", "5"]; | |
2710 | /// | |
2711 | /// let is_my_num = |s: &str, search: i32| -> Result<bool, std::num::ParseIntError> { | |
2712 | /// Ok(s.parse::<i32>()? == search) | |
2713 | /// }; | |
2714 | /// | |
2715 | /// let result = a.iter().try_find(|&&s| is_my_num(s, 2)); | |
2716 | /// assert_eq!(result, Ok(Some(&"2"))); | |
2717 | /// | |
2718 | /// let result = a.iter().try_find(|&&s| is_my_num(s, 5)); | |
2719 | /// assert!(result.is_err()); | |
2720 | /// ``` | |
a2a8927a XL |
2721 | /// |
2722 | /// This also supports other types which implement `Try`, not just `Result`. | |
2723 | /// ``` | |
2724 | /// #![feature(try_find)] | |
2725 | /// | |
2726 | /// use std::num::NonZeroU32; | |
2727 | /// let a = [3, 5, 7, 4, 9, 0, 11]; | |
2728 | /// let result = a.iter().try_find(|&&x| NonZeroU32::new(x).map(|y| y.is_power_of_two())); | |
2729 | /// assert_eq!(result, Some(Some(&4))); | |
2730 | /// let result = a.iter().take(3).try_find(|&&x| NonZeroU32::new(x).map(|y| y.is_power_of_two())); | |
2731 | /// assert_eq!(result, Some(None)); | |
2732 | /// let result = a.iter().rev().try_find(|&&x| NonZeroU32::new(x).map(|y| y.is_power_of_two())); | |
2733 | /// assert_eq!(result, None); | |
2734 | /// ``` | |
dfeec247 XL |
2735 | #[inline] |
2736 | #[unstable(feature = "try_find", reason = "new API", issue = "63178")] | |
a2a8927a | 2737 | fn try_find<F, R>(&mut self, f: F) -> ChangeOutputType<R, Option<Self::Item>> |
17df50a5 XL |
2738 | where |
2739 | Self: Sized, | |
2740 | F: FnMut(&Self::Item) -> R, | |
2741 | R: Try<Output = bool>, | |
a2a8927a | 2742 | R::Residual: Residual<Option<Self::Item>>, |
17df50a5 XL |
2743 | { |
2744 | #[inline] | |
a2a8927a XL |
2745 | fn check<I, V, R>( |
2746 | mut f: impl FnMut(&I) -> V, | |
2747 | ) -> impl FnMut((), I) -> ControlFlow<R::TryType> | |
17df50a5 | 2748 | where |
a2a8927a XL |
2749 | V: Try<Output = bool, Residual = R>, |
2750 | R: Residual<Option<I>>, | |
17df50a5 XL |
2751 | { |
2752 | move |(), x| match f(&x).branch() { | |
2753 | ControlFlow::Continue(false) => ControlFlow::CONTINUE, | |
a2a8927a XL |
2754 | ControlFlow::Continue(true) => ControlFlow::Break(Try::from_output(Some(x))), |
2755 | ControlFlow::Break(r) => ControlFlow::Break(FromResidual::from_residual(r)), | |
17df50a5 XL |
2756 | } |
2757 | } | |
2758 | ||
a2a8927a XL |
2759 | match self.try_fold((), check(f)) { |
2760 | ControlFlow::Break(x) => x, | |
2761 | ControlFlow::Continue(()) => Try::from_output(None), | |
2762 | } | |
17df50a5 XL |
2763 | } |
2764 | ||
a7813a04 XL |
2765 | /// Searches for an element in an iterator, returning its index. |
2766 | /// | |
2767 | /// `position()` takes a closure that returns `true` or `false`. It applies | |
2768 | /// this closure to each element of the iterator, and if one of them | |
476ff2be SL |
2769 | /// returns `true`, then `position()` returns [`Some(index)`]. If all of |
2770 | /// them return `false`, it returns [`None`]. | |
a7813a04 XL |
2771 | /// |
2772 | /// `position()` is short-circuiting; in other words, it will stop | |
2773 | /// processing as soon as it finds a `true`. | |
2774 | /// | |
2775 | /// # Overflow Behavior | |
2776 | /// | |
2777 | /// The method does no guarding against overflows, so if there are more | |
476ff2be | 2778 | /// than [`usize::MAX`] non-matching elements, it either produces the wrong |
a7813a04 XL |
2779 | /// result or panics. If debug assertions are enabled, a panic is |
2780 | /// guaranteed. | |
2781 | /// | |
2782 | /// # Panics | |
2783 | /// | |
2784 | /// This function might panic if the iterator has more than `usize::MAX` | |
2785 | /// non-matching elements. | |
2786 | /// | |
3dfed10e | 2787 | /// [`Some(index)`]: Some |
476ff2be | 2788 | /// |
a7813a04 XL |
2789 | /// # Examples |
2790 | /// | |
2791 | /// Basic usage: | |
2792 | /// | |
2793 | /// ``` | |
2794 | /// let a = [1, 2, 3]; | |
2795 | /// | |
2796 | /// assert_eq!(a.iter().position(|&x| x == 2), Some(1)); | |
2797 | /// | |
2798 | /// assert_eq!(a.iter().position(|&x| x == 5), None); | |
2799 | /// ``` | |
2800 | /// | |
2801 | /// Stopping at the first `true`: | |
2802 | /// | |
2803 | /// ``` | |
cc61c64b | 2804 | /// let a = [1, 2, 3, 4]; |
a7813a04 XL |
2805 | /// |
2806 | /// let mut iter = a.iter(); | |
2807 | /// | |
cc61c64b | 2808 | /// assert_eq!(iter.position(|&x| x >= 2), Some(1)); |
a7813a04 XL |
2809 | /// |
2810 | /// // we can still use `iter`, as there are more elements. | |
2811 | /// assert_eq!(iter.next(), Some(&3)); | |
cc61c64b XL |
2812 | /// |
2813 | /// // The returned index depends on iterator state | |
2814 | /// assert_eq!(iter.position(|&x| x == 4), Some(0)); | |
2815 | /// | |
a7813a04 XL |
2816 | /// ``` |
2817 | #[inline] | |
2818 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
2819 | fn position<P>(&mut self, predicate: P) -> Option<usize> |
2820 | where | |
a7813a04 XL |
2821 | Self: Sized, |
2822 | P: FnMut(Self::Item) -> bool, | |
2823 | { | |
e1599b0c XL |
2824 | #[inline] |
2825 | fn check<T>( | |
2826 | mut predicate: impl FnMut(T) -> bool, | |
1b1a35ee | 2827 | ) -> impl FnMut(usize, T) -> ControlFlow<usize, usize> { |
6a06907d | 2828 | #[rustc_inherit_overflow_checks] |
e1599b0c | 2829 | move |i, x| { |
6a06907d | 2830 | if predicate(x) { ControlFlow::Break(i) } else { ControlFlow::Continue(i + 1) } |
e1599b0c XL |
2831 | } |
2832 | } | |
2833 | ||
2834 | self.try_fold(0, check(predicate)).break_value() | |
a7813a04 XL |
2835 | } |
2836 | ||
2837 | /// Searches for an element in an iterator from the right, returning its | |
2838 | /// index. | |
2839 | /// | |
2840 | /// `rposition()` takes a closure that returns `true` or `false`. It applies | |
2841 | /// this closure to each element of the iterator, starting from the end, | |
2842 | /// and if one of them returns `true`, then `rposition()` returns | |
476ff2be | 2843 | /// [`Some(index)`]. If all of them return `false`, it returns [`None`]. |
a7813a04 XL |
2844 | /// |
2845 | /// `rposition()` is short-circuiting; in other words, it will stop | |
2846 | /// processing as soon as it finds a `true`. | |
2847 | /// | |
3dfed10e | 2848 | /// [`Some(index)`]: Some |
476ff2be | 2849 | /// |
a7813a04 XL |
2850 | /// # Examples |
2851 | /// | |
2852 | /// Basic usage: | |
2853 | /// | |
2854 | /// ``` | |
2855 | /// let a = [1, 2, 3]; | |
2856 | /// | |
2857 | /// assert_eq!(a.iter().rposition(|&x| x == 3), Some(2)); | |
2858 | /// | |
2859 | /// assert_eq!(a.iter().rposition(|&x| x == 5), None); | |
2860 | /// ``` | |
2861 | /// | |
2862 | /// Stopping at the first `true`: | |
2863 | /// | |
2864 | /// ``` | |
2865 | /// let a = [1, 2, 3]; | |
2866 | /// | |
2867 | /// let mut iter = a.iter(); | |
2868 | /// | |
2869 | /// assert_eq!(iter.rposition(|&x| x == 2), Some(1)); | |
2870 | /// | |
2871 | /// // we can still use `iter`, as there are more elements. | |
2872 | /// assert_eq!(iter.next(), Some(&1)); | |
2873 | /// ``` | |
2874 | #[inline] | |
2875 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
2876 | fn rposition<P>(&mut self, predicate: P) -> Option<usize> |
2877 | where | |
a7813a04 | 2878 | P: FnMut(Self::Item) -> bool, |
dfeec247 | 2879 | Self: Sized + ExactSizeIterator + DoubleEndedIterator, |
a7813a04 | 2880 | { |
abe05a73 XL |
2881 | // No need for an overflow check here, because `ExactSizeIterator` |
2882 | // implies that the number of elements fits into a `usize`. | |
e1599b0c XL |
2883 | #[inline] |
2884 | fn check<T>( | |
2885 | mut predicate: impl FnMut(T) -> bool, | |
1b1a35ee | 2886 | ) -> impl FnMut(usize, T) -> ControlFlow<usize, usize> { |
e1599b0c XL |
2887 | move |i, x| { |
2888 | let i = i - 1; | |
1b1a35ee | 2889 | if predicate(x) { ControlFlow::Break(i) } else { ControlFlow::Continue(i) } |
e1599b0c XL |
2890 | } |
2891 | } | |
2892 | ||
abe05a73 | 2893 | let n = self.len(); |
e1599b0c | 2894 | self.try_rfold(n, check(predicate)).break_value() |
a7813a04 XL |
2895 | } |
2896 | ||
2897 | /// Returns the maximum element of an iterator. | |
2898 | /// | |
32a655c1 | 2899 | /// If several elements are equally maximum, the last element is |
8bb4bdeb XL |
2900 | /// returned. If the iterator is empty, [`None`] is returned. |
2901 | /// | |
17df50a5 XL |
2902 | /// Note that [`f32`]/[`f64`] doesn't implement [`Ord`] due to NaN being |
2903 | /// incomparable. You can work around this by using [`Iterator::reduce`]: | |
2904 | /// ``` | |
2905 | /// assert_eq!( | |
5099ac24 | 2906 | /// [2.4, f32::NAN, 1.3] |
17df50a5 XL |
2907 | /// .into_iter() |
2908 | /// .reduce(f32::max) | |
2909 | /// .unwrap(), | |
2910 | /// 2.4 | |
2911 | /// ); | |
2912 | /// ``` | |
2913 | /// | |
a7813a04 XL |
2914 | /// # Examples |
2915 | /// | |
2916 | /// Basic usage: | |
2917 | /// | |
2918 | /// ``` | |
2919 | /// let a = [1, 2, 3]; | |
8bb4bdeb | 2920 | /// let b: Vec<u32> = Vec::new(); |
a7813a04 XL |
2921 | /// |
2922 | /// assert_eq!(a.iter().max(), Some(&3)); | |
8bb4bdeb | 2923 | /// assert_eq!(b.iter().max(), None); |
a7813a04 XL |
2924 | /// ``` |
2925 | #[inline] | |
2926 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
2927 | fn max(self) -> Option<Self::Item> |
2928 | where | |
2929 | Self: Sized, | |
2930 | Self::Item: Ord, | |
a7813a04 | 2931 | { |
532ac7d7 | 2932 | self.max_by(Ord::cmp) |
a7813a04 XL |
2933 | } |
2934 | ||
2935 | /// Returns the minimum element of an iterator. | |
2936 | /// | |
17df50a5 XL |
2937 | /// If several elements are equally minimum, the first element is returned. |
2938 | /// If the iterator is empty, [`None`] is returned. | |
2939 | /// | |
2940 | /// Note that [`f32`]/[`f64`] doesn't implement [`Ord`] due to NaN being | |
2941 | /// incomparable. You can work around this by using [`Iterator::reduce`]: | |
2942 | /// ``` | |
2943 | /// assert_eq!( | |
5099ac24 | 2944 | /// [2.4, f32::NAN, 1.3] |
17df50a5 XL |
2945 | /// .into_iter() |
2946 | /// .reduce(f32::min) | |
2947 | /// .unwrap(), | |
2948 | /// 1.3 | |
2949 | /// ); | |
2950 | /// ``` | |
8bb4bdeb | 2951 | /// |
a7813a04 XL |
2952 | /// # Examples |
2953 | /// | |
2954 | /// Basic usage: | |
2955 | /// | |
2956 | /// ``` | |
2957 | /// let a = [1, 2, 3]; | |
8bb4bdeb | 2958 | /// let b: Vec<u32> = Vec::new(); |
a7813a04 XL |
2959 | /// |
2960 | /// assert_eq!(a.iter().min(), Some(&1)); | |
8bb4bdeb | 2961 | /// assert_eq!(b.iter().min(), None); |
a7813a04 XL |
2962 | /// ``` |
2963 | #[inline] | |
2964 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
2965 | fn min(self) -> Option<Self::Item> |
2966 | where | |
2967 | Self: Sized, | |
2968 | Self::Item: Ord, | |
a7813a04 | 2969 | { |
532ac7d7 | 2970 | self.min_by(Ord::cmp) |
a7813a04 XL |
2971 | } |
2972 | ||
2973 | /// Returns the element that gives the maximum value from the | |
2974 | /// specified function. | |
2975 | /// | |
32a655c1 | 2976 | /// If several elements are equally maximum, the last element is |
8bb4bdeb XL |
2977 | /// returned. If the iterator is empty, [`None`] is returned. |
2978 | /// | |
a7813a04 XL |
2979 | /// # Examples |
2980 | /// | |
2981 | /// ``` | |
2982 | /// let a = [-3_i32, 0, 1, 5, -10]; | |
2983 | /// assert_eq!(*a.iter().max_by_key(|x| x.abs()).unwrap(), -10); | |
2984 | /// ``` | |
2985 | #[inline] | |
2986 | #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] | |
e1599b0c | 2987 | fn max_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item> |
dfeec247 XL |
2988 | where |
2989 | Self: Sized, | |
2990 | F: FnMut(&Self::Item) -> B, | |
a7813a04 | 2991 | { |
e1599b0c XL |
2992 | #[inline] |
2993 | fn key<T, B>(mut f: impl FnMut(&T) -> B) -> impl FnMut(T) -> (B, T) { | |
2994 | move |x| (f(&x), x) | |
2995 | } | |
2996 | ||
2997 | #[inline] | |
2998 | fn compare<T, B: Ord>((x_p, _): &(B, T), (y_p, _): &(B, T)) -> Ordering { | |
2999 | x_p.cmp(y_p) | |
3000 | } | |
3001 | ||
3002 | let (_, x) = self.map(key(f)).max_by(compare)?; | |
3003 | Some(x) | |
a7813a04 XL |
3004 | } |
3005 | ||
9e0c209e SL |
3006 | /// Returns the element that gives the maximum value with respect to the |
3007 | /// specified comparison function. | |
3008 | /// | |
32a655c1 | 3009 | /// If several elements are equally maximum, the last element is |
8bb4bdeb XL |
3010 | /// returned. If the iterator is empty, [`None`] is returned. |
3011 | /// | |
9e0c209e SL |
3012 | /// # Examples |
3013 | /// | |
3014 | /// ``` | |
9e0c209e SL |
3015 | /// let a = [-3_i32, 0, 1, 5, -10]; |
3016 | /// assert_eq!(*a.iter().max_by(|x, y| x.cmp(y)).unwrap(), 5); | |
3017 | /// ``` | |
3018 | #[inline] | |
476ff2be | 3019 | #[stable(feature = "iter_max_by", since = "1.15.0")] |
e1599b0c | 3020 | fn max_by<F>(self, compare: F) -> Option<Self::Item> |
dfeec247 XL |
3021 | where |
3022 | Self: Sized, | |
3023 | F: FnMut(&Self::Item, &Self::Item) -> Ordering, | |
9e0c209e | 3024 | { |
e1599b0c XL |
3025 | #[inline] |
3026 | fn fold<T>(mut compare: impl FnMut(&T, &T) -> Ordering) -> impl FnMut(T, T) -> T { | |
3027 | move |x, y| cmp::max_by(x, y, &mut compare) | |
3028 | } | |
3029 | ||
5869c6ff | 3030 | self.reduce(fold(compare)) |
9e0c209e SL |
3031 | } |
3032 | ||
a7813a04 XL |
3033 | /// Returns the element that gives the minimum value from the |
3034 | /// specified function. | |
3035 | /// | |
32a655c1 | 3036 | /// If several elements are equally minimum, the first element is |
8bb4bdeb XL |
3037 | /// returned. If the iterator is empty, [`None`] is returned. |
3038 | /// | |
a7813a04 XL |
3039 | /// # Examples |
3040 | /// | |
3041 | /// ``` | |
3042 | /// let a = [-3_i32, 0, 1, 5, -10]; | |
3043 | /// assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0); | |
3044 | /// ``` | |
e1599b0c | 3045 | #[inline] |
a7813a04 | 3046 | #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] |
e1599b0c | 3047 | fn min_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item> |
dfeec247 XL |
3048 | where |
3049 | Self: Sized, | |
3050 | F: FnMut(&Self::Item) -> B, | |
a7813a04 | 3051 | { |
e1599b0c XL |
3052 | #[inline] |
3053 | fn key<T, B>(mut f: impl FnMut(&T) -> B) -> impl FnMut(T) -> (B, T) { | |
3054 | move |x| (f(&x), x) | |
3055 | } | |
3056 | ||
3057 | #[inline] | |
3058 | fn compare<T, B: Ord>((x_p, _): &(B, T), (y_p, _): &(B, T)) -> Ordering { | |
3059 | x_p.cmp(y_p) | |
3060 | } | |
3061 | ||
3062 | let (_, x) = self.map(key(f)).min_by(compare)?; | |
3063 | Some(x) | |
a7813a04 XL |
3064 | } |
3065 | ||
9e0c209e SL |
3066 | /// Returns the element that gives the minimum value with respect to the |
3067 | /// specified comparison function. | |
3068 | /// | |
32a655c1 | 3069 | /// If several elements are equally minimum, the first element is |
8bb4bdeb XL |
3070 | /// returned. If the iterator is empty, [`None`] is returned. |
3071 | /// | |
9e0c209e SL |
3072 | /// # Examples |
3073 | /// | |
3074 | /// ``` | |
9e0c209e SL |
3075 | /// let a = [-3_i32, 0, 1, 5, -10]; |
3076 | /// assert_eq!(*a.iter().min_by(|x, y| x.cmp(y)).unwrap(), -10); | |
3077 | /// ``` | |
3078 | #[inline] | |
476ff2be | 3079 | #[stable(feature = "iter_min_by", since = "1.15.0")] |
e1599b0c | 3080 | fn min_by<F>(self, compare: F) -> Option<Self::Item> |
dfeec247 XL |
3081 | where |
3082 | Self: Sized, | |
3083 | F: FnMut(&Self::Item, &Self::Item) -> Ordering, | |
9e0c209e | 3084 | { |
e1599b0c XL |
3085 | #[inline] |
3086 | fn fold<T>(mut compare: impl FnMut(&T, &T) -> Ordering) -> impl FnMut(T, T) -> T { | |
3087 | move |x, y| cmp::min_by(x, y, &mut compare) | |
3088 | } | |
3089 | ||
5869c6ff | 3090 | self.reduce(fold(compare)) |
9e0c209e SL |
3091 | } |
3092 | ||
a7813a04 XL |
3093 | /// Reverses an iterator's direction. |
3094 | /// | |
3095 | /// Usually, iterators iterate from left to right. After using `rev()`, | |
3096 | /// an iterator will instead iterate from right to left. | |
3097 | /// | |
3098 | /// This is only possible if the iterator has an end, so `rev()` only | |
3099 | /// works on [`DoubleEndedIterator`]s. | |
3100 | /// | |
a7813a04 XL |
3101 | /// # Examples |
3102 | /// | |
3103 | /// ``` | |
3104 | /// let a = [1, 2, 3]; | |
3105 | /// | |
3106 | /// let mut iter = a.iter().rev(); | |
3107 | /// | |
3108 | /// assert_eq!(iter.next(), Some(&3)); | |
3109 | /// assert_eq!(iter.next(), Some(&2)); | |
3110 | /// assert_eq!(iter.next(), Some(&1)); | |
3111 | /// | |
3112 | /// assert_eq!(iter.next(), None); | |
3113 | /// ``` | |
3114 | #[inline] | |
6a06907d | 3115 | #[doc(alias = "reverse")] |
a7813a04 | 3116 | #[stable(feature = "rust1", since = "1.0.0")] |
dfeec247 XL |
3117 | fn rev(self) -> Rev<Self> |
3118 | where | |
3119 | Self: Sized + DoubleEndedIterator, | |
3120 | { | |
9fa01778 | 3121 | Rev::new(self) |
a7813a04 XL |
3122 | } |
3123 | ||
3124 | /// Converts an iterator of pairs into a pair of containers. | |
3125 | /// | |
3126 | /// `unzip()` consumes an entire iterator of pairs, producing two | |
3127 | /// collections: one from the left elements of the pairs, and one | |
3128 | /// from the right elements. | |
3129 | /// | |
cc61c64b | 3130 | /// This function is, in some sense, the opposite of [`zip`]. |
a7813a04 | 3131 | /// |
1b1a35ee | 3132 | /// [`zip`]: Iterator::zip |
a7813a04 XL |
3133 | /// |
3134 | /// # Examples | |
3135 | /// | |
3136 | /// Basic usage: | |
3137 | /// | |
3138 | /// ``` | |
3c0e092e | 3139 | /// let a = [(1, 2), (3, 4), (5, 6)]; |
a7813a04 XL |
3140 | /// |
3141 | /// let (left, right): (Vec<_>, Vec<_>) = a.iter().cloned().unzip(); | |
3142 | /// | |
3c0e092e XL |
3143 | /// assert_eq!(left, [1, 3, 5]); |
3144 | /// assert_eq!(right, [2, 4, 6]); | |
94222f64 XL |
3145 | /// |
3146 | /// // you can also unzip multiple nested tuples at once | |
3147 | /// let a = [(1, (2, 3)), (4, (5, 6))]; | |
3148 | /// | |
3149 | /// let (x, (y, z)): (Vec<_>, (Vec<_>, Vec<_>)) = a.iter().cloned().unzip(); | |
3150 | /// assert_eq!(x, [1, 4]); | |
3151 | /// assert_eq!(y, [2, 5]); | |
3152 | /// assert_eq!(z, [3, 6]); | |
a7813a04 XL |
3153 | /// ``` |
3154 | #[stable(feature = "rust1", since = "1.0.0")] | |
dfeec247 XL |
3155 | fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) |
3156 | where | |
a7813a04 XL |
3157 | FromA: Default + Extend<A>, |
3158 | FromB: Default + Extend<B>, | |
dfeec247 | 3159 | Self: Sized + Iterator<Item = (A, B)>, |
a7813a04 | 3160 | { |
94222f64 XL |
3161 | let mut unzipped: (FromA, FromB) = Default::default(); |
3162 | unzipped.extend(self); | |
3163 | unzipped | |
a7813a04 XL |
3164 | } |
3165 | ||
0731742a XL |
3166 | /// Creates an iterator which copies all of its elements. |
3167 | /// | |
3168 | /// This is useful when you have an iterator over `&T`, but you need an | |
3169 | /// iterator over `T`. | |
3170 | /// | |
3171 | /// # Examples | |
3172 | /// | |
3173 | /// Basic usage: | |
3174 | /// | |
3175 | /// ``` | |
0731742a XL |
3176 | /// let a = [1, 2, 3]; |
3177 | /// | |
f035d41b | 3178 | /// let v_copied: Vec<_> = a.iter().copied().collect(); |
0731742a XL |
3179 | /// |
3180 | /// // copied is the same as .map(|&x| x) | |
3181 | /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); | |
3182 | /// | |
f035d41b | 3183 | /// assert_eq!(v_copied, vec![1, 2, 3]); |
0731742a XL |
3184 | /// assert_eq!(v_map, vec![1, 2, 3]); |
3185 | /// ``` | |
48663c56 | 3186 | #[stable(feature = "iter_copied", since = "1.36.0")] |
0731742a | 3187 | fn copied<'a, T: 'a>(self) -> Copied<Self> |
dfeec247 XL |
3188 | where |
3189 | Self: Sized + Iterator<Item = &'a T>, | |
3190 | T: Copy, | |
0731742a | 3191 | { |
9fa01778 | 3192 | Copied::new(self) |
0731742a XL |
3193 | } |
3194 | ||
cc61c64b | 3195 | /// Creates an iterator which [`clone`]s all of its elements. |
a7813a04 XL |
3196 | /// |
3197 | /// This is useful when you have an iterator over `&T`, but you need an | |
3198 | /// iterator over `T`. | |
3199 | /// | |
5e7ed085 FG |
3200 | /// There is no guarantee whatsoever about the `clone` method actually |
3201 | /// being called *or* optimized away. So code should not depend on | |
3202 | /// either. | |
3203 | /// | |
1b1a35ee | 3204 | /// [`clone`]: Clone::clone |
476ff2be | 3205 | /// |
a7813a04 XL |
3206 | /// # Examples |
3207 | /// | |
3208 | /// Basic usage: | |
3209 | /// | |
3210 | /// ``` | |
3211 | /// let a = [1, 2, 3]; | |
3212 | /// | |
3213 | /// let v_cloned: Vec<_> = a.iter().cloned().collect(); | |
3214 | /// | |
3215 | /// // cloned is the same as .map(|&x| x), for integers | |
3216 | /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); | |
3217 | /// | |
3218 | /// assert_eq!(v_cloned, vec![1, 2, 3]); | |
3219 | /// assert_eq!(v_map, vec![1, 2, 3]); | |
3220 | /// ``` | |
5e7ed085 FG |
3221 | /// |
3222 | /// To get the best performance, try to clone late: | |
3223 | /// | |
3224 | /// ``` | |
3225 | /// let a = [vec![0_u8, 1, 2], vec![3, 4], vec![23]]; | |
3226 | /// // don't do this: | |
3227 | /// let slower: Vec<_> = a.iter().cloned().filter(|s| s.len() == 1).collect(); | |
3228 | /// assert_eq!(&[vec![23]], &slower[..]); | |
3229 | /// // instead call `cloned` late | |
3230 | /// let faster: Vec<_> = a.iter().filter(|s| s.len() == 1).cloned().collect(); | |
3231 | /// assert_eq!(&[vec![23]], &faster[..]); | |
3232 | /// ``` | |
a7813a04 XL |
3233 | #[stable(feature = "rust1", since = "1.0.0")] |
3234 | fn cloned<'a, T: 'a>(self) -> Cloned<Self> | |
dfeec247 XL |
3235 | where |
3236 | Self: Sized + Iterator<Item = &'a T>, | |
3237 | T: Clone, | |
a7813a04 | 3238 | { |
9fa01778 | 3239 | Cloned::new(self) |
a7813a04 XL |
3240 | } |
3241 | ||
3242 | /// Repeats an iterator endlessly. | |
3243 | /// | |
476ff2be | 3244 | /// Instead of stopping at [`None`], the iterator will instead start again, |
a7813a04 | 3245 | /// from the beginning. After iterating again, it will start at the |
a2a8927a XL |
3246 | /// beginning again. And again. And again. Forever. Note that in case the |
3247 | /// original iterator is empty, the resulting iterator will also be empty. | |
a7813a04 XL |
3248 | /// |
3249 | /// # Examples | |
3250 | /// | |
3251 | /// Basic usage: | |
3252 | /// | |
3253 | /// ``` | |
3254 | /// let a = [1, 2, 3]; | |
3255 | /// | |
3256 | /// let mut it = a.iter().cycle(); | |
3257 | /// | |
3258 | /// assert_eq!(it.next(), Some(&1)); | |
3259 | /// assert_eq!(it.next(), Some(&2)); | |
3260 | /// assert_eq!(it.next(), Some(&3)); | |
3261 | /// assert_eq!(it.next(), Some(&1)); | |
3262 | /// assert_eq!(it.next(), Some(&2)); | |
3263 | /// assert_eq!(it.next(), Some(&3)); | |
3264 | /// assert_eq!(it.next(), Some(&1)); | |
3265 | /// ``` | |
3266 | #[stable(feature = "rust1", since = "1.0.0")] | |
3267 | #[inline] | |
dfeec247 XL |
3268 | fn cycle(self) -> Cycle<Self> |
3269 | where | |
3270 | Self: Sized + Clone, | |
3271 | { | |
9fa01778 | 3272 | Cycle::new(self) |
a7813a04 XL |
3273 | } |
3274 | ||
3275 | /// Sums the elements of an iterator. | |
3276 | /// | |
3277 | /// Takes each element, adds them together, and returns the result. | |
3278 | /// | |
3279 | /// An empty iterator returns the zero value of the type. | |
3280 | /// | |
3157f602 XL |
3281 | /// # Panics |
3282 | /// | |
476ff2be | 3283 | /// When calling `sum()` and a primitive integer type is being returned, this |
9e0c209e SL |
3284 | /// method will panic if the computation overflows and debug assertions are |
3285 | /// enabled. | |
3157f602 | 3286 | /// |
a7813a04 XL |
3287 | /// # Examples |
3288 | /// | |
3289 | /// Basic usage: | |
3290 | /// | |
3291 | /// ``` | |
a7813a04 XL |
3292 | /// let a = [1, 2, 3]; |
3293 | /// let sum: i32 = a.iter().sum(); | |
3294 | /// | |
3295 | /// assert_eq!(sum, 6); | |
3296 | /// ``` | |
3157f602 XL |
3297 | #[stable(feature = "iter_arith", since = "1.11.0")] |
3298 | fn sum<S>(self) -> S | |
dfeec247 XL |
3299 | where |
3300 | Self: Sized, | |
3301 | S: Sum<Self::Item>, | |
a7813a04 | 3302 | { |
3157f602 | 3303 | Sum::sum(self) |
a7813a04 XL |
3304 | } |
3305 | ||
3306 | /// Iterates over the entire iterator, multiplying all the elements | |
3307 | /// | |
3308 | /// An empty iterator returns the one value of the type. | |
3309 | /// | |
3157f602 XL |
3310 | /// # Panics |
3311 | /// | |
476ff2be | 3312 | /// When calling `product()` and a primitive integer type is being returned, |
9e0c209e SL |
3313 | /// method will panic if the computation overflows and debug assertions are |
3314 | /// enabled. | |
3157f602 | 3315 | /// |
a7813a04 XL |
3316 | /// # Examples |
3317 | /// | |
3318 | /// ``` | |
a7813a04 | 3319 | /// fn factorial(n: u32) -> u32 { |
0731742a | 3320 | /// (1..=n).product() |
a7813a04 XL |
3321 | /// } |
3322 | /// assert_eq!(factorial(0), 1); | |
3323 | /// assert_eq!(factorial(1), 1); | |
3324 | /// assert_eq!(factorial(5), 120); | |
3325 | /// ``` | |
3157f602 XL |
3326 | #[stable(feature = "iter_arith", since = "1.11.0")] |
3327 | fn product<P>(self) -> P | |
dfeec247 XL |
3328 | where |
3329 | Self: Sized, | |
3330 | P: Product<Self::Item>, | |
a7813a04 | 3331 | { |
3157f602 | 3332 | Product::product(self) |
a7813a04 XL |
3333 | } |
3334 | ||
29967ef6 | 3335 | /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those |
a7813a04 | 3336 | /// of another. |
e1599b0c XL |
3337 | /// |
3338 | /// # Examples | |
3339 | /// | |
3340 | /// ``` | |
3341 | /// use std::cmp::Ordering; | |
3342 | /// | |
3343 | /// assert_eq!([1].iter().cmp([1].iter()), Ordering::Equal); | |
3344 | /// assert_eq!([1].iter().cmp([1, 2].iter()), Ordering::Less); | |
3345 | /// assert_eq!([1, 2].iter().cmp([1].iter()), Ordering::Greater); | |
3346 | /// ``` | |
a7813a04 | 3347 | #[stable(feature = "iter_order", since = "1.5.0")] |
e1599b0c XL |
3348 | fn cmp<I>(self, other: I) -> Ordering |
3349 | where | |
a7813a04 XL |
3350 | I: IntoIterator<Item = Self::Item>, |
3351 | Self::Item: Ord, | |
3352 | Self: Sized, | |
e1599b0c XL |
3353 | { |
3354 | self.cmp_by(other, |x, y| x.cmp(&y)) | |
3355 | } | |
3356 | ||
29967ef6 | 3357 | /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those |
e1599b0c XL |
3358 | /// of another with respect to the specified comparison function. |
3359 | /// | |
3360 | /// # Examples | |
3361 | /// | |
3362 | /// Basic usage: | |
3363 | /// | |
3364 | /// ``` | |
3365 | /// #![feature(iter_order_by)] | |
3366 | /// | |
3367 | /// use std::cmp::Ordering; | |
3368 | /// | |
3369 | /// let xs = [1, 2, 3, 4]; | |
3370 | /// let ys = [1, 4, 9, 16]; | |
3371 | /// | |
3372 | /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| x.cmp(&y)), Ordering::Less); | |
3373 | /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (x * x).cmp(&y)), Ordering::Equal); | |
3374 | /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (2 * x).cmp(&y)), Ordering::Greater); | |
3375 | /// ``` | |
e74abb32 | 3376 | #[unstable(feature = "iter_order_by", issue = "64295")] |
e1599b0c XL |
3377 | fn cmp_by<I, F>(mut self, other: I, mut cmp: F) -> Ordering |
3378 | where | |
3379 | Self: Sized, | |
3380 | I: IntoIterator, | |
3381 | F: FnMut(Self::Item, I::Item) -> Ordering, | |
a7813a04 XL |
3382 | { |
3383 | let mut other = other.into_iter(); | |
3384 | ||
3385 | loop { | |
abe05a73 | 3386 | let x = match self.next() { |
dfeec247 XL |
3387 | None => { |
3388 | if other.next().is_none() { | |
3389 | return Ordering::Equal; | |
3390 | } else { | |
3391 | return Ordering::Less; | |
3392 | } | |
3393 | } | |
abe05a73 XL |
3394 | Some(val) => val, |
3395 | }; | |
3396 | ||
3397 | let y = match other.next() { | |
3398 | None => return Ordering::Greater, | |
3399 | Some(val) => val, | |
3400 | }; | |
3401 | ||
e1599b0c | 3402 | match cmp(x, y) { |
abe05a73 XL |
3403 | Ordering::Equal => (), |
3404 | non_eq => return non_eq, | |
a7813a04 XL |
3405 | } |
3406 | } | |
3407 | } | |
3408 | ||
29967ef6 | 3409 | /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those |
a7813a04 | 3410 | /// of another. |
e1599b0c XL |
3411 | /// |
3412 | /// # Examples | |
3413 | /// | |
3414 | /// ``` | |
3415 | /// use std::cmp::Ordering; | |
3416 | /// | |
3417 | /// assert_eq!([1.].iter().partial_cmp([1.].iter()), Some(Ordering::Equal)); | |
3418 | /// assert_eq!([1.].iter().partial_cmp([1., 2.].iter()), Some(Ordering::Less)); | |
3419 | /// assert_eq!([1., 2.].iter().partial_cmp([1.].iter()), Some(Ordering::Greater)); | |
3420 | /// | |
ba9703b0 | 3421 | /// assert_eq!([f64::NAN].iter().partial_cmp([1.].iter()), None); |
e1599b0c | 3422 | /// ``` |
a7813a04 | 3423 | #[stable(feature = "iter_order", since = "1.5.0")] |
e1599b0c XL |
3424 | fn partial_cmp<I>(self, other: I) -> Option<Ordering> |
3425 | where | |
a7813a04 XL |
3426 | I: IntoIterator, |
3427 | Self::Item: PartialOrd<I::Item>, | |
3428 | Self: Sized, | |
e1599b0c XL |
3429 | { |
3430 | self.partial_cmp_by(other, |x, y| x.partial_cmp(&y)) | |
3431 | } | |
3432 | ||
29967ef6 | 3433 | /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those |
e1599b0c XL |
3434 | /// of another with respect to the specified comparison function. |
3435 | /// | |
3436 | /// # Examples | |
3437 | /// | |
3438 | /// Basic usage: | |
3439 | /// | |
3440 | /// ``` | |
3441 | /// #![feature(iter_order_by)] | |
3442 | /// | |
3443 | /// use std::cmp::Ordering; | |
3444 | /// | |
3445 | /// let xs = [1.0, 2.0, 3.0, 4.0]; | |
3446 | /// let ys = [1.0, 4.0, 9.0, 16.0]; | |
3447 | /// | |
3448 | /// assert_eq!( | |
3449 | /// xs.iter().partial_cmp_by(&ys, |&x, &y| x.partial_cmp(&y)), | |
3450 | /// Some(Ordering::Less) | |
3451 | /// ); | |
3452 | /// assert_eq!( | |
3453 | /// xs.iter().partial_cmp_by(&ys, |&x, &y| (x * x).partial_cmp(&y)), | |
3454 | /// Some(Ordering::Equal) | |
3455 | /// ); | |
3456 | /// assert_eq!( | |
3457 | /// xs.iter().partial_cmp_by(&ys, |&x, &y| (2.0 * x).partial_cmp(&y)), | |
3458 | /// Some(Ordering::Greater) | |
3459 | /// ); | |
3460 | /// ``` | |
e74abb32 | 3461 | #[unstable(feature = "iter_order_by", issue = "64295")] |
e1599b0c XL |
3462 | fn partial_cmp_by<I, F>(mut self, other: I, mut partial_cmp: F) -> Option<Ordering> |
3463 | where | |
3464 | Self: Sized, | |
3465 | I: IntoIterator, | |
3466 | F: FnMut(Self::Item, I::Item) -> Option<Ordering>, | |
a7813a04 XL |
3467 | { |
3468 | let mut other = other.into_iter(); | |
3469 | ||
3470 | loop { | |
abe05a73 | 3471 | let x = match self.next() { |
dfeec247 XL |
3472 | None => { |
3473 | if other.next().is_none() { | |
3474 | return Some(Ordering::Equal); | |
3475 | } else { | |
3476 | return Some(Ordering::Less); | |
3477 | } | |
3478 | } | |
abe05a73 XL |
3479 | Some(val) => val, |
3480 | }; | |
3481 | ||
3482 | let y = match other.next() { | |
3483 | None => return Some(Ordering::Greater), | |
3484 | Some(val) => val, | |
3485 | }; | |
3486 | ||
e1599b0c | 3487 | match partial_cmp(x, y) { |
abe05a73 XL |
3488 | Some(Ordering::Equal) => (), |
3489 | non_eq => return non_eq, | |
a7813a04 XL |
3490 | } |
3491 | } | |
3492 | } | |
3493 | ||
1b1a35ee | 3494 | /// Determines if the elements of this [`Iterator`] are equal to those of |
a7813a04 | 3495 | /// another. |
e1599b0c XL |
3496 | /// |
3497 | /// # Examples | |
3498 | /// | |
3499 | /// ``` | |
3500 | /// assert_eq!([1].iter().eq([1].iter()), true); | |
3501 | /// assert_eq!([1].iter().eq([1, 2].iter()), false); | |
3502 | /// ``` | |
a7813a04 | 3503 | #[stable(feature = "iter_order", since = "1.5.0")] |
e1599b0c XL |
3504 | fn eq<I>(self, other: I) -> bool |
3505 | where | |
a7813a04 XL |
3506 | I: IntoIterator, |
3507 | Self::Item: PartialEq<I::Item>, | |
3508 | Self: Sized, | |
e1599b0c XL |
3509 | { |
3510 | self.eq_by(other, |x, y| x == y) | |
3511 | } | |
3512 | ||
1b1a35ee | 3513 | /// Determines if the elements of this [`Iterator`] are equal to those of |
e1599b0c XL |
3514 | /// another with respect to the specified equality function. |
3515 | /// | |
3516 | /// # Examples | |
3517 | /// | |
3518 | /// Basic usage: | |
3519 | /// | |
3520 | /// ``` | |
3521 | /// #![feature(iter_order_by)] | |
3522 | /// | |
3523 | /// let xs = [1, 2, 3, 4]; | |
3524 | /// let ys = [1, 4, 9, 16]; | |
3525 | /// | |
3526 | /// assert!(xs.iter().eq_by(&ys, |&x, &y| x * x == y)); | |
3527 | /// ``` | |
e74abb32 | 3528 | #[unstable(feature = "iter_order_by", issue = "64295")] |
e1599b0c XL |
3529 | fn eq_by<I, F>(mut self, other: I, mut eq: F) -> bool |
3530 | where | |
3531 | Self: Sized, | |
3532 | I: IntoIterator, | |
3533 | F: FnMut(Self::Item, I::Item) -> bool, | |
a7813a04 XL |
3534 | { |
3535 | let mut other = other.into_iter(); | |
3536 | ||
3537 | loop { | |
abe05a73 XL |
3538 | let x = match self.next() { |
3539 | None => return other.next().is_none(), | |
3540 | Some(val) => val, | |
3541 | }; | |
3542 | ||
3543 | let y = match other.next() { | |
3544 | None => return false, | |
3545 | Some(val) => val, | |
3546 | }; | |
3547 | ||
e1599b0c XL |
3548 | if !eq(x, y) { |
3549 | return false; | |
3550 | } | |
a7813a04 XL |
3551 | } |
3552 | } | |
3553 | ||
1b1a35ee | 3554 | /// Determines if the elements of this [`Iterator`] are unequal to those of |
a7813a04 | 3555 | /// another. |
e1599b0c XL |
3556 | /// |
3557 | /// # Examples | |
3558 | /// | |
3559 | /// ``` | |
3560 | /// assert_eq!([1].iter().ne([1].iter()), false); | |
3561 | /// assert_eq!([1].iter().ne([1, 2].iter()), true); | |
3562 | /// ``` | |
a7813a04 | 3563 | #[stable(feature = "iter_order", since = "1.5.0")] |
dfeec247 XL |
3564 | fn ne<I>(self, other: I) -> bool |
3565 | where | |
a7813a04 XL |
3566 | I: IntoIterator, |
3567 | Self::Item: PartialEq<I::Item>, | |
3568 | Self: Sized, | |
3569 | { | |
532ac7d7 | 3570 | !self.eq(other) |
a7813a04 XL |
3571 | } |
3572 | ||
29967ef6 | 3573 | /// Determines if the elements of this [`Iterator`] are [lexicographically](Ord#lexicographical-comparison) |
a7813a04 | 3574 | /// less than those of another. |
e1599b0c XL |
3575 | /// |
3576 | /// # Examples | |
3577 | /// | |
3578 | /// ``` | |
3579 | /// assert_eq!([1].iter().lt([1].iter()), false); | |
3580 | /// assert_eq!([1].iter().lt([1, 2].iter()), true); | |
3581 | /// assert_eq!([1, 2].iter().lt([1].iter()), false); | |
1b1a35ee | 3582 | /// assert_eq!([1, 2].iter().lt([1, 2].iter()), false); |
e1599b0c | 3583 | /// ``` |
a7813a04 | 3584 | #[stable(feature = "iter_order", since = "1.5.0")] |
dfeec247 XL |
3585 | fn lt<I>(self, other: I) -> bool |
3586 | where | |
a7813a04 XL |
3587 | I: IntoIterator, |
3588 | Self::Item: PartialOrd<I::Item>, | |
3589 | Self: Sized, | |
3590 | { | |
532ac7d7 | 3591 | self.partial_cmp(other) == Some(Ordering::Less) |
a7813a04 XL |
3592 | } |
3593 | ||
29967ef6 | 3594 | /// Determines if the elements of this [`Iterator`] are [lexicographically](Ord#lexicographical-comparison) |
a7813a04 | 3595 | /// less or equal to those of another. |
e1599b0c XL |
3596 | /// |
3597 | /// # Examples | |
3598 | /// | |
3599 | /// ``` | |
3600 | /// assert_eq!([1].iter().le([1].iter()), true); | |
3601 | /// assert_eq!([1].iter().le([1, 2].iter()), true); | |
3602 | /// assert_eq!([1, 2].iter().le([1].iter()), false); | |
1b1a35ee | 3603 | /// assert_eq!([1, 2].iter().le([1, 2].iter()), true); |
e1599b0c | 3604 | /// ``` |
a7813a04 | 3605 | #[stable(feature = "iter_order", since = "1.5.0")] |
dfeec247 XL |
3606 | fn le<I>(self, other: I) -> bool |
3607 | where | |
a7813a04 XL |
3608 | I: IntoIterator, |
3609 | Self::Item: PartialOrd<I::Item>, | |
3610 | Self: Sized, | |
3611 | { | |
ba9703b0 | 3612 | matches!(self.partial_cmp(other), Some(Ordering::Less | Ordering::Equal)) |
a7813a04 XL |
3613 | } |
3614 | ||
29967ef6 | 3615 | /// Determines if the elements of this [`Iterator`] are [lexicographically](Ord#lexicographical-comparison) |
a7813a04 | 3616 | /// greater than those of another. |
e1599b0c XL |
3617 | /// |
3618 | /// # Examples | |
3619 | /// | |
3620 | /// ``` | |
3621 | /// assert_eq!([1].iter().gt([1].iter()), false); | |
3622 | /// assert_eq!([1].iter().gt([1, 2].iter()), false); | |
3623 | /// assert_eq!([1, 2].iter().gt([1].iter()), true); | |
1b1a35ee | 3624 | /// assert_eq!([1, 2].iter().gt([1, 2].iter()), false); |
e1599b0c | 3625 | /// ``` |
a7813a04 | 3626 | #[stable(feature = "iter_order", since = "1.5.0")] |
dfeec247 XL |
3627 | fn gt<I>(self, other: I) -> bool |
3628 | where | |
a7813a04 XL |
3629 | I: IntoIterator, |
3630 | Self::Item: PartialOrd<I::Item>, | |
3631 | Self: Sized, | |
3632 | { | |
532ac7d7 | 3633 | self.partial_cmp(other) == Some(Ordering::Greater) |
a7813a04 XL |
3634 | } |
3635 | ||
29967ef6 | 3636 | /// Determines if the elements of this [`Iterator`] are [lexicographically](Ord#lexicographical-comparison) |
a7813a04 | 3637 | /// greater than or equal to those of another. |
e1599b0c XL |
3638 | /// |
3639 | /// # Examples | |
3640 | /// | |
3641 | /// ``` | |
3642 | /// assert_eq!([1].iter().ge([1].iter()), true); | |
3643 | /// assert_eq!([1].iter().ge([1, 2].iter()), false); | |
3644 | /// assert_eq!([1, 2].iter().ge([1].iter()), true); | |
1b1a35ee | 3645 | /// assert_eq!([1, 2].iter().ge([1, 2].iter()), true); |
e1599b0c | 3646 | /// ``` |
a7813a04 | 3647 | #[stable(feature = "iter_order", since = "1.5.0")] |
dfeec247 XL |
3648 | fn ge<I>(self, other: I) -> bool |
3649 | where | |
a7813a04 XL |
3650 | I: IntoIterator, |
3651 | Self::Item: PartialOrd<I::Item>, | |
3652 | Self: Sized, | |
3653 | { | |
ba9703b0 | 3654 | matches!(self.partial_cmp(other), Some(Ordering::Greater | Ordering::Equal)) |
a7813a04 | 3655 | } |
9fa01778 XL |
3656 | |
3657 | /// Checks if the elements of this iterator are sorted. | |
3658 | /// | |
3659 | /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the | |
3660 | /// iterator yields exactly zero or one element, `true` is returned. | |
3661 | /// | |
3662 | /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition | |
3663 | /// implies that this function returns `false` if any two consecutive items are not | |
3664 | /// comparable. | |
3665 | /// | |
3666 | /// # Examples | |
3667 | /// | |
3668 | /// ``` | |
3669 | /// #![feature(is_sorted)] | |
3670 | /// | |
3671 | /// assert!([1, 2, 2, 9].iter().is_sorted()); | |
3672 | /// assert!(![1, 3, 2, 4].iter().is_sorted()); | |
3673 | /// assert!([0].iter().is_sorted()); | |
3674 | /// assert!(std::iter::empty::<i32>().is_sorted()); | |
ba9703b0 | 3675 | /// assert!(![0.0, 1.0, f32::NAN].iter().is_sorted()); |
9fa01778 XL |
3676 | /// ``` |
3677 | #[inline] | |
3678 | #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] | |
3679 | fn is_sorted(self) -> bool | |
3680 | where | |
3681 | Self: Sized, | |
3682 | Self::Item: PartialOrd, | |
3683 | { | |
e1599b0c | 3684 | self.is_sorted_by(PartialOrd::partial_cmp) |
9fa01778 XL |
3685 | } |
3686 | ||
3687 | /// Checks if the elements of this iterator are sorted using the given comparator function. | |
3688 | /// | |
3689 | /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare` | |
3690 | /// function to determine the ordering of two elements. Apart from that, it's equivalent to | |
3691 | /// [`is_sorted`]; see its documentation for more information. | |
3692 | /// | |
e1599b0c XL |
3693 | /// # Examples |
3694 | /// | |
3695 | /// ``` | |
3696 | /// #![feature(is_sorted)] | |
3697 | /// | |
3698 | /// assert!([1, 2, 2, 9].iter().is_sorted_by(|a, b| a.partial_cmp(b))); | |
3699 | /// assert!(![1, 3, 2, 4].iter().is_sorted_by(|a, b| a.partial_cmp(b))); | |
3700 | /// assert!([0].iter().is_sorted_by(|a, b| a.partial_cmp(b))); | |
3701 | /// assert!(std::iter::empty::<i32>().is_sorted_by(|a, b| a.partial_cmp(b))); | |
ba9703b0 | 3702 | /// assert!(![0.0, 1.0, f32::NAN].iter().is_sorted_by(|a, b| a.partial_cmp(b))); |
e1599b0c XL |
3703 | /// ``` |
3704 | /// | |
1b1a35ee | 3705 | /// [`is_sorted`]: Iterator::is_sorted |
9fa01778 | 3706 | #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] |
6a06907d | 3707 | fn is_sorted_by<F>(mut self, compare: F) -> bool |
9fa01778 XL |
3708 | where |
3709 | Self: Sized, | |
dfeec247 | 3710 | F: FnMut(&Self::Item, &Self::Item) -> Option<Ordering>, |
9fa01778 | 3711 | { |
6a06907d XL |
3712 | #[inline] |
3713 | fn check<'a, T>( | |
3714 | last: &'a mut T, | |
3715 | mut compare: impl FnMut(&T, &T) -> Option<Ordering> + 'a, | |
3716 | ) -> impl FnMut(T) -> bool + 'a { | |
3717 | move |curr| { | |
3718 | if let Some(Ordering::Greater) | None = compare(&last, &curr) { | |
3719 | return false; | |
3720 | } | |
3721 | *last = curr; | |
3722 | true | |
3723 | } | |
3724 | } | |
3725 | ||
9fa01778 XL |
3726 | let mut last = match self.next() { |
3727 | Some(e) => e, | |
3728 | None => return true, | |
3729 | }; | |
3730 | ||
6a06907d | 3731 | self.all(check(&mut last, compare)) |
9fa01778 XL |
3732 | } |
3733 | ||
3734 | /// Checks if the elements of this iterator are sorted using the given key extraction | |
3735 | /// function. | |
3736 | /// | |
3737 | /// Instead of comparing the iterator's elements directly, this function compares the keys of | |
3738 | /// the elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see | |
3739 | /// its documentation for more information. | |
3740 | /// | |
1b1a35ee | 3741 | /// [`is_sorted`]: Iterator::is_sorted |
9fa01778 XL |
3742 | /// |
3743 | /// # Examples | |
3744 | /// | |
3745 | /// ``` | |
3746 | /// #![feature(is_sorted)] | |
3747 | /// | |
3748 | /// assert!(["c", "bb", "aaa"].iter().is_sorted_by_key(|s| s.len())); | |
3749 | /// assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs())); | |
3750 | /// ``` | |
3751 | #[inline] | |
3752 | #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] | |
416331ca | 3753 | fn is_sorted_by_key<F, K>(self, f: F) -> bool |
9fa01778 XL |
3754 | where |
3755 | Self: Sized, | |
416331ca | 3756 | F: FnMut(Self::Item) -> K, |
dfeec247 | 3757 | K: PartialOrd, |
9fa01778 | 3758 | { |
416331ca | 3759 | self.map(f).is_sorted() |
9fa01778 | 3760 | } |
3dfed10e | 3761 | |
94222f64 | 3762 | /// See [TrustedRandomAccess][super::super::TrustedRandomAccess] |
1b1a35ee XL |
3763 | // The unusual name is to avoid name collisions in method resolution |
3764 | // see #76479. | |
3dfed10e XL |
3765 | #[inline] |
3766 | #[doc(hidden)] | |
3767 | #[unstable(feature = "trusted_random_access", issue = "none")] | |
6c58768f | 3768 | unsafe fn __iterator_get_unchecked(&mut self, _idx: usize) -> Self::Item |
3dfed10e | 3769 | where |
94222f64 | 3770 | Self: TrustedRandomAccessNoCoerce, |
3dfed10e XL |
3771 | { |
3772 | unreachable!("Always specialized"); | |
3773 | } | |
a7813a04 XL |
3774 | } |
3775 | ||
a7813a04 | 3776 | #[stable(feature = "rust1", since = "1.0.0")] |
0bf4aa26 | 3777 | impl<I: Iterator + ?Sized> Iterator for &mut I { |
a7813a04 | 3778 | type Item = I::Item; |
c295e0f8 | 3779 | #[inline] |
dfeec247 XL |
3780 | fn next(&mut self) -> Option<I::Item> { |
3781 | (**self).next() | |
3782 | } | |
3783 | fn size_hint(&self) -> (usize, Option<usize>) { | |
3784 | (**self).size_hint() | |
3785 | } | |
1b1a35ee XL |
3786 | fn advance_by(&mut self, n: usize) -> Result<(), usize> { |
3787 | (**self).advance_by(n) | |
3788 | } | |
476ff2be SL |
3789 | fn nth(&mut self, n: usize) -> Option<Self::Item> { |
3790 | (**self).nth(n) | |
3791 | } | |
a7813a04 | 3792 | } |