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48663c56 XL |
1 | use crate::cmp::Ordering; |
2 | use crate::ops::Try; | |
a7813a04 | 3 | |
9fa01778 XL |
4 | use super::super::LoopState; |
5 | use super::super::{Chain, Cycle, Copied, Cloned, Enumerate, Filter, FilterMap, Fuse}; | |
6 | use super::super::{Flatten, FlatMap}; | |
7 | use super::super::{Inspect, Map, Peekable, Scan, Skip, SkipWhile, StepBy, Take, TakeWhile, Rev}; | |
8 | use super::super::{Zip, Sum, Product, FromIterator}; | |
a7813a04 | 9 | |
8faf50e0 | 10 | fn _assert_is_object_safe(_: &dyn Iterator<Item=()>) {} |
a7813a04 XL |
11 | |
12 | /// An interface for dealing with iterators. | |
13 | /// | |
14 | /// This is the main iterator trait. For more about the concept of iterators | |
15 | /// generally, please see the [module-level documentation]. In particular, you | |
16 | /// may want to know how to [implement `Iterator`][impl]. | |
17 | /// | |
18 | /// [module-level documentation]: index.html | |
19 | /// [impl]: index.html#implementing-iterator | |
20 | #[stable(feature = "rust1", since = "1.0.0")] | |
2c00a5a8 | 21 | #[rustc_on_unimplemented( |
0bf4aa26 XL |
22 | on( |
23 | _Self="[std::ops::Range<Idx>; 1]", | |
24 | label="if you meant to iterate between two values, remove the square brackets", | |
25 | note="`[start..end]` is an array of one `Range`; you might have meant to have a `Range` \ | |
26 | without the brackets: `start..end`" | |
27 | ), | |
28 | on( | |
29 | _Self="[std::ops::RangeFrom<Idx>; 1]", | |
30 | label="if you meant to iterate from a value onwards, remove the square brackets", | |
31 | note="`[start..]` is an array of one `RangeFrom`; you might have meant to have a \ | |
32 | `RangeFrom` without the brackets: `start..`, keeping in mind that iterating over an \ | |
33 | unbounded iterator will run forever unless you `break` or `return` from within the \ | |
34 | loop" | |
35 | ), | |
36 | on( | |
37 | _Self="[std::ops::RangeTo<Idx>; 1]", | |
38 | label="if you meant to iterate until a value, remove the square brackets and add a \ | |
39 | starting value", | |
40 | note="`[..end]` is an array of one `RangeTo`; you might have meant to have a bounded \ | |
41 | `Range` without the brackets: `0..end`" | |
42 | ), | |
43 | on( | |
44 | _Self="[std::ops::RangeInclusive<Idx>; 1]", | |
45 | label="if you meant to iterate between two values, remove the square brackets", | |
46 | note="`[start..=end]` is an array of one `RangeInclusive`; you might have meant to have a \ | |
47 | `RangeInclusive` without the brackets: `start..=end`" | |
48 | ), | |
49 | on( | |
50 | _Self="[std::ops::RangeToInclusive<Idx>; 1]", | |
51 | label="if you meant to iterate until a value (including it), remove the square brackets \ | |
52 | and add a starting value", | |
53 | note="`[..=end]` is an array of one `RangeToInclusive`; you might have meant to have a \ | |
54 | bounded `RangeInclusive` without the brackets: `0..=end`" | |
55 | ), | |
56 | on( | |
57 | _Self="std::ops::RangeTo<Idx>", | |
58 | label="if you meant to iterate until a value, add a starting value", | |
59 | note="`..end` is a `RangeTo`, which cannot be iterated on; you might have meant to have a \ | |
60 | bounded `Range`: `0..end`" | |
61 | ), | |
62 | on( | |
63 | _Self="std::ops::RangeToInclusive<Idx>", | |
64 | label="if you meant to iterate until a value (including it), add a starting value", | |
65 | note="`..=end` is a `RangeToInclusive`, which cannot be iterated on; you might have meant \ | |
66 | to have a bounded `RangeInclusive`: `0..=end`" | |
67 | ), | |
2c00a5a8 XL |
68 | on( |
69 | _Self="&str", | |
70 | label="`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`" | |
71 | ), | |
0bf4aa26 XL |
72 | on( |
73 | _Self="std::string::String", | |
74 | label="`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`" | |
75 | ), | |
76 | on( | |
77 | _Self="[]", | |
78 | label="borrow the array with `&` or call `.iter()` on it to iterate over it", | |
0731742a | 79 | note="arrays are not iterators, but slices like the following are: `&[1, 2, 3]`" |
0bf4aa26 XL |
80 | ), |
81 | on( | |
82 | _Self="{integral}", | |
83 | note="if you want to iterate between `start` until a value `end`, use the exclusive range \ | |
84 | syntax `start..end` or the inclusive range syntax `start..=end`" | |
85 | ), | |
86 | label="`{Self}` is not an iterator", | |
87 | message="`{Self}` is not an iterator" | |
2c00a5a8 | 88 | )] |
ff7c6d11 | 89 | #[doc(spotlight)] |
0731742a | 90 | #[must_use = "iterators are lazy and do nothing unless consumed"] |
a7813a04 XL |
91 | pub trait Iterator { |
92 | /// The type of the elements being iterated over. | |
93 | #[stable(feature = "rust1", since = "1.0.0")] | |
94 | type Item; | |
95 | ||
96 | /// Advances the iterator and returns the next value. | |
97 | /// | |
476ff2be | 98 | /// Returns [`None`] when iteration is finished. Individual iterator |
a7813a04 | 99 | /// implementations may choose to resume iteration, and so calling `next()` |
476ff2be | 100 | /// again may or may not eventually start returning [`Some(Item)`] again at some |
a7813a04 XL |
101 | /// point. |
102 | /// | |
476ff2be SL |
103 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
104 | /// [`Some(Item)`]: ../../std/option/enum.Option.html#variant.Some | |
105 | /// | |
a7813a04 XL |
106 | /// # Examples |
107 | /// | |
108 | /// Basic usage: | |
109 | /// | |
110 | /// ``` | |
111 | /// let a = [1, 2, 3]; | |
112 | /// | |
113 | /// let mut iter = a.iter(); | |
114 | /// | |
115 | /// // A call to next() returns the next value... | |
116 | /// assert_eq!(Some(&1), iter.next()); | |
117 | /// assert_eq!(Some(&2), iter.next()); | |
118 | /// assert_eq!(Some(&3), iter.next()); | |
119 | /// | |
120 | /// // ... and then None once it's over. | |
121 | /// assert_eq!(None, iter.next()); | |
122 | /// | |
9fa01778 | 123 | /// // More calls may or may not return `None`. Here, they always will. |
a7813a04 XL |
124 | /// assert_eq!(None, iter.next()); |
125 | /// assert_eq!(None, iter.next()); | |
126 | /// ``` | |
127 | #[stable(feature = "rust1", since = "1.0.0")] | |
128 | fn next(&mut self) -> Option<Self::Item>; | |
129 | ||
130 | /// Returns the bounds on the remaining length of the iterator. | |
131 | /// | |
132 | /// Specifically, `size_hint()` returns a tuple where the first element | |
133 | /// is the lower bound, and the second element is the upper bound. | |
134 | /// | |
476ff2be SL |
135 | /// The second half of the tuple that is returned is an [`Option`]`<`[`usize`]`>`. |
136 | /// A [`None`] here means that either there is no known upper bound, or the | |
137 | /// upper bound is larger than [`usize`]. | |
a7813a04 XL |
138 | /// |
139 | /// # Implementation notes | |
140 | /// | |
141 | /// It is not enforced that an iterator implementation yields the declared | |
142 | /// number of elements. A buggy iterator may yield less than the lower bound | |
143 | /// or more than the upper bound of elements. | |
144 | /// | |
145 | /// `size_hint()` is primarily intended to be used for optimizations such as | |
146 | /// reserving space for the elements of the iterator, but must not be | |
0731742a | 147 | /// trusted to e.g., omit bounds checks in unsafe code. An incorrect |
a7813a04 XL |
148 | /// implementation of `size_hint()` should not lead to memory safety |
149 | /// violations. | |
150 | /// | |
151 | /// That said, the implementation should provide a correct estimation, | |
152 | /// because otherwise it would be a violation of the trait's protocol. | |
153 | /// | |
0731742a | 154 | /// The default implementation returns `(0, `[`None`]`)` which is correct for any |
a7813a04 XL |
155 | /// iterator. |
156 | /// | |
476ff2be SL |
157 | /// [`usize`]: ../../std/primitive.usize.html |
158 | /// [`Option`]: ../../std/option/enum.Option.html | |
159 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
160 | /// | |
a7813a04 XL |
161 | /// # Examples |
162 | /// | |
163 | /// Basic usage: | |
164 | /// | |
165 | /// ``` | |
166 | /// let a = [1, 2, 3]; | |
167 | /// let iter = a.iter(); | |
168 | /// | |
169 | /// assert_eq!((3, Some(3)), iter.size_hint()); | |
170 | /// ``` | |
171 | /// | |
172 | /// A more complex example: | |
173 | /// | |
174 | /// ``` | |
175 | /// // The even numbers from zero to ten. | |
176 | /// let iter = (0..10).filter(|x| x % 2 == 0); | |
177 | /// | |
178 | /// // We might iterate from zero to ten times. Knowing that it's five | |
179 | /// // exactly wouldn't be possible without executing filter(). | |
180 | /// assert_eq!((0, Some(10)), iter.size_hint()); | |
181 | /// | |
7cac9316 | 182 | /// // Let's add five more numbers with chain() |
a7813a04 XL |
183 | /// let iter = (0..10).filter(|x| x % 2 == 0).chain(15..20); |
184 | /// | |
185 | /// // now both bounds are increased by five | |
186 | /// assert_eq!((5, Some(15)), iter.size_hint()); | |
187 | /// ``` | |
188 | /// | |
189 | /// Returning `None` for an upper bound: | |
190 | /// | |
191 | /// ``` | |
192 | /// // an infinite iterator has no upper bound | |
7cac9316 | 193 | /// // and the maximum possible lower bound |
a7813a04 XL |
194 | /// let iter = 0..; |
195 | /// | |
7cac9316 | 196 | /// assert_eq!((usize::max_value(), None), iter.size_hint()); |
a7813a04 XL |
197 | /// ``` |
198 | #[inline] | |
199 | #[stable(feature = "rust1", since = "1.0.0")] | |
200 | fn size_hint(&self) -> (usize, Option<usize>) { (0, None) } | |
201 | ||
202 | /// Consumes the iterator, counting the number of iterations and returning it. | |
203 | /// | |
cc61c64b | 204 | /// This method will evaluate the iterator until its [`next`] returns |
476ff2be | 205 | /// [`None`]. Once [`None`] is encountered, `count()` returns the number of |
cc61c64b | 206 | /// times it called [`next`]. |
a7813a04 | 207 | /// |
cc61c64b | 208 | /// [`next`]: #tymethod.next |
476ff2be | 209 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
a7813a04 XL |
210 | /// |
211 | /// # Overflow Behavior | |
212 | /// | |
213 | /// The method does no guarding against overflows, so counting elements of | |
476ff2be | 214 | /// an iterator with more than [`usize::MAX`] elements either produces the |
a7813a04 XL |
215 | /// wrong result or panics. If debug assertions are enabled, a panic is |
216 | /// guaranteed. | |
217 | /// | |
218 | /// # Panics | |
219 | /// | |
476ff2be | 220 | /// This function might panic if the iterator has more than [`usize::MAX`] |
a7813a04 XL |
221 | /// elements. |
222 | /// | |
0531ce1d | 223 | /// [`usize::MAX`]: ../../std/usize/constant.MAX.html |
476ff2be | 224 | /// |
a7813a04 XL |
225 | /// # Examples |
226 | /// | |
227 | /// Basic usage: | |
228 | /// | |
229 | /// ``` | |
230 | /// let a = [1, 2, 3]; | |
231 | /// assert_eq!(a.iter().count(), 3); | |
232 | /// | |
233 | /// let a = [1, 2, 3, 4, 5]; | |
234 | /// assert_eq!(a.iter().count(), 5); | |
235 | /// ``` | |
236 | #[inline] | |
3157f602 | 237 | #[rustc_inherit_overflow_checks] |
a7813a04 XL |
238 | #[stable(feature = "rust1", since = "1.0.0")] |
239 | fn count(self) -> usize where Self: Sized { | |
240 | // Might overflow. | |
241 | self.fold(0, |cnt, _| cnt + 1) | |
242 | } | |
243 | ||
244 | /// Consumes the iterator, returning the last element. | |
245 | /// | |
476ff2be SL |
246 | /// This method will evaluate the iterator until it returns [`None`]. While |
247 | /// doing so, it keeps track of the current element. After [`None`] is | |
a7813a04 XL |
248 | /// returned, `last()` will then return the last element it saw. |
249 | /// | |
476ff2be SL |
250 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
251 | /// | |
a7813a04 XL |
252 | /// # Examples |
253 | /// | |
254 | /// Basic usage: | |
255 | /// | |
256 | /// ``` | |
257 | /// let a = [1, 2, 3]; | |
258 | /// assert_eq!(a.iter().last(), Some(&3)); | |
259 | /// | |
260 | /// let a = [1, 2, 3, 4, 5]; | |
261 | /// assert_eq!(a.iter().last(), Some(&5)); | |
262 | /// ``` | |
263 | #[inline] | |
264 | #[stable(feature = "rust1", since = "1.0.0")] | |
265 | fn last(self) -> Option<Self::Item> where Self: Sized { | |
416331ca | 266 | self.fold(None, |_, x| Some(x)) |
a7813a04 XL |
267 | } |
268 | ||
c30ab7b3 | 269 | /// Returns the `n`th element of the iterator. |
a7813a04 | 270 | /// |
a7813a04 XL |
271 | /// Like most indexing operations, the count starts from zero, so `nth(0)` |
272 | /// returns the first value, `nth(1)` the second, and so on. | |
273 | /// | |
8bb4bdeb XL |
274 | /// Note that all preceding elements, as well as the returned element, will be |
275 | /// consumed from the iterator. That means that the preceding elements will be | |
276 | /// discarded, and also that calling `nth(0)` multiple times on the same iterator | |
277 | /// will return different elements. | |
278 | /// | |
476ff2be | 279 | /// `nth()` will return [`None`] if `n` is greater than or equal to the length of the |
a7813a04 XL |
280 | /// iterator. |
281 | /// | |
476ff2be SL |
282 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
283 | /// | |
a7813a04 XL |
284 | /// # Examples |
285 | /// | |
286 | /// Basic usage: | |
287 | /// | |
288 | /// ``` | |
289 | /// let a = [1, 2, 3]; | |
290 | /// assert_eq!(a.iter().nth(1), Some(&2)); | |
291 | /// ``` | |
292 | /// | |
293 | /// Calling `nth()` multiple times doesn't rewind the iterator: | |
294 | /// | |
295 | /// ``` | |
296 | /// let a = [1, 2, 3]; | |
297 | /// | |
298 | /// let mut iter = a.iter(); | |
299 | /// | |
300 | /// assert_eq!(iter.nth(1), Some(&2)); | |
301 | /// assert_eq!(iter.nth(1), None); | |
302 | /// ``` | |
303 | /// | |
304 | /// Returning `None` if there are less than `n + 1` elements: | |
305 | /// | |
306 | /// ``` | |
307 | /// let a = [1, 2, 3]; | |
308 | /// assert_eq!(a.iter().nth(10), None); | |
309 | /// ``` | |
310 | #[inline] | |
311 | #[stable(feature = "rust1", since = "1.0.0")] | |
476ff2be | 312 | fn nth(&mut self, mut n: usize) -> Option<Self::Item> { |
a7813a04 XL |
313 | for x in self { |
314 | if n == 0 { return Some(x) } | |
315 | n -= 1; | |
316 | } | |
317 | None | |
318 | } | |
319 | ||
7cac9316 XL |
320 | /// Creates an iterator starting at the same point, but stepping by |
321 | /// the given amount at each iteration. | |
322 | /// | |
94b46f34 | 323 | /// Note 1: The first element of the iterator will always be returned, |
7cac9316 XL |
324 | /// regardless of the step given. |
325 | /// | |
94b46f34 XL |
326 | /// Note 2: The time at which ignored elements are pulled is not fixed. |
327 | /// `StepBy` behaves like the sequence `next(), nth(step-1), nth(step-1), …`, | |
328 | /// but is also free to behave like the sequence | |
329 | /// `advance_n_and_return_first(step), advance_n_and_return_first(step), …` | |
330 | /// Which way is used may change for some iterators for performance reasons. | |
331 | /// The second way will advance the iterator earlier and may consume more items. | |
332 | /// | |
333 | /// `advance_n_and_return_first` is the equivalent of: | |
334 | /// ``` | |
335 | /// fn advance_n_and_return_first<I>(iter: &mut I, total_step: usize) -> Option<I::Item> | |
336 | /// where | |
337 | /// I: Iterator, | |
338 | /// { | |
339 | /// let next = iter.next(); | |
340 | /// if total_step > 1 { | |
341 | /// iter.nth(total_step-2); | |
342 | /// } | |
343 | /// next | |
344 | /// } | |
345 | /// ``` | |
346 | /// | |
7cac9316 XL |
347 | /// # Panics |
348 | /// | |
349 | /// The method will panic if the given step is `0`. | |
350 | /// | |
351 | /// # Examples | |
352 | /// | |
353 | /// Basic usage: | |
354 | /// | |
355 | /// ``` | |
7cac9316 | 356 | /// let a = [0, 1, 2, 3, 4, 5]; |
48663c56 | 357 | /// let mut iter = a.iter().step_by(2); |
7cac9316 XL |
358 | /// |
359 | /// assert_eq!(iter.next(), Some(&0)); | |
360 | /// assert_eq!(iter.next(), Some(&2)); | |
361 | /// assert_eq!(iter.next(), Some(&4)); | |
362 | /// assert_eq!(iter.next(), None); | |
363 | /// ``` | |
364 | #[inline] | |
94b46f34 | 365 | #[stable(feature = "iterator_step_by", since = "1.28.0")] |
7cac9316 | 366 | fn step_by(self, step: usize) -> StepBy<Self> where Self: Sized { |
9fa01778 | 367 | StepBy::new(self, step) |
7cac9316 XL |
368 | } |
369 | ||
a7813a04 XL |
370 | /// Takes two iterators and creates a new iterator over both in sequence. |
371 | /// | |
372 | /// `chain()` will return a new iterator which will first iterate over | |
373 | /// values from the first iterator and then over values from the second | |
374 | /// iterator. | |
375 | /// | |
376 | /// In other words, it links two iterators together, in a chain. 🔗 | |
377 | /// | |
378 | /// # Examples | |
379 | /// | |
380 | /// Basic usage: | |
381 | /// | |
382 | /// ``` | |
383 | /// let a1 = [1, 2, 3]; | |
384 | /// let a2 = [4, 5, 6]; | |
385 | /// | |
386 | /// let mut iter = a1.iter().chain(a2.iter()); | |
387 | /// | |
388 | /// assert_eq!(iter.next(), Some(&1)); | |
389 | /// assert_eq!(iter.next(), Some(&2)); | |
390 | /// assert_eq!(iter.next(), Some(&3)); | |
391 | /// assert_eq!(iter.next(), Some(&4)); | |
392 | /// assert_eq!(iter.next(), Some(&5)); | |
393 | /// assert_eq!(iter.next(), Some(&6)); | |
394 | /// assert_eq!(iter.next(), None); | |
395 | /// ``` | |
396 | /// | |
397 | /// Since the argument to `chain()` uses [`IntoIterator`], we can pass | |
398 | /// anything that can be converted into an [`Iterator`], not just an | |
399 | /// [`Iterator`] itself. For example, slices (`&[T]`) implement | |
400 | /// [`IntoIterator`], and so can be passed to `chain()` directly: | |
401 | /// | |
402 | /// [`IntoIterator`]: trait.IntoIterator.html | |
403 | /// [`Iterator`]: trait.Iterator.html | |
404 | /// | |
405 | /// ``` | |
406 | /// let s1 = &[1, 2, 3]; | |
407 | /// let s2 = &[4, 5, 6]; | |
408 | /// | |
409 | /// let mut iter = s1.iter().chain(s2); | |
410 | /// | |
411 | /// assert_eq!(iter.next(), Some(&1)); | |
412 | /// assert_eq!(iter.next(), Some(&2)); | |
413 | /// assert_eq!(iter.next(), Some(&3)); | |
414 | /// assert_eq!(iter.next(), Some(&4)); | |
415 | /// assert_eq!(iter.next(), Some(&5)); | |
416 | /// assert_eq!(iter.next(), Some(&6)); | |
417 | /// assert_eq!(iter.next(), None); | |
418 | /// ``` | |
419 | #[inline] | |
420 | #[stable(feature = "rust1", since = "1.0.0")] | |
421 | fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> where | |
422 | Self: Sized, U: IntoIterator<Item=Self::Item>, | |
423 | { | |
9fa01778 | 424 | Chain::new(self, other.into_iter()) |
a7813a04 XL |
425 | } |
426 | ||
427 | /// 'Zips up' two iterators into a single iterator of pairs. | |
428 | /// | |
429 | /// `zip()` returns a new iterator that will iterate over two other | |
430 | /// iterators, returning a tuple where the first element comes from the | |
431 | /// first iterator, and the second element comes from the second iterator. | |
432 | /// | |
433 | /// In other words, it zips two iterators together, into a single one. | |
434 | /// | |
8faf50e0 XL |
435 | /// If either iterator returns [`None`], [`next`] from the zipped iterator |
436 | /// will return [`None`]. If the first iterator returns [`None`], `zip` will | |
437 | /// short-circuit and `next` will not be called on the second iterator. | |
a7813a04 XL |
438 | /// |
439 | /// # Examples | |
440 | /// | |
441 | /// Basic usage: | |
442 | /// | |
443 | /// ``` | |
444 | /// let a1 = [1, 2, 3]; | |
445 | /// let a2 = [4, 5, 6]; | |
446 | /// | |
447 | /// let mut iter = a1.iter().zip(a2.iter()); | |
448 | /// | |
449 | /// assert_eq!(iter.next(), Some((&1, &4))); | |
450 | /// assert_eq!(iter.next(), Some((&2, &5))); | |
451 | /// assert_eq!(iter.next(), Some((&3, &6))); | |
452 | /// assert_eq!(iter.next(), None); | |
453 | /// ``` | |
454 | /// | |
455 | /// Since the argument to `zip()` uses [`IntoIterator`], we can pass | |
456 | /// anything that can be converted into an [`Iterator`], not just an | |
457 | /// [`Iterator`] itself. For example, slices (`&[T]`) implement | |
458 | /// [`IntoIterator`], and so can be passed to `zip()` directly: | |
459 | /// | |
460 | /// [`IntoIterator`]: trait.IntoIterator.html | |
461 | /// [`Iterator`]: trait.Iterator.html | |
462 | /// | |
463 | /// ``` | |
464 | /// let s1 = &[1, 2, 3]; | |
465 | /// let s2 = &[4, 5, 6]; | |
466 | /// | |
467 | /// let mut iter = s1.iter().zip(s2); | |
468 | /// | |
469 | /// assert_eq!(iter.next(), Some((&1, &4))); | |
470 | /// assert_eq!(iter.next(), Some((&2, &5))); | |
471 | /// assert_eq!(iter.next(), Some((&3, &6))); | |
472 | /// assert_eq!(iter.next(), None); | |
473 | /// ``` | |
474 | /// | |
475 | /// `zip()` is often used to zip an infinite iterator to a finite one. | |
476ff2be | 476 | /// This works because the finite iterator will eventually return [`None`], |
cc61c64b | 477 | /// ending the zipper. Zipping with `(0..)` can look a lot like [`enumerate`]: |
a7813a04 XL |
478 | /// |
479 | /// ``` | |
480 | /// let enumerate: Vec<_> = "foo".chars().enumerate().collect(); | |
481 | /// | |
482 | /// let zipper: Vec<_> = (0..).zip("foo".chars()).collect(); | |
483 | /// | |
484 | /// assert_eq!((0, 'f'), enumerate[0]); | |
485 | /// assert_eq!((0, 'f'), zipper[0]); | |
486 | /// | |
487 | /// assert_eq!((1, 'o'), enumerate[1]); | |
488 | /// assert_eq!((1, 'o'), zipper[1]); | |
489 | /// | |
490 | /// assert_eq!((2, 'o'), enumerate[2]); | |
491 | /// assert_eq!((2, 'o'), zipper[2]); | |
492 | /// ``` | |
493 | /// | |
cc61c64b XL |
494 | /// [`enumerate`]: trait.Iterator.html#method.enumerate |
495 | /// [`next`]: ../../std/iter/trait.Iterator.html#tymethod.next | |
476ff2be | 496 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
a7813a04 XL |
497 | #[inline] |
498 | #[stable(feature = "rust1", since = "1.0.0")] | |
499 | fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> where | |
500 | Self: Sized, U: IntoIterator | |
501 | { | |
3157f602 | 502 | Zip::new(self, other.into_iter()) |
a7813a04 XL |
503 | } |
504 | ||
505 | /// Takes a closure and creates an iterator which calls that closure on each | |
506 | /// element. | |
507 | /// | |
508 | /// `map()` transforms one iterator into another, by means of its argument: | |
a1dfa0c6 | 509 | /// something that implements [`FnMut`]. It produces a new iterator which |
a7813a04 XL |
510 | /// calls this closure on each element of the original iterator. |
511 | /// | |
512 | /// If you are good at thinking in types, you can think of `map()` like this: | |
513 | /// If you have an iterator that gives you elements of some type `A`, and | |
514 | /// you want an iterator of some other type `B`, you can use `map()`, | |
515 | /// passing a closure that takes an `A` and returns a `B`. | |
516 | /// | |
517 | /// `map()` is conceptually similar to a [`for`] loop. However, as `map()` is | |
518 | /// lazy, it is best used when you're already working with other iterators. | |
519 | /// If you're doing some sort of looping for a side effect, it's considered | |
520 | /// more idiomatic to use [`for`] than `map()`. | |
521 | /// | |
13cf67c4 | 522 | /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for |
a1dfa0c6 | 523 | /// [`FnMut`]: ../../std/ops/trait.FnMut.html |
a7813a04 XL |
524 | /// |
525 | /// # Examples | |
526 | /// | |
527 | /// Basic usage: | |
528 | /// | |
529 | /// ``` | |
530 | /// let a = [1, 2, 3]; | |
531 | /// | |
48663c56 | 532 | /// let mut iter = a.iter().map(|x| 2 * x); |
a7813a04 XL |
533 | /// |
534 | /// assert_eq!(iter.next(), Some(2)); | |
535 | /// assert_eq!(iter.next(), Some(4)); | |
536 | /// assert_eq!(iter.next(), Some(6)); | |
537 | /// assert_eq!(iter.next(), None); | |
538 | /// ``` | |
539 | /// | |
540 | /// If you're doing some sort of side effect, prefer [`for`] to `map()`: | |
541 | /// | |
542 | /// ``` | |
543 | /// # #![allow(unused_must_use)] | |
544 | /// // don't do this: | |
545 | /// (0..5).map(|x| println!("{}", x)); | |
546 | /// | |
547 | /// // it won't even execute, as it is lazy. Rust will warn you about this. | |
548 | /// | |
549 | /// // Instead, use for: | |
550 | /// for x in 0..5 { | |
551 | /// println!("{}", x); | |
552 | /// } | |
553 | /// ``` | |
554 | #[inline] | |
555 | #[stable(feature = "rust1", since = "1.0.0")] | |
556 | fn map<B, F>(self, f: F) -> Map<Self, F> where | |
557 | Self: Sized, F: FnMut(Self::Item) -> B, | |
558 | { | |
9fa01778 | 559 | Map::new(self, f) |
a7813a04 XL |
560 | } |
561 | ||
041b39d2 XL |
562 | /// Calls a closure on each element of an iterator. |
563 | /// | |
564 | /// This is equivalent to using a [`for`] loop on the iterator, although | |
9fa01778 | 565 | /// `break` and `continue` are not possible from a closure. It's generally |
041b39d2 | 566 | /// more idiomatic to use a `for` loop, but `for_each` may be more legible |
9fa01778 | 567 | /// when processing items at the end of longer iterator chains. In some |
041b39d2 XL |
568 | /// cases `for_each` may also be faster than a loop, because it will use |
569 | /// internal iteration on adaptors like `Chain`. | |
570 | /// | |
13cf67c4 | 571 | /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for |
041b39d2 XL |
572 | /// |
573 | /// # Examples | |
574 | /// | |
575 | /// Basic usage: | |
576 | /// | |
577 | /// ``` | |
041b39d2 XL |
578 | /// use std::sync::mpsc::channel; |
579 | /// | |
580 | /// let (tx, rx) = channel(); | |
581 | /// (0..5).map(|x| x * 2 + 1) | |
582 | /// .for_each(move |x| tx.send(x).unwrap()); | |
583 | /// | |
584 | /// let v: Vec<_> = rx.iter().collect(); | |
585 | /// assert_eq!(v, vec![1, 3, 5, 7, 9]); | |
586 | /// ``` | |
587 | /// | |
588 | /// For such a small example, a `for` loop may be cleaner, but `for_each` | |
589 | /// might be preferable to keep a functional style with longer iterators: | |
590 | /// | |
591 | /// ``` | |
041b39d2 XL |
592 | /// (0..5).flat_map(|x| x * 100 .. x * 110) |
593 | /// .enumerate() | |
594 | /// .filter(|&(i, x)| (i + x) % 3 == 0) | |
595 | /// .for_each(|(i, x)| println!("{}:{}", i, x)); | |
596 | /// ``` | |
597 | #[inline] | |
3b2f2976 | 598 | #[stable(feature = "iterator_for_each", since = "1.21.0")] |
041b39d2 XL |
599 | fn for_each<F>(self, mut f: F) where |
600 | Self: Sized, F: FnMut(Self::Item), | |
601 | { | |
602 | self.fold((), move |(), item| f(item)); | |
603 | } | |
604 | ||
a7813a04 XL |
605 | /// Creates an iterator which uses a closure to determine if an element |
606 | /// should be yielded. | |
607 | /// | |
608 | /// The closure must return `true` or `false`. `filter()` creates an | |
609 | /// iterator which calls this closure on each element. If the closure | |
610 | /// returns `true`, then the element is returned. If the closure returns | |
611 | /// `false`, it will try again, and call the closure on the next element, | |
612 | /// seeing if it passes the test. | |
613 | /// | |
614 | /// # Examples | |
615 | /// | |
616 | /// Basic usage: | |
617 | /// | |
618 | /// ``` | |
619 | /// let a = [0i32, 1, 2]; | |
620 | /// | |
48663c56 | 621 | /// let mut iter = a.iter().filter(|x| x.is_positive()); |
a7813a04 XL |
622 | /// |
623 | /// assert_eq!(iter.next(), Some(&1)); | |
624 | /// assert_eq!(iter.next(), Some(&2)); | |
625 | /// assert_eq!(iter.next(), None); | |
626 | /// ``` | |
627 | /// | |
628 | /// Because the closure passed to `filter()` takes a reference, and many | |
629 | /// iterators iterate over references, this leads to a possibly confusing | |
630 | /// situation, where the type of the closure is a double reference: | |
631 | /// | |
632 | /// ``` | |
633 | /// let a = [0, 1, 2]; | |
634 | /// | |
48663c56 | 635 | /// let mut iter = a.iter().filter(|x| **x > 1); // need two *s! |
a7813a04 XL |
636 | /// |
637 | /// assert_eq!(iter.next(), Some(&2)); | |
638 | /// assert_eq!(iter.next(), None); | |
639 | /// ``` | |
640 | /// | |
641 | /// It's common to instead use destructuring on the argument to strip away | |
642 | /// one: | |
643 | /// | |
644 | /// ``` | |
645 | /// let a = [0, 1, 2]; | |
646 | /// | |
48663c56 | 647 | /// let mut iter = a.iter().filter(|&x| *x > 1); // both & and * |
a7813a04 XL |
648 | /// |
649 | /// assert_eq!(iter.next(), Some(&2)); | |
650 | /// assert_eq!(iter.next(), None); | |
651 | /// ``` | |
652 | /// | |
653 | /// or both: | |
654 | /// | |
655 | /// ``` | |
656 | /// let a = [0, 1, 2]; | |
657 | /// | |
48663c56 | 658 | /// let mut iter = a.iter().filter(|&&x| x > 1); // two &s |
a7813a04 XL |
659 | /// |
660 | /// assert_eq!(iter.next(), Some(&2)); | |
661 | /// assert_eq!(iter.next(), None); | |
662 | /// ``` | |
663 | /// | |
664 | /// of these layers. | |
665 | #[inline] | |
666 | #[stable(feature = "rust1", since = "1.0.0")] | |
667 | fn filter<P>(self, predicate: P) -> Filter<Self, P> where | |
668 | Self: Sized, P: FnMut(&Self::Item) -> bool, | |
669 | { | |
9fa01778 | 670 | Filter::new(self, predicate) |
a7813a04 XL |
671 | } |
672 | ||
673 | /// Creates an iterator that both filters and maps. | |
674 | /// | |
cc61c64b | 675 | /// The closure must return an [`Option<T>`]. `filter_map` creates an |
a7813a04 | 676 | /// iterator which calls this closure on each element. If the closure |
476ff2be SL |
677 | /// returns [`Some(element)`][`Some`], then that element is returned. If the |
678 | /// closure returns [`None`], it will try again, and call the closure on the | |
679 | /// next element, seeing if it will return [`Some`]. | |
a7813a04 | 680 | /// |
3b2f2976 | 681 | /// Why `filter_map` and not just [`filter`] and [`map`]? The key is in this |
a7813a04 XL |
682 | /// part: |
683 | /// | |
cc61c64b XL |
684 | /// [`filter`]: #method.filter |
685 | /// [`map`]: #method.map | |
a7813a04 | 686 | /// |
476ff2be | 687 | /// > If the closure returns [`Some(element)`][`Some`], then that element is returned. |
a7813a04 XL |
688 | /// |
689 | /// In other words, it removes the [`Option<T>`] layer automatically. If your | |
690 | /// mapping is already returning an [`Option<T>`] and you want to skip over | |
cc61c64b | 691 | /// [`None`]s, then `filter_map` is much, much nicer to use. |
a7813a04 XL |
692 | /// |
693 | /// # Examples | |
694 | /// | |
695 | /// Basic usage: | |
696 | /// | |
697 | /// ``` | |
ff7c6d11 | 698 | /// let a = ["1", "lol", "3", "NaN", "5"]; |
a7813a04 XL |
699 | /// |
700 | /// let mut iter = a.iter().filter_map(|s| s.parse().ok()); | |
701 | /// | |
702 | /// assert_eq!(iter.next(), Some(1)); | |
ff7c6d11 XL |
703 | /// assert_eq!(iter.next(), Some(3)); |
704 | /// assert_eq!(iter.next(), Some(5)); | |
a7813a04 XL |
705 | /// assert_eq!(iter.next(), None); |
706 | /// ``` | |
707 | /// | |
cc61c64b | 708 | /// Here's the same example, but with [`filter`] and [`map`]: |
a7813a04 XL |
709 | /// |
710 | /// ``` | |
ff7c6d11 XL |
711 | /// let a = ["1", "lol", "3", "NaN", "5"]; |
712 | /// let mut iter = a.iter().map(|s| s.parse()).filter(|s| s.is_ok()).map(|s| s.unwrap()); | |
3b2f2976 | 713 | /// assert_eq!(iter.next(), Some(1)); |
ff7c6d11 XL |
714 | /// assert_eq!(iter.next(), Some(3)); |
715 | /// assert_eq!(iter.next(), Some(5)); | |
a7813a04 XL |
716 | /// assert_eq!(iter.next(), None); |
717 | /// ``` | |
718 | /// | |
476ff2be SL |
719 | /// [`Option<T>`]: ../../std/option/enum.Option.html |
720 | /// [`Some`]: ../../std/option/enum.Option.html#variant.Some | |
721 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
a7813a04 XL |
722 | #[inline] |
723 | #[stable(feature = "rust1", since = "1.0.0")] | |
724 | fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where | |
725 | Self: Sized, F: FnMut(Self::Item) -> Option<B>, | |
726 | { | |
9fa01778 | 727 | FilterMap::new(self, f) |
a7813a04 XL |
728 | } |
729 | ||
730 | /// Creates an iterator which gives the current iteration count as well as | |
731 | /// the next value. | |
732 | /// | |
733 | /// The iterator returned yields pairs `(i, val)`, where `i` is the | |
734 | /// current index of iteration and `val` is the value returned by the | |
735 | /// iterator. | |
736 | /// | |
737 | /// `enumerate()` keeps its count as a [`usize`]. If you want to count by a | |
cc61c64b | 738 | /// different sized integer, the [`zip`] function provides similar |
a7813a04 XL |
739 | /// functionality. |
740 | /// | |
a7813a04 XL |
741 | /// # Overflow Behavior |
742 | /// | |
743 | /// The method does no guarding against overflows, so enumerating more than | |
744 | /// [`usize::MAX`] elements either produces the wrong result or panics. If | |
745 | /// debug assertions are enabled, a panic is guaranteed. | |
746 | /// | |
a7813a04 XL |
747 | /// # Panics |
748 | /// | |
749 | /// The returned iterator might panic if the to-be-returned index would | |
476ff2be SL |
750 | /// overflow a [`usize`]. |
751 | /// | |
752 | /// [`usize::MAX`]: ../../std/usize/constant.MAX.html | |
753 | /// [`usize`]: ../../std/primitive.usize.html | |
cc61c64b | 754 | /// [`zip`]: #method.zip |
a7813a04 XL |
755 | /// |
756 | /// # Examples | |
757 | /// | |
758 | /// ``` | |
759 | /// let a = ['a', 'b', 'c']; | |
760 | /// | |
761 | /// let mut iter = a.iter().enumerate(); | |
762 | /// | |
763 | /// assert_eq!(iter.next(), Some((0, &'a'))); | |
764 | /// assert_eq!(iter.next(), Some((1, &'b'))); | |
765 | /// assert_eq!(iter.next(), Some((2, &'c'))); | |
766 | /// assert_eq!(iter.next(), None); | |
767 | /// ``` | |
768 | #[inline] | |
769 | #[stable(feature = "rust1", since = "1.0.0")] | |
770 | fn enumerate(self) -> Enumerate<Self> where Self: Sized { | |
9fa01778 | 771 | Enumerate::new(self) |
a7813a04 XL |
772 | } |
773 | ||
774 | /// Creates an iterator which can use `peek` to look at the next element of | |
775 | /// the iterator without consuming it. | |
776 | /// | |
cc61c64b | 777 | /// Adds a [`peek`] method to an iterator. See its documentation for |
a7813a04 XL |
778 | /// more information. |
779 | /// | |
cc61c64b | 780 | /// Note that the underlying iterator is still advanced when [`peek`] is |
a7813a04 | 781 | /// called for the first time: In order to retrieve the next element, |
7cac9316 XL |
782 | /// [`next`] is called on the underlying iterator, hence any side effects (i.e. |
783 | /// anything other than fetching the next value) of the [`next`] method | |
784 | /// will occur. | |
a7813a04 | 785 | /// |
cc61c64b XL |
786 | /// [`peek`]: struct.Peekable.html#method.peek |
787 | /// [`next`]: ../../std/iter/trait.Iterator.html#tymethod.next | |
a7813a04 XL |
788 | /// |
789 | /// # Examples | |
790 | /// | |
791 | /// Basic usage: | |
792 | /// | |
793 | /// ``` | |
794 | /// let xs = [1, 2, 3]; | |
795 | /// | |
796 | /// let mut iter = xs.iter().peekable(); | |
797 | /// | |
798 | /// // peek() lets us see into the future | |
799 | /// assert_eq!(iter.peek(), Some(&&1)); | |
800 | /// assert_eq!(iter.next(), Some(&1)); | |
801 | /// | |
802 | /// assert_eq!(iter.next(), Some(&2)); | |
803 | /// | |
804 | /// // we can peek() multiple times, the iterator won't advance | |
805 | /// assert_eq!(iter.peek(), Some(&&3)); | |
806 | /// assert_eq!(iter.peek(), Some(&&3)); | |
807 | /// | |
808 | /// assert_eq!(iter.next(), Some(&3)); | |
809 | /// | |
810 | /// // after the iterator is finished, so is peek() | |
811 | /// assert_eq!(iter.peek(), None); | |
812 | /// assert_eq!(iter.next(), None); | |
813 | /// ``` | |
814 | #[inline] | |
815 | #[stable(feature = "rust1", since = "1.0.0")] | |
816 | fn peekable(self) -> Peekable<Self> where Self: Sized { | |
9fa01778 | 817 | Peekable::new(self) |
a7813a04 XL |
818 | } |
819 | ||
cc61c64b | 820 | /// Creates an iterator that [`skip`]s elements based on a predicate. |
a7813a04 | 821 | /// |
cc61c64b | 822 | /// [`skip`]: #method.skip |
a7813a04 XL |
823 | /// |
824 | /// `skip_while()` takes a closure as an argument. It will call this | |
825 | /// closure on each element of the iterator, and ignore elements | |
826 | /// until it returns `false`. | |
827 | /// | |
828 | /// After `false` is returned, `skip_while()`'s job is over, and the | |
829 | /// rest of the elements are yielded. | |
830 | /// | |
831 | /// # Examples | |
832 | /// | |
833 | /// Basic usage: | |
834 | /// | |
835 | /// ``` | |
836 | /// let a = [-1i32, 0, 1]; | |
837 | /// | |
48663c56 | 838 | /// let mut iter = a.iter().skip_while(|x| x.is_negative()); |
a7813a04 XL |
839 | /// |
840 | /// assert_eq!(iter.next(), Some(&0)); | |
841 | /// assert_eq!(iter.next(), Some(&1)); | |
842 | /// assert_eq!(iter.next(), None); | |
843 | /// ``` | |
844 | /// | |
845 | /// Because the closure passed to `skip_while()` takes a reference, and many | |
846 | /// iterators iterate over references, this leads to a possibly confusing | |
847 | /// situation, where the type of the closure is a double reference: | |
848 | /// | |
849 | /// ``` | |
850 | /// let a = [-1, 0, 1]; | |
851 | /// | |
48663c56 | 852 | /// let mut iter = a.iter().skip_while(|x| **x < 0); // need two *s! |
a7813a04 XL |
853 | /// |
854 | /// assert_eq!(iter.next(), Some(&0)); | |
855 | /// assert_eq!(iter.next(), Some(&1)); | |
856 | /// assert_eq!(iter.next(), None); | |
857 | /// ``` | |
858 | /// | |
859 | /// Stopping after an initial `false`: | |
860 | /// | |
861 | /// ``` | |
862 | /// let a = [-1, 0, 1, -2]; | |
863 | /// | |
48663c56 | 864 | /// let mut iter = a.iter().skip_while(|x| **x < 0); |
a7813a04 XL |
865 | /// |
866 | /// assert_eq!(iter.next(), Some(&0)); | |
867 | /// assert_eq!(iter.next(), Some(&1)); | |
868 | /// | |
869 | /// // while this would have been false, since we already got a false, | |
870 | /// // skip_while() isn't used any more | |
871 | /// assert_eq!(iter.next(), Some(&-2)); | |
872 | /// | |
873 | /// assert_eq!(iter.next(), None); | |
874 | /// ``` | |
875 | #[inline] | |
876 | #[stable(feature = "rust1", since = "1.0.0")] | |
877 | fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where | |
878 | Self: Sized, P: FnMut(&Self::Item) -> bool, | |
879 | { | |
9fa01778 | 880 | SkipWhile::new(self, predicate) |
a7813a04 XL |
881 | } |
882 | ||
883 | /// Creates an iterator that yields elements based on a predicate. | |
884 | /// | |
885 | /// `take_while()` takes a closure as an argument. It will call this | |
886 | /// closure on each element of the iterator, and yield elements | |
887 | /// while it returns `true`. | |
888 | /// | |
889 | /// After `false` is returned, `take_while()`'s job is over, and the | |
890 | /// rest of the elements are ignored. | |
891 | /// | |
892 | /// # Examples | |
893 | /// | |
894 | /// Basic usage: | |
895 | /// | |
896 | /// ``` | |
897 | /// let a = [-1i32, 0, 1]; | |
898 | /// | |
48663c56 | 899 | /// let mut iter = a.iter().take_while(|x| x.is_negative()); |
a7813a04 XL |
900 | /// |
901 | /// assert_eq!(iter.next(), Some(&-1)); | |
902 | /// assert_eq!(iter.next(), None); | |
903 | /// ``` | |
904 | /// | |
905 | /// Because the closure passed to `take_while()` takes a reference, and many | |
906 | /// iterators iterate over references, this leads to a possibly confusing | |
907 | /// situation, where the type of the closure is a double reference: | |
908 | /// | |
909 | /// ``` | |
910 | /// let a = [-1, 0, 1]; | |
911 | /// | |
48663c56 | 912 | /// let mut iter = a.iter().take_while(|x| **x < 0); // need two *s! |
a7813a04 XL |
913 | /// |
914 | /// assert_eq!(iter.next(), Some(&-1)); | |
915 | /// assert_eq!(iter.next(), None); | |
916 | /// ``` | |
917 | /// | |
918 | /// Stopping after an initial `false`: | |
919 | /// | |
920 | /// ``` | |
921 | /// let a = [-1, 0, 1, -2]; | |
922 | /// | |
48663c56 | 923 | /// let mut iter = a.iter().take_while(|x| **x < 0); |
a7813a04 XL |
924 | /// |
925 | /// assert_eq!(iter.next(), Some(&-1)); | |
926 | /// | |
927 | /// // We have more elements that are less than zero, but since we already | |
928 | /// // got a false, take_while() isn't used any more | |
929 | /// assert_eq!(iter.next(), None); | |
930 | /// ``` | |
931 | /// | |
932 | /// Because `take_while()` needs to look at the value in order to see if it | |
933 | /// should be included or not, consuming iterators will see that it is | |
934 | /// removed: | |
935 | /// | |
936 | /// ``` | |
937 | /// let a = [1, 2, 3, 4]; | |
48663c56 | 938 | /// let mut iter = a.iter(); |
a7813a04 XL |
939 | /// |
940 | /// let result: Vec<i32> = iter.by_ref() | |
941 | /// .take_while(|n| **n != 3) | |
942 | /// .cloned() | |
943 | /// .collect(); | |
944 | /// | |
945 | /// assert_eq!(result, &[1, 2]); | |
946 | /// | |
947 | /// let result: Vec<i32> = iter.cloned().collect(); | |
948 | /// | |
949 | /// assert_eq!(result, &[4]); | |
950 | /// ``` | |
951 | /// | |
952 | /// The `3` is no longer there, because it was consumed in order to see if | |
9fa01778 | 953 | /// the iteration should stop, but wasn't placed back into the iterator. |
a7813a04 XL |
954 | #[inline] |
955 | #[stable(feature = "rust1", since = "1.0.0")] | |
956 | fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where | |
957 | Self: Sized, P: FnMut(&Self::Item) -> bool, | |
958 | { | |
9fa01778 | 959 | TakeWhile::new(self, predicate) |
a7813a04 XL |
960 | } |
961 | ||
962 | /// Creates an iterator that skips the first `n` elements. | |
963 | /// | |
964 | /// After they have been consumed, the rest of the elements are yielded. | |
dc9dc135 | 965 | /// Rather than overriding this method directly, instead override the `nth` method. |
a7813a04 XL |
966 | /// |
967 | /// # Examples | |
968 | /// | |
969 | /// Basic usage: | |
970 | /// | |
971 | /// ``` | |
972 | /// let a = [1, 2, 3]; | |
973 | /// | |
974 | /// let mut iter = a.iter().skip(2); | |
975 | /// | |
976 | /// assert_eq!(iter.next(), Some(&3)); | |
977 | /// assert_eq!(iter.next(), None); | |
978 | /// ``` | |
979 | #[inline] | |
980 | #[stable(feature = "rust1", since = "1.0.0")] | |
981 | fn skip(self, n: usize) -> Skip<Self> where Self: Sized { | |
9fa01778 | 982 | Skip::new(self, n) |
a7813a04 XL |
983 | } |
984 | ||
985 | /// Creates an iterator that yields its first `n` elements. | |
986 | /// | |
987 | /// # Examples | |
988 | /// | |
989 | /// Basic usage: | |
990 | /// | |
991 | /// ``` | |
992 | /// let a = [1, 2, 3]; | |
993 | /// | |
994 | /// let mut iter = a.iter().take(2); | |
995 | /// | |
996 | /// assert_eq!(iter.next(), Some(&1)); | |
997 | /// assert_eq!(iter.next(), Some(&2)); | |
998 | /// assert_eq!(iter.next(), None); | |
999 | /// ``` | |
1000 | /// | |
1001 | /// `take()` is often used with an infinite iterator, to make it finite: | |
1002 | /// | |
1003 | /// ``` | |
1004 | /// let mut iter = (0..).take(3); | |
1005 | /// | |
1006 | /// assert_eq!(iter.next(), Some(0)); | |
1007 | /// assert_eq!(iter.next(), Some(1)); | |
1008 | /// assert_eq!(iter.next(), Some(2)); | |
1009 | /// assert_eq!(iter.next(), None); | |
1010 | /// ``` | |
1011 | #[inline] | |
1012 | #[stable(feature = "rust1", since = "1.0.0")] | |
1013 | fn take(self, n: usize) -> Take<Self> where Self: Sized, { | |
9fa01778 | 1014 | Take::new(self, n) |
a7813a04 XL |
1015 | } |
1016 | ||
cc61c64b | 1017 | /// An iterator adaptor similar to [`fold`] that holds internal state and |
a7813a04 XL |
1018 | /// produces a new iterator. |
1019 | /// | |
cc61c64b | 1020 | /// [`fold`]: #method.fold |
a7813a04 XL |
1021 | /// |
1022 | /// `scan()` takes two arguments: an initial value which seeds the internal | |
1023 | /// state, and a closure with two arguments, the first being a mutable | |
1024 | /// reference to the internal state and the second an iterator element. | |
1025 | /// The closure can assign to the internal state to share state between | |
1026 | /// iterations. | |
1027 | /// | |
1028 | /// On iteration, the closure will be applied to each element of the | |
1029 | /// iterator and the return value from the closure, an [`Option`], is | |
1030 | /// yielded by the iterator. | |
1031 | /// | |
1032 | /// [`Option`]: ../../std/option/enum.Option.html | |
1033 | /// | |
1034 | /// # Examples | |
1035 | /// | |
1036 | /// Basic usage: | |
1037 | /// | |
1038 | /// ``` | |
1039 | /// let a = [1, 2, 3]; | |
1040 | /// | |
1041 | /// let mut iter = a.iter().scan(1, |state, &x| { | |
1042 | /// // each iteration, we'll multiply the state by the element | |
1043 | /// *state = *state * x; | |
1044 | /// | |
0531ce1d XL |
1045 | /// // then, we'll yield the negation of the state |
1046 | /// Some(-*state) | |
a7813a04 XL |
1047 | /// }); |
1048 | /// | |
0531ce1d XL |
1049 | /// assert_eq!(iter.next(), Some(-1)); |
1050 | /// assert_eq!(iter.next(), Some(-2)); | |
1051 | /// assert_eq!(iter.next(), Some(-6)); | |
a7813a04 XL |
1052 | /// assert_eq!(iter.next(), None); |
1053 | /// ``` | |
1054 | #[inline] | |
1055 | #[stable(feature = "rust1", since = "1.0.0")] | |
1056 | fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> | |
1057 | where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option<B>, | |
1058 | { | |
9fa01778 | 1059 | Scan::new(self, initial_state, f) |
a7813a04 XL |
1060 | } |
1061 | ||
1062 | /// Creates an iterator that works like map, but flattens nested structure. | |
1063 | /// | |
cc61c64b | 1064 | /// The [`map`] adapter is very useful, but only when the closure |
a7813a04 XL |
1065 | /// argument produces values. If it produces an iterator instead, there's |
1066 | /// an extra layer of indirection. `flat_map()` will remove this extra layer | |
1067 | /// on its own. | |
1068 | /// | |
83c7162d | 1069 | /// You can think of `flat_map(f)` as the semantic equivalent |
0531ce1d XL |
1070 | /// of [`map`]ping, and then [`flatten`]ing as in `map(f).flatten()`. |
1071 | /// | |
cc61c64b | 1072 | /// Another way of thinking about `flat_map()`: [`map`]'s closure returns |
a7813a04 XL |
1073 | /// one item for each element, and `flat_map()`'s closure returns an |
1074 | /// iterator for each element. | |
1075 | /// | |
cc61c64b | 1076 | /// [`map`]: #method.map |
0531ce1d | 1077 | /// [`flatten`]: #method.flatten |
476ff2be | 1078 | /// |
a7813a04 XL |
1079 | /// # Examples |
1080 | /// | |
1081 | /// Basic usage: | |
1082 | /// | |
1083 | /// ``` | |
1084 | /// let words = ["alpha", "beta", "gamma"]; | |
1085 | /// | |
1086 | /// // chars() returns an iterator | |
1087 | /// let merged: String = words.iter() | |
1088 | /// .flat_map(|s| s.chars()) | |
1089 | /// .collect(); | |
1090 | /// assert_eq!(merged, "alphabetagamma"); | |
1091 | /// ``` | |
1092 | #[inline] | |
1093 | #[stable(feature = "rust1", since = "1.0.0")] | |
1094 | fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> | |
1095 | where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U, | |
1096 | { | |
9fa01778 | 1097 | FlatMap::new(self, f) |
0531ce1d XL |
1098 | } |
1099 | ||
1100 | /// Creates an iterator that flattens nested structure. | |
1101 | /// | |
1102 | /// This is useful when you have an iterator of iterators or an iterator of | |
1103 | /// things that can be turned into iterators and you want to remove one | |
1104 | /// level of indirection. | |
1105 | /// | |
1106 | /// # Examples | |
1107 | /// | |
1108 | /// Basic usage: | |
1109 | /// | |
1110 | /// ``` | |
0531ce1d XL |
1111 | /// let data = vec![vec![1, 2, 3, 4], vec![5, 6]]; |
1112 | /// let flattened = data.into_iter().flatten().collect::<Vec<u8>>(); | |
1113 | /// assert_eq!(flattened, &[1, 2, 3, 4, 5, 6]); | |
1114 | /// ``` | |
1115 | /// | |
1116 | /// Mapping and then flattening: | |
1117 | /// | |
1118 | /// ``` | |
0531ce1d XL |
1119 | /// let words = ["alpha", "beta", "gamma"]; |
1120 | /// | |
1121 | /// // chars() returns an iterator | |
1122 | /// let merged: String = words.iter() | |
1123 | /// .map(|s| s.chars()) | |
1124 | /// .flatten() | |
1125 | /// .collect(); | |
1126 | /// assert_eq!(merged, "alphabetagamma"); | |
1127 | /// ``` | |
1128 | /// | |
1129 | /// You can also rewrite this in terms of [`flat_map()`], which is preferable | |
1130 | /// in this case since it conveys intent more clearly: | |
1131 | /// | |
1132 | /// ``` | |
1133 | /// let words = ["alpha", "beta", "gamma"]; | |
1134 | /// | |
1135 | /// // chars() returns an iterator | |
1136 | /// let merged: String = words.iter() | |
1137 | /// .flat_map(|s| s.chars()) | |
1138 | /// .collect(); | |
1139 | /// assert_eq!(merged, "alphabetagamma"); | |
1140 | /// ``` | |
1141 | /// | |
1142 | /// Flattening once only removes one level of nesting: | |
1143 | /// | |
1144 | /// ``` | |
0531ce1d XL |
1145 | /// let d3 = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]; |
1146 | /// | |
1147 | /// let d2 = d3.iter().flatten().collect::<Vec<_>>(); | |
1148 | /// assert_eq!(d2, [&[1, 2], &[3, 4], &[5, 6], &[7, 8]]); | |
1149 | /// | |
1150 | /// let d1 = d3.iter().flatten().flatten().collect::<Vec<_>>(); | |
1151 | /// assert_eq!(d1, [&1, &2, &3, &4, &5, &6, &7, &8]); | |
1152 | /// ``` | |
1153 | /// | |
1154 | /// Here we see that `flatten()` does not perform a "deep" flatten. | |
1155 | /// Instead, only one level of nesting is removed. That is, if you | |
1156 | /// `flatten()` a three-dimensional array the result will be | |
1157 | /// two-dimensional and not one-dimensional. To get a one-dimensional | |
1158 | /// structure, you have to `flatten()` again. | |
83c7162d XL |
1159 | /// |
1160 | /// [`flat_map()`]: #method.flat_map | |
0531ce1d | 1161 | #[inline] |
b7449926 | 1162 | #[stable(feature = "iterator_flatten", since = "1.29.0")] |
0531ce1d XL |
1163 | fn flatten(self) -> Flatten<Self> |
1164 | where Self: Sized, Self::Item: IntoIterator { | |
9fa01778 | 1165 | Flatten::new(self) |
a7813a04 XL |
1166 | } |
1167 | ||
476ff2be SL |
1168 | /// Creates an iterator which ends after the first [`None`]. |
1169 | /// | |
1170 | /// After an iterator returns [`None`], future calls may or may not yield | |
1171 | /// [`Some(T)`] again. `fuse()` adapts an iterator, ensuring that after a | |
1172 | /// [`None`] is given, it will always return [`None`] forever. | |
a7813a04 | 1173 | /// |
476ff2be SL |
1174 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
1175 | /// [`Some(T)`]: ../../std/option/enum.Option.html#variant.Some | |
a7813a04 XL |
1176 | /// |
1177 | /// # Examples | |
1178 | /// | |
1179 | /// Basic usage: | |
1180 | /// | |
1181 | /// ``` | |
1182 | /// // an iterator which alternates between Some and None | |
1183 | /// struct Alternate { | |
1184 | /// state: i32, | |
1185 | /// } | |
1186 | /// | |
1187 | /// impl Iterator for Alternate { | |
1188 | /// type Item = i32; | |
1189 | /// | |
1190 | /// fn next(&mut self) -> Option<i32> { | |
1191 | /// let val = self.state; | |
1192 | /// self.state = self.state + 1; | |
1193 | /// | |
1194 | /// // if it's even, Some(i32), else None | |
1195 | /// if val % 2 == 0 { | |
1196 | /// Some(val) | |
1197 | /// } else { | |
1198 | /// None | |
1199 | /// } | |
1200 | /// } | |
1201 | /// } | |
1202 | /// | |
1203 | /// let mut iter = Alternate { state: 0 }; | |
1204 | /// | |
1205 | /// // we can see our iterator going back and forth | |
1206 | /// assert_eq!(iter.next(), Some(0)); | |
1207 | /// assert_eq!(iter.next(), None); | |
1208 | /// assert_eq!(iter.next(), Some(2)); | |
1209 | /// assert_eq!(iter.next(), None); | |
1210 | /// | |
1211 | /// // however, once we fuse it... | |
1212 | /// let mut iter = iter.fuse(); | |
1213 | /// | |
1214 | /// assert_eq!(iter.next(), Some(4)); | |
1215 | /// assert_eq!(iter.next(), None); | |
1216 | /// | |
9fa01778 | 1217 | /// // it will always return `None` after the first time. |
a7813a04 XL |
1218 | /// assert_eq!(iter.next(), None); |
1219 | /// assert_eq!(iter.next(), None); | |
1220 | /// assert_eq!(iter.next(), None); | |
1221 | /// ``` | |
1222 | #[inline] | |
1223 | #[stable(feature = "rust1", since = "1.0.0")] | |
1224 | fn fuse(self) -> Fuse<Self> where Self: Sized { | |
9fa01778 | 1225 | Fuse::new(self) |
a7813a04 XL |
1226 | } |
1227 | ||
1228 | /// Do something with each element of an iterator, passing the value on. | |
1229 | /// | |
1230 | /// When using iterators, you'll often chain several of them together. | |
1231 | /// While working on such code, you might want to check out what's | |
1232 | /// happening at various parts in the pipeline. To do that, insert | |
1233 | /// a call to `inspect()`. | |
1234 | /// | |
94b46f34 XL |
1235 | /// It's more common for `inspect()` to be used as a debugging tool than to |
1236 | /// exist in your final code, but applications may find it useful in certain | |
1237 | /// situations when errors need to be logged before being discarded. | |
a7813a04 XL |
1238 | /// |
1239 | /// # Examples | |
1240 | /// | |
1241 | /// Basic usage: | |
1242 | /// | |
1243 | /// ``` | |
1244 | /// let a = [1, 4, 2, 3]; | |
1245 | /// | |
1246 | /// // this iterator sequence is complex. | |
1247 | /// let sum = a.iter() | |
0531ce1d XL |
1248 | /// .cloned() |
1249 | /// .filter(|x| x % 2 == 0) | |
1250 | /// .fold(0, |sum, i| sum + i); | |
a7813a04 XL |
1251 | /// |
1252 | /// println!("{}", sum); | |
1253 | /// | |
1254 | /// // let's add some inspect() calls to investigate what's happening | |
1255 | /// let sum = a.iter() | |
0531ce1d XL |
1256 | /// .cloned() |
1257 | /// .inspect(|x| println!("about to filter: {}", x)) | |
1258 | /// .filter(|x| x % 2 == 0) | |
1259 | /// .inspect(|x| println!("made it through filter: {}", x)) | |
1260 | /// .fold(0, |sum, i| sum + i); | |
a7813a04 XL |
1261 | /// |
1262 | /// println!("{}", sum); | |
1263 | /// ``` | |
1264 | /// | |
1265 | /// This will print: | |
1266 | /// | |
1267 | /// ```text | |
0531ce1d | 1268 | /// 6 |
a7813a04 XL |
1269 | /// about to filter: 1 |
1270 | /// about to filter: 4 | |
1271 | /// made it through filter: 4 | |
1272 | /// about to filter: 2 | |
1273 | /// made it through filter: 2 | |
1274 | /// about to filter: 3 | |
1275 | /// 6 | |
1276 | /// ``` | |
94b46f34 XL |
1277 | /// |
1278 | /// Logging errors before discarding them: | |
1279 | /// | |
1280 | /// ``` | |
1281 | /// let lines = ["1", "2", "a"]; | |
1282 | /// | |
1283 | /// let sum: i32 = lines | |
1284 | /// .iter() | |
1285 | /// .map(|line| line.parse::<i32>()) | |
1286 | /// .inspect(|num| { | |
1287 | /// if let Err(ref e) = *num { | |
1288 | /// println!("Parsing error: {}", e); | |
1289 | /// } | |
1290 | /// }) | |
1291 | /// .filter_map(Result::ok) | |
1292 | /// .sum(); | |
1293 | /// | |
1294 | /// println!("Sum: {}", sum); | |
1295 | /// ``` | |
1296 | /// | |
1297 | /// This will print: | |
1298 | /// | |
1299 | /// ```text | |
1300 | /// Parsing error: invalid digit found in string | |
1301 | /// Sum: 3 | |
1302 | /// ``` | |
a7813a04 XL |
1303 | #[inline] |
1304 | #[stable(feature = "rust1", since = "1.0.0")] | |
1305 | fn inspect<F>(self, f: F) -> Inspect<Self, F> where | |
1306 | Self: Sized, F: FnMut(&Self::Item), | |
1307 | { | |
9fa01778 | 1308 | Inspect::new(self, f) |
a7813a04 XL |
1309 | } |
1310 | ||
1311 | /// Borrows an iterator, rather than consuming it. | |
1312 | /// | |
1313 | /// This is useful to allow applying iterator adaptors while still | |
1314 | /// retaining ownership of the original iterator. | |
1315 | /// | |
1316 | /// # Examples | |
1317 | /// | |
1318 | /// Basic usage: | |
1319 | /// | |
1320 | /// ``` | |
1321 | /// let a = [1, 2, 3]; | |
1322 | /// | |
48663c56 | 1323 | /// let iter = a.iter(); |
a7813a04 | 1324 | /// |
0531ce1d | 1325 | /// let sum: i32 = iter.take(5).fold(0, |acc, i| acc + i ); |
a7813a04 XL |
1326 | /// |
1327 | /// assert_eq!(sum, 6); | |
1328 | /// | |
1329 | /// // if we try to use iter again, it won't work. The following line | |
1330 | /// // gives "error: use of moved value: `iter` | |
1331 | /// // assert_eq!(iter.next(), None); | |
1332 | /// | |
1333 | /// // let's try that again | |
1334 | /// let a = [1, 2, 3]; | |
1335 | /// | |
48663c56 | 1336 | /// let mut iter = a.iter(); |
a7813a04 XL |
1337 | /// |
1338 | /// // instead, we add in a .by_ref() | |
0531ce1d | 1339 | /// let sum: i32 = iter.by_ref().take(2).fold(0, |acc, i| acc + i ); |
a7813a04 XL |
1340 | /// |
1341 | /// assert_eq!(sum, 3); | |
1342 | /// | |
1343 | /// // now this is just fine: | |
1344 | /// assert_eq!(iter.next(), Some(&3)); | |
1345 | /// assert_eq!(iter.next(), None); | |
1346 | /// ``` | |
1347 | #[stable(feature = "rust1", since = "1.0.0")] | |
1348 | fn by_ref(&mut self) -> &mut Self where Self: Sized { self } | |
1349 | ||
1350 | /// Transforms an iterator into a collection. | |
1351 | /// | |
1352 | /// `collect()` can take anything iterable, and turn it into a relevant | |
1353 | /// collection. This is one of the more powerful methods in the standard | |
1354 | /// library, used in a variety of contexts. | |
1355 | /// | |
1356 | /// The most basic pattern in which `collect()` is used is to turn one | |
cc61c64b | 1357 | /// collection into another. You take a collection, call [`iter`] on it, |
a7813a04 XL |
1358 | /// do a bunch of transformations, and then `collect()` at the end. |
1359 | /// | |
1360 | /// One of the keys to `collect()`'s power is that many things you might | |
1361 | /// not think of as 'collections' actually are. For example, a [`String`] | |
32a655c1 SL |
1362 | /// is a collection of [`char`]s. And a collection of |
1363 | /// [`Result<T, E>`][`Result`] can be thought of as single | |
1364 | /// [`Result`]`<Collection<T>, E>`. See the examples below for more. | |
a7813a04 | 1365 | /// |
a7813a04 XL |
1366 | /// Because `collect()` is so general, it can cause problems with type |
1367 | /// inference. As such, `collect()` is one of the few times you'll see | |
1368 | /// the syntax affectionately known as the 'turbofish': `::<>`. This | |
1369 | /// helps the inference algorithm understand specifically which collection | |
1370 | /// you're trying to collect into. | |
1371 | /// | |
1372 | /// # Examples | |
1373 | /// | |
1374 | /// Basic usage: | |
1375 | /// | |
1376 | /// ``` | |
1377 | /// let a = [1, 2, 3]; | |
1378 | /// | |
1379 | /// let doubled: Vec<i32> = a.iter() | |
1380 | /// .map(|&x| x * 2) | |
1381 | /// .collect(); | |
1382 | /// | |
1383 | /// assert_eq!(vec![2, 4, 6], doubled); | |
1384 | /// ``` | |
1385 | /// | |
1386 | /// Note that we needed the `: Vec<i32>` on the left-hand side. This is because | |
1387 | /// we could collect into, for example, a [`VecDeque<T>`] instead: | |
1388 | /// | |
1389 | /// [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html | |
1390 | /// | |
1391 | /// ``` | |
1392 | /// use std::collections::VecDeque; | |
1393 | /// | |
1394 | /// let a = [1, 2, 3]; | |
1395 | /// | |
0531ce1d | 1396 | /// let doubled: VecDeque<i32> = a.iter().map(|&x| x * 2).collect(); |
a7813a04 XL |
1397 | /// |
1398 | /// assert_eq!(2, doubled[0]); | |
1399 | /// assert_eq!(4, doubled[1]); | |
1400 | /// assert_eq!(6, doubled[2]); | |
1401 | /// ``` | |
1402 | /// | |
1403 | /// Using the 'turbofish' instead of annotating `doubled`: | |
1404 | /// | |
1405 | /// ``` | |
1406 | /// let a = [1, 2, 3]; | |
1407 | /// | |
0531ce1d | 1408 | /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<i32>>(); |
a7813a04 XL |
1409 | /// |
1410 | /// assert_eq!(vec![2, 4, 6], doubled); | |
1411 | /// ``` | |
1412 | /// | |
3b2f2976 | 1413 | /// Because `collect()` only cares about what you're collecting into, you can |
a7813a04 XL |
1414 | /// still use a partial type hint, `_`, with the turbofish: |
1415 | /// | |
1416 | /// ``` | |
1417 | /// let a = [1, 2, 3]; | |
1418 | /// | |
0531ce1d | 1419 | /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<_>>(); |
a7813a04 XL |
1420 | /// |
1421 | /// assert_eq!(vec![2, 4, 6], doubled); | |
1422 | /// ``` | |
1423 | /// | |
1424 | /// Using `collect()` to make a [`String`]: | |
1425 | /// | |
1426 | /// ``` | |
1427 | /// let chars = ['g', 'd', 'k', 'k', 'n']; | |
1428 | /// | |
1429 | /// let hello: String = chars.iter() | |
0531ce1d XL |
1430 | /// .map(|&x| x as u8) |
1431 | /// .map(|x| (x + 1) as char) | |
1432 | /// .collect(); | |
a7813a04 XL |
1433 | /// |
1434 | /// assert_eq!("hello", hello); | |
1435 | /// ``` | |
1436 | /// | |
476ff2be | 1437 | /// If you have a list of [`Result<T, E>`][`Result`]s, you can use `collect()` to |
a7813a04 XL |
1438 | /// see if any of them failed: |
1439 | /// | |
1440 | /// ``` | |
1441 | /// let results = [Ok(1), Err("nope"), Ok(3), Err("bad")]; | |
1442 | /// | |
1443 | /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect(); | |
1444 | /// | |
1445 | /// // gives us the first error | |
1446 | /// assert_eq!(Err("nope"), result); | |
1447 | /// | |
1448 | /// let results = [Ok(1), Ok(3)]; | |
1449 | /// | |
1450 | /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect(); | |
1451 | /// | |
1452 | /// // gives us the list of answers | |
1453 | /// assert_eq!(Ok(vec![1, 3]), result); | |
1454 | /// ``` | |
476ff2be | 1455 | /// |
cc61c64b | 1456 | /// [`iter`]: ../../std/iter/trait.Iterator.html#tymethod.next |
476ff2be SL |
1457 | /// [`String`]: ../../std/string/struct.String.html |
1458 | /// [`char`]: ../../std/primitive.char.html | |
1459 | /// [`Result`]: ../../std/result/enum.Result.html | |
a7813a04 XL |
1460 | #[inline] |
1461 | #[stable(feature = "rust1", since = "1.0.0")] | |
83c7162d | 1462 | #[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"] |
a7813a04 XL |
1463 | fn collect<B: FromIterator<Self::Item>>(self) -> B where Self: Sized { |
1464 | FromIterator::from_iter(self) | |
1465 | } | |
1466 | ||
1467 | /// Consumes an iterator, creating two collections from it. | |
1468 | /// | |
1469 | /// The predicate passed to `partition()` can return `true`, or `false`. | |
1470 | /// `partition()` returns a pair, all of the elements for which it returned | |
1471 | /// `true`, and all of the elements for which it returned `false`. | |
1472 | /// | |
416331ca XL |
1473 | /// See also [`is_partitioned()`] and [`partition_in_place()`]. |
1474 | /// | |
1475 | /// [`is_partitioned()`]: #method.is_partitioned | |
1476 | /// [`partition_in_place()`]: #method.partition_in_place | |
1477 | /// | |
a7813a04 XL |
1478 | /// # Examples |
1479 | /// | |
1480 | /// Basic usage: | |
1481 | /// | |
1482 | /// ``` | |
1483 | /// let a = [1, 2, 3]; | |
1484 | /// | |
0531ce1d | 1485 | /// let (even, odd): (Vec<i32>, Vec<i32>) = a |
48663c56 | 1486 | /// .iter() |
0531ce1d | 1487 | /// .partition(|&n| n % 2 == 0); |
a7813a04 XL |
1488 | /// |
1489 | /// assert_eq!(even, vec![2]); | |
1490 | /// assert_eq!(odd, vec![1, 3]); | |
1491 | /// ``` | |
1492 | #[stable(feature = "rust1", since = "1.0.0")] | |
1493 | fn partition<B, F>(self, mut f: F) -> (B, B) where | |
1494 | Self: Sized, | |
1495 | B: Default + Extend<Self::Item>, | |
1496 | F: FnMut(&Self::Item) -> bool | |
1497 | { | |
1498 | let mut left: B = Default::default(); | |
1499 | let mut right: B = Default::default(); | |
1500 | ||
dc9dc135 | 1501 | self.for_each(|x| { |
a7813a04 XL |
1502 | if f(&x) { |
1503 | left.extend(Some(x)) | |
1504 | } else { | |
1505 | right.extend(Some(x)) | |
1506 | } | |
dc9dc135 | 1507 | }); |
a7813a04 XL |
1508 | |
1509 | (left, right) | |
1510 | } | |
1511 | ||
416331ca XL |
1512 | /// Reorder the elements of this iterator *in-place* according to the given predicate, |
1513 | /// such that all those that return `true` precede all those that return `false`. | |
1514 | /// Returns the number of `true` elements found. | |
1515 | /// | |
1516 | /// The relative order of partitioned items is not maintained. | |
1517 | /// | |
1518 | /// See also [`is_partitioned()`] and [`partition()`]. | |
1519 | /// | |
1520 | /// [`is_partitioned()`]: #method.is_partitioned | |
1521 | /// [`partition()`]: #method.partition | |
1522 | /// | |
1523 | /// # Examples | |
1524 | /// | |
1525 | /// ``` | |
1526 | /// #![feature(iter_partition_in_place)] | |
1527 | /// | |
1528 | /// let mut a = [1, 2, 3, 4, 5, 6, 7]; | |
1529 | /// | |
1530 | /// // Partition in-place between evens and odds | |
1531 | /// let i = a.iter_mut().partition_in_place(|&n| n % 2 == 0); | |
1532 | /// | |
1533 | /// assert_eq!(i, 3); | |
1534 | /// assert!(a[..i].iter().all(|&n| n % 2 == 0)); // evens | |
1535 | /// assert!(a[i..].iter().all(|&n| n % 2 == 1)); // odds | |
1536 | /// ``` | |
1537 | #[unstable(feature = "iter_partition_in_place", reason = "new API", issue = "62543")] | |
1538 | fn partition_in_place<'a, T: 'a, P>(mut self, ref mut predicate: P) -> usize | |
1539 | where | |
1540 | Self: Sized + DoubleEndedIterator<Item = &'a mut T>, | |
1541 | P: FnMut(&T) -> bool, | |
1542 | { | |
1543 | // FIXME: should we worry about the count overflowing? The only way to have more than | |
1544 | // `usize::MAX` mutable references is with ZSTs, which aren't useful to partition... | |
1545 | ||
1546 | // These closure "factory" functions exist to avoid genericity in `Self`. | |
1547 | ||
1548 | #[inline] | |
1549 | fn is_false<'a, T>( | |
1550 | predicate: &'a mut impl FnMut(&T) -> bool, | |
1551 | true_count: &'a mut usize, | |
1552 | ) -> impl FnMut(&&mut T) -> bool + 'a { | |
1553 | move |x| { | |
1554 | let p = predicate(&**x); | |
1555 | *true_count += p as usize; | |
1556 | !p | |
1557 | } | |
1558 | } | |
1559 | ||
1560 | #[inline] | |
1561 | fn is_true<T>( | |
1562 | predicate: &mut impl FnMut(&T) -> bool | |
1563 | ) -> impl FnMut(&&mut T) -> bool + '_ { | |
1564 | move |x| predicate(&**x) | |
1565 | } | |
1566 | ||
1567 | // Repeatedly find the first `false` and swap it with the last `true`. | |
1568 | let mut true_count = 0; | |
1569 | while let Some(head) = self.find(is_false(predicate, &mut true_count)) { | |
1570 | if let Some(tail) = self.rfind(is_true(predicate)) { | |
1571 | crate::mem::swap(head, tail); | |
1572 | true_count += 1; | |
1573 | } else { | |
1574 | break; | |
1575 | } | |
1576 | } | |
1577 | true_count | |
1578 | } | |
1579 | ||
1580 | /// Checks if the elements of this iterator are partitioned according to the given predicate, | |
1581 | /// such that all those that return `true` precede all those that return `false`. | |
1582 | /// | |
1583 | /// See also [`partition()`] and [`partition_in_place()`]. | |
1584 | /// | |
1585 | /// [`partition()`]: #method.partition | |
1586 | /// [`partition_in_place()`]: #method.partition_in_place | |
1587 | /// | |
1588 | /// # Examples | |
1589 | /// | |
1590 | /// ``` | |
1591 | /// #![feature(iter_is_partitioned)] | |
1592 | /// | |
1593 | /// assert!("Iterator".chars().is_partitioned(char::is_uppercase)); | |
1594 | /// assert!(!"IntoIterator".chars().is_partitioned(char::is_uppercase)); | |
1595 | /// ``` | |
1596 | #[unstable(feature = "iter_is_partitioned", reason = "new API", issue = "62544")] | |
1597 | fn is_partitioned<P>(mut self, mut predicate: P) -> bool | |
1598 | where | |
1599 | Self: Sized, | |
1600 | P: FnMut(Self::Item) -> bool, | |
1601 | { | |
1602 | // Either all items test `true`, or the first clause stops at `false` | |
1603 | // and we check that there are no more `true` items after that. | |
1604 | self.all(&mut predicate) || !self.any(predicate) | |
1605 | } | |
1606 | ||
abe05a73 XL |
1607 | /// An iterator method that applies a function as long as it returns |
1608 | /// successfully, producing a single, final value. | |
1609 | /// | |
1610 | /// `try_fold()` takes two arguments: an initial value, and a closure with | |
1611 | /// two arguments: an 'accumulator', and an element. The closure either | |
1612 | /// returns successfully, with the value that the accumulator should have | |
1613 | /// for the next iteration, or it returns failure, with an error value that | |
1614 | /// is propagated back to the caller immediately (short-circuiting). | |
1615 | /// | |
1616 | /// The initial value is the value the accumulator will have on the first | |
9fa01778 | 1617 | /// call. If applying the closure succeeded against every element of the |
abe05a73 XL |
1618 | /// iterator, `try_fold()` returns the final accumulator as success. |
1619 | /// | |
1620 | /// Folding is useful whenever you have a collection of something, and want | |
1621 | /// to produce a single value from it. | |
1622 | /// | |
1623 | /// # Note to Implementors | |
1624 | /// | |
1625 | /// Most of the other (forward) methods have default implementations in | |
1626 | /// terms of this one, so try to implement this explicitly if it can | |
1627 | /// do something better than the default `for` loop implementation. | |
1628 | /// | |
1629 | /// In particular, try to have this call `try_fold()` on the internal parts | |
9fa01778 | 1630 | /// from which this iterator is composed. If multiple calls are needed, |
0531ce1d XL |
1631 | /// the `?` operator may be convenient for chaining the accumulator value |
1632 | /// along, but beware any invariants that need to be upheld before those | |
9fa01778 | 1633 | /// early returns. This is a `&mut self` method, so iteration needs to be |
abe05a73 XL |
1634 | /// resumable after hitting an error here. |
1635 | /// | |
1636 | /// # Examples | |
1637 | /// | |
1638 | /// Basic usage: | |
1639 | /// | |
1640 | /// ``` | |
abe05a73 XL |
1641 | /// let a = [1, 2, 3]; |
1642 | /// | |
1643 | /// // the checked sum of all of the elements of the array | |
0531ce1d | 1644 | /// let sum = a.iter().try_fold(0i8, |acc, &x| acc.checked_add(x)); |
abe05a73 XL |
1645 | /// |
1646 | /// assert_eq!(sum, Some(6)); | |
1647 | /// ``` | |
1648 | /// | |
1649 | /// Short-circuiting: | |
1650 | /// | |
1651 | /// ``` | |
abe05a73 XL |
1652 | /// let a = [10, 20, 30, 100, 40, 50]; |
1653 | /// let mut it = a.iter(); | |
1654 | /// | |
1655 | /// // This sum overflows when adding the 100 element | |
1656 | /// let sum = it.try_fold(0i8, |acc, &x| acc.checked_add(x)); | |
1657 | /// assert_eq!(sum, None); | |
1658 | /// | |
1659 | /// // Because it short-circuited, the remaining elements are still | |
1660 | /// // available through the iterator. | |
1661 | /// assert_eq!(it.len(), 2); | |
1662 | /// assert_eq!(it.next(), Some(&40)); | |
1663 | /// ``` | |
1664 | #[inline] | |
83c7162d | 1665 | #[stable(feature = "iterator_try_fold", since = "1.27.0")] |
abe05a73 XL |
1666 | fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R where |
1667 | Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B> | |
1668 | { | |
1669 | let mut accum = init; | |
1670 | while let Some(x) = self.next() { | |
1671 | accum = f(accum, x)?; | |
1672 | } | |
1673 | Try::from_ok(accum) | |
1674 | } | |
1675 | ||
0531ce1d XL |
1676 | /// An iterator method that applies a fallible function to each item in the |
1677 | /// iterator, stopping at the first error and returning that error. | |
1678 | /// | |
1679 | /// This can also be thought of as the fallible form of [`for_each()`] | |
1680 | /// or as the stateless version of [`try_fold()`]. | |
1681 | /// | |
1682 | /// [`for_each()`]: #method.for_each | |
1683 | /// [`try_fold()`]: #method.try_fold | |
1684 | /// | |
1685 | /// # Examples | |
1686 | /// | |
1687 | /// ``` | |
0531ce1d XL |
1688 | /// use std::fs::rename; |
1689 | /// use std::io::{stdout, Write}; | |
1690 | /// use std::path::Path; | |
1691 | /// | |
1692 | /// let data = ["no_tea.txt", "stale_bread.json", "torrential_rain.png"]; | |
1693 | /// | |
1694 | /// let res = data.iter().try_for_each(|x| writeln!(stdout(), "{}", x)); | |
1695 | /// assert!(res.is_ok()); | |
1696 | /// | |
1697 | /// let mut it = data.iter().cloned(); | |
1698 | /// let res = it.try_for_each(|x| rename(x, Path::new(x).with_extension("old"))); | |
1699 | /// assert!(res.is_err()); | |
1700 | /// // It short-circuited, so the remaining items are still in the iterator: | |
1701 | /// assert_eq!(it.next(), Some("stale_bread.json")); | |
1702 | /// ``` | |
1703 | #[inline] | |
83c7162d | 1704 | #[stable(feature = "iterator_try_fold", since = "1.27.0")] |
0531ce1d XL |
1705 | fn try_for_each<F, R>(&mut self, mut f: F) -> R where |
1706 | Self: Sized, F: FnMut(Self::Item) -> R, R: Try<Ok=()> | |
1707 | { | |
1708 | self.try_fold((), move |(), x| f(x)) | |
1709 | } | |
1710 | ||
ea8adc8c | 1711 | /// An iterator method that applies a function, producing a single, final value. |
a7813a04 XL |
1712 | /// |
1713 | /// `fold()` takes two arguments: an initial value, and a closure with two | |
1714 | /// arguments: an 'accumulator', and an element. The closure returns the value that | |
1715 | /// the accumulator should have for the next iteration. | |
1716 | /// | |
1717 | /// The initial value is the value the accumulator will have on the first | |
1718 | /// call. | |
1719 | /// | |
1720 | /// After applying this closure to every element of the iterator, `fold()` | |
1721 | /// returns the accumulator. | |
1722 | /// | |
1723 | /// This operation is sometimes called 'reduce' or 'inject'. | |
1724 | /// | |
1725 | /// Folding is useful whenever you have a collection of something, and want | |
1726 | /// to produce a single value from it. | |
1727 | /// | |
2c00a5a8 XL |
1728 | /// Note: `fold()`, and similar methods that traverse the entire iterator, |
1729 | /// may not terminate for infinite iterators, even on traits for which a | |
1730 | /// result is determinable in finite time. | |
1731 | /// | |
a7813a04 XL |
1732 | /// # Examples |
1733 | /// | |
1734 | /// Basic usage: | |
1735 | /// | |
1736 | /// ``` | |
1737 | /// let a = [1, 2, 3]; | |
1738 | /// | |
abe05a73 | 1739 | /// // the sum of all of the elements of the array |
0531ce1d | 1740 | /// let sum = a.iter().fold(0, |acc, x| acc + x); |
a7813a04 XL |
1741 | /// |
1742 | /// assert_eq!(sum, 6); | |
1743 | /// ``` | |
1744 | /// | |
1745 | /// Let's walk through each step of the iteration here: | |
1746 | /// | |
1747 | /// | element | acc | x | result | | |
1748 | /// |---------|-----|---|--------| | |
1749 | /// | | 0 | | | | |
1750 | /// | 1 | 0 | 1 | 1 | | |
1751 | /// | 2 | 1 | 2 | 3 | | |
1752 | /// | 3 | 3 | 3 | 6 | | |
1753 | /// | |
1754 | /// And so, our final result, `6`. | |
1755 | /// | |
1756 | /// It's common for people who haven't used iterators a lot to | |
1757 | /// use a `for` loop with a list of things to build up a result. Those | |
1758 | /// can be turned into `fold()`s: | |
1759 | /// | |
13cf67c4 | 1760 | /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for |
476ff2be | 1761 | /// |
a7813a04 XL |
1762 | /// ``` |
1763 | /// let numbers = [1, 2, 3, 4, 5]; | |
1764 | /// | |
1765 | /// let mut result = 0; | |
1766 | /// | |
1767 | /// // for loop: | |
1768 | /// for i in &numbers { | |
1769 | /// result = result + i; | |
1770 | /// } | |
1771 | /// | |
1772 | /// // fold: | |
1773 | /// let result2 = numbers.iter().fold(0, |acc, &x| acc + x); | |
1774 | /// | |
1775 | /// // they're the same | |
1776 | /// assert_eq!(result, result2); | |
1777 | /// ``` | |
1778 | #[inline] | |
1779 | #[stable(feature = "rust1", since = "1.0.0")] | |
abe05a73 | 1780 | fn fold<B, F>(mut self, init: B, mut f: F) -> B where |
a7813a04 XL |
1781 | Self: Sized, F: FnMut(B, Self::Item) -> B, |
1782 | { | |
94b46f34 | 1783 | self.try_fold(init, move |acc, x| Ok::<B, !>(f(acc, x))).unwrap() |
a7813a04 XL |
1784 | } |
1785 | ||
1786 | /// Tests if every element of the iterator matches a predicate. | |
1787 | /// | |
1788 | /// `all()` takes a closure that returns `true` or `false`. It applies | |
1789 | /// this closure to each element of the iterator, and if they all return | |
1790 | /// `true`, then so does `all()`. If any of them return `false`, it | |
1791 | /// returns `false`. | |
1792 | /// | |
1793 | /// `all()` is short-circuiting; in other words, it will stop processing | |
1794 | /// as soon as it finds a `false`, given that no matter what else happens, | |
1795 | /// the result will also be `false`. | |
1796 | /// | |
1797 | /// An empty iterator returns `true`. | |
1798 | /// | |
1799 | /// # Examples | |
1800 | /// | |
1801 | /// Basic usage: | |
1802 | /// | |
1803 | /// ``` | |
1804 | /// let a = [1, 2, 3]; | |
1805 | /// | |
1806 | /// assert!(a.iter().all(|&x| x > 0)); | |
1807 | /// | |
1808 | /// assert!(!a.iter().all(|&x| x > 2)); | |
1809 | /// ``` | |
1810 | /// | |
1811 | /// Stopping at the first `false`: | |
1812 | /// | |
1813 | /// ``` | |
1814 | /// let a = [1, 2, 3]; | |
1815 | /// | |
1816 | /// let mut iter = a.iter(); | |
1817 | /// | |
1818 | /// assert!(!iter.all(|&x| x != 2)); | |
1819 | /// | |
1820 | /// // we can still use `iter`, as there are more elements. | |
1821 | /// assert_eq!(iter.next(), Some(&3)); | |
1822 | /// ``` | |
1823 | #[inline] | |
1824 | #[stable(feature = "rust1", since = "1.0.0")] | |
1825 | fn all<F>(&mut self, mut f: F) -> bool where | |
1826 | Self: Sized, F: FnMut(Self::Item) -> bool | |
1827 | { | |
0531ce1d | 1828 | self.try_for_each(move |x| { |
abe05a73 XL |
1829 | if f(x) { LoopState::Continue(()) } |
1830 | else { LoopState::Break(()) } | |
1831 | }) == LoopState::Continue(()) | |
a7813a04 XL |
1832 | } |
1833 | ||
1834 | /// Tests if any element of the iterator matches a predicate. | |
1835 | /// | |
1836 | /// `any()` takes a closure that returns `true` or `false`. It applies | |
1837 | /// this closure to each element of the iterator, and if any of them return | |
1838 | /// `true`, then so does `any()`. If they all return `false`, it | |
1839 | /// returns `false`. | |
1840 | /// | |
1841 | /// `any()` is short-circuiting; in other words, it will stop processing | |
1842 | /// as soon as it finds a `true`, given that no matter what else happens, | |
1843 | /// the result will also be `true`. | |
1844 | /// | |
1845 | /// An empty iterator returns `false`. | |
1846 | /// | |
1847 | /// # Examples | |
1848 | /// | |
1849 | /// Basic usage: | |
1850 | /// | |
1851 | /// ``` | |
1852 | /// let a = [1, 2, 3]; | |
1853 | /// | |
1854 | /// assert!(a.iter().any(|&x| x > 0)); | |
1855 | /// | |
1856 | /// assert!(!a.iter().any(|&x| x > 5)); | |
1857 | /// ``` | |
1858 | /// | |
1859 | /// Stopping at the first `true`: | |
1860 | /// | |
1861 | /// ``` | |
1862 | /// let a = [1, 2, 3]; | |
1863 | /// | |
1864 | /// let mut iter = a.iter(); | |
1865 | /// | |
1866 | /// assert!(iter.any(|&x| x != 2)); | |
1867 | /// | |
1868 | /// // we can still use `iter`, as there are more elements. | |
1869 | /// assert_eq!(iter.next(), Some(&2)); | |
1870 | /// ``` | |
1871 | #[inline] | |
1872 | #[stable(feature = "rust1", since = "1.0.0")] | |
1873 | fn any<F>(&mut self, mut f: F) -> bool where | |
1874 | Self: Sized, | |
1875 | F: FnMut(Self::Item) -> bool | |
1876 | { | |
0531ce1d | 1877 | self.try_for_each(move |x| { |
abe05a73 XL |
1878 | if f(x) { LoopState::Break(()) } |
1879 | else { LoopState::Continue(()) } | |
1880 | }) == LoopState::Break(()) | |
a7813a04 XL |
1881 | } |
1882 | ||
1883 | /// Searches for an element of an iterator that satisfies a predicate. | |
1884 | /// | |
1885 | /// `find()` takes a closure that returns `true` or `false`. It applies | |
1886 | /// this closure to each element of the iterator, and if any of them return | |
476ff2be SL |
1887 | /// `true`, then `find()` returns [`Some(element)`]. If they all return |
1888 | /// `false`, it returns [`None`]. | |
a7813a04 XL |
1889 | /// |
1890 | /// `find()` is short-circuiting; in other words, it will stop processing | |
1891 | /// as soon as the closure returns `true`. | |
1892 | /// | |
1893 | /// Because `find()` takes a reference, and many iterators iterate over | |
1894 | /// references, this leads to a possibly confusing situation where the | |
1895 | /// argument is a double reference. You can see this effect in the | |
1896 | /// examples below, with `&&x`. | |
1897 | /// | |
476ff2be SL |
1898 | /// [`Some(element)`]: ../../std/option/enum.Option.html#variant.Some |
1899 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
1900 | /// | |
a7813a04 XL |
1901 | /// # Examples |
1902 | /// | |
1903 | /// Basic usage: | |
1904 | /// | |
1905 | /// ``` | |
1906 | /// let a = [1, 2, 3]; | |
1907 | /// | |
1908 | /// assert_eq!(a.iter().find(|&&x| x == 2), Some(&2)); | |
1909 | /// | |
1910 | /// assert_eq!(a.iter().find(|&&x| x == 5), None); | |
1911 | /// ``` | |
1912 | /// | |
1913 | /// Stopping at the first `true`: | |
1914 | /// | |
1915 | /// ``` | |
1916 | /// let a = [1, 2, 3]; | |
1917 | /// | |
1918 | /// let mut iter = a.iter(); | |
1919 | /// | |
1920 | /// assert_eq!(iter.find(|&&x| x == 2), Some(&2)); | |
1921 | /// | |
1922 | /// // we can still use `iter`, as there are more elements. | |
1923 | /// assert_eq!(iter.next(), Some(&3)); | |
1924 | /// ``` | |
1925 | #[inline] | |
1926 | #[stable(feature = "rust1", since = "1.0.0")] | |
1927 | fn find<P>(&mut self, mut predicate: P) -> Option<Self::Item> where | |
1928 | Self: Sized, | |
1929 | P: FnMut(&Self::Item) -> bool, | |
1930 | { | |
0531ce1d | 1931 | self.try_for_each(move |x| { |
abe05a73 XL |
1932 | if predicate(&x) { LoopState::Break(x) } |
1933 | else { LoopState::Continue(()) } | |
1934 | }).break_value() | |
a7813a04 XL |
1935 | } |
1936 | ||
83c7162d XL |
1937 | /// Applies function to the elements of iterator and returns |
1938 | /// the first non-none result. | |
1939 | /// | |
1940 | /// `iter.find_map(f)` is equivalent to `iter.filter_map(f).next()`. | |
1941 | /// | |
1942 | /// | |
1943 | /// # Examples | |
1944 | /// | |
1945 | /// ``` | |
83c7162d XL |
1946 | /// let a = ["lol", "NaN", "2", "5"]; |
1947 | /// | |
a1dfa0c6 | 1948 | /// let first_number = a.iter().find_map(|s| s.parse().ok()); |
83c7162d XL |
1949 | /// |
1950 | /// assert_eq!(first_number, Some(2)); | |
1951 | /// ``` | |
1952 | #[inline] | |
b7449926 | 1953 | #[stable(feature = "iterator_find_map", since = "1.30.0")] |
83c7162d XL |
1954 | fn find_map<B, F>(&mut self, mut f: F) -> Option<B> where |
1955 | Self: Sized, | |
1956 | F: FnMut(Self::Item) -> Option<B>, | |
1957 | { | |
1958 | self.try_for_each(move |x| { | |
1959 | match f(x) { | |
1960 | Some(x) => LoopState::Break(x), | |
1961 | None => LoopState::Continue(()), | |
1962 | } | |
1963 | }).break_value() | |
1964 | } | |
1965 | ||
a7813a04 XL |
1966 | /// Searches for an element in an iterator, returning its index. |
1967 | /// | |
1968 | /// `position()` takes a closure that returns `true` or `false`. It applies | |
1969 | /// this closure to each element of the iterator, and if one of them | |
476ff2be SL |
1970 | /// returns `true`, then `position()` returns [`Some(index)`]. If all of |
1971 | /// them return `false`, it returns [`None`]. | |
a7813a04 XL |
1972 | /// |
1973 | /// `position()` is short-circuiting; in other words, it will stop | |
1974 | /// processing as soon as it finds a `true`. | |
1975 | /// | |
1976 | /// # Overflow Behavior | |
1977 | /// | |
1978 | /// The method does no guarding against overflows, so if there are more | |
476ff2be | 1979 | /// than [`usize::MAX`] non-matching elements, it either produces the wrong |
a7813a04 XL |
1980 | /// result or panics. If debug assertions are enabled, a panic is |
1981 | /// guaranteed. | |
1982 | /// | |
1983 | /// # Panics | |
1984 | /// | |
1985 | /// This function might panic if the iterator has more than `usize::MAX` | |
1986 | /// non-matching elements. | |
1987 | /// | |
476ff2be SL |
1988 | /// [`Some(index)`]: ../../std/option/enum.Option.html#variant.Some |
1989 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
1990 | /// [`usize::MAX`]: ../../std/usize/constant.MAX.html | |
1991 | /// | |
a7813a04 XL |
1992 | /// # Examples |
1993 | /// | |
1994 | /// Basic usage: | |
1995 | /// | |
1996 | /// ``` | |
1997 | /// let a = [1, 2, 3]; | |
1998 | /// | |
1999 | /// assert_eq!(a.iter().position(|&x| x == 2), Some(1)); | |
2000 | /// | |
2001 | /// assert_eq!(a.iter().position(|&x| x == 5), None); | |
2002 | /// ``` | |
2003 | /// | |
2004 | /// Stopping at the first `true`: | |
2005 | /// | |
2006 | /// ``` | |
cc61c64b | 2007 | /// let a = [1, 2, 3, 4]; |
a7813a04 XL |
2008 | /// |
2009 | /// let mut iter = a.iter(); | |
2010 | /// | |
cc61c64b | 2011 | /// assert_eq!(iter.position(|&x| x >= 2), Some(1)); |
a7813a04 XL |
2012 | /// |
2013 | /// // we can still use `iter`, as there are more elements. | |
2014 | /// assert_eq!(iter.next(), Some(&3)); | |
cc61c64b XL |
2015 | /// |
2016 | /// // The returned index depends on iterator state | |
2017 | /// assert_eq!(iter.position(|&x| x == 4), Some(0)); | |
2018 | /// | |
a7813a04 XL |
2019 | /// ``` |
2020 | #[inline] | |
abe05a73 | 2021 | #[rustc_inherit_overflow_checks] |
a7813a04 XL |
2022 | #[stable(feature = "rust1", since = "1.0.0")] |
2023 | fn position<P>(&mut self, mut predicate: P) -> Option<usize> where | |
2024 | Self: Sized, | |
2025 | P: FnMut(Self::Item) -> bool, | |
2026 | { | |
abe05a73 XL |
2027 | // The addition might panic on overflow |
2028 | self.try_fold(0, move |i, x| { | |
2029 | if predicate(x) { LoopState::Break(i) } | |
2030 | else { LoopState::Continue(i + 1) } | |
2031 | }).break_value() | |
a7813a04 XL |
2032 | } |
2033 | ||
2034 | /// Searches for an element in an iterator from the right, returning its | |
2035 | /// index. | |
2036 | /// | |
2037 | /// `rposition()` takes a closure that returns `true` or `false`. It applies | |
2038 | /// this closure to each element of the iterator, starting from the end, | |
2039 | /// and if one of them returns `true`, then `rposition()` returns | |
476ff2be | 2040 | /// [`Some(index)`]. If all of them return `false`, it returns [`None`]. |
a7813a04 XL |
2041 | /// |
2042 | /// `rposition()` is short-circuiting; in other words, it will stop | |
2043 | /// processing as soon as it finds a `true`. | |
2044 | /// | |
476ff2be SL |
2045 | /// [`Some(index)`]: ../../std/option/enum.Option.html#variant.Some |
2046 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
2047 | /// | |
a7813a04 XL |
2048 | /// # Examples |
2049 | /// | |
2050 | /// Basic usage: | |
2051 | /// | |
2052 | /// ``` | |
2053 | /// let a = [1, 2, 3]; | |
2054 | /// | |
2055 | /// assert_eq!(a.iter().rposition(|&x| x == 3), Some(2)); | |
2056 | /// | |
2057 | /// assert_eq!(a.iter().rposition(|&x| x == 5), None); | |
2058 | /// ``` | |
2059 | /// | |
2060 | /// Stopping at the first `true`: | |
2061 | /// | |
2062 | /// ``` | |
2063 | /// let a = [1, 2, 3]; | |
2064 | /// | |
2065 | /// let mut iter = a.iter(); | |
2066 | /// | |
2067 | /// assert_eq!(iter.rposition(|&x| x == 2), Some(1)); | |
2068 | /// | |
2069 | /// // we can still use `iter`, as there are more elements. | |
2070 | /// assert_eq!(iter.next(), Some(&1)); | |
2071 | /// ``` | |
2072 | #[inline] | |
2073 | #[stable(feature = "rust1", since = "1.0.0")] | |
2074 | fn rposition<P>(&mut self, mut predicate: P) -> Option<usize> where | |
2075 | P: FnMut(Self::Item) -> bool, | |
2076 | Self: Sized + ExactSizeIterator + DoubleEndedIterator | |
2077 | { | |
abe05a73 XL |
2078 | // No need for an overflow check here, because `ExactSizeIterator` |
2079 | // implies that the number of elements fits into a `usize`. | |
2080 | let n = self.len(); | |
2081 | self.try_rfold(n, move |i, x| { | |
2082 | let i = i - 1; | |
2083 | if predicate(x) { LoopState::Break(i) } | |
2084 | else { LoopState::Continue(i) } | |
2085 | }).break_value() | |
a7813a04 XL |
2086 | } |
2087 | ||
2088 | /// Returns the maximum element of an iterator. | |
2089 | /// | |
32a655c1 | 2090 | /// If several elements are equally maximum, the last element is |
8bb4bdeb XL |
2091 | /// returned. If the iterator is empty, [`None`] is returned. |
2092 | /// | |
2093 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
a7813a04 XL |
2094 | /// |
2095 | /// # Examples | |
2096 | /// | |
2097 | /// Basic usage: | |
2098 | /// | |
2099 | /// ``` | |
2100 | /// let a = [1, 2, 3]; | |
8bb4bdeb | 2101 | /// let b: Vec<u32> = Vec::new(); |
a7813a04 XL |
2102 | /// |
2103 | /// assert_eq!(a.iter().max(), Some(&3)); | |
8bb4bdeb | 2104 | /// assert_eq!(b.iter().max(), None); |
a7813a04 XL |
2105 | /// ``` |
2106 | #[inline] | |
2107 | #[stable(feature = "rust1", since = "1.0.0")] | |
2108 | fn max(self) -> Option<Self::Item> where Self: Sized, Self::Item: Ord | |
2109 | { | |
532ac7d7 | 2110 | self.max_by(Ord::cmp) |
a7813a04 XL |
2111 | } |
2112 | ||
2113 | /// Returns the minimum element of an iterator. | |
2114 | /// | |
32a655c1 | 2115 | /// If several elements are equally minimum, the first element is |
8bb4bdeb XL |
2116 | /// returned. If the iterator is empty, [`None`] is returned. |
2117 | /// | |
2118 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
a7813a04 XL |
2119 | /// |
2120 | /// # Examples | |
2121 | /// | |
2122 | /// Basic usage: | |
2123 | /// | |
2124 | /// ``` | |
2125 | /// let a = [1, 2, 3]; | |
8bb4bdeb | 2126 | /// let b: Vec<u32> = Vec::new(); |
a7813a04 XL |
2127 | /// |
2128 | /// assert_eq!(a.iter().min(), Some(&1)); | |
8bb4bdeb | 2129 | /// assert_eq!(b.iter().min(), None); |
a7813a04 XL |
2130 | /// ``` |
2131 | #[inline] | |
2132 | #[stable(feature = "rust1", since = "1.0.0")] | |
2133 | fn min(self) -> Option<Self::Item> where Self: Sized, Self::Item: Ord | |
2134 | { | |
532ac7d7 | 2135 | self.min_by(Ord::cmp) |
a7813a04 XL |
2136 | } |
2137 | ||
2138 | /// Returns the element that gives the maximum value from the | |
2139 | /// specified function. | |
2140 | /// | |
32a655c1 | 2141 | /// If several elements are equally maximum, the last element is |
8bb4bdeb XL |
2142 | /// returned. If the iterator is empty, [`None`] is returned. |
2143 | /// | |
2144 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
a7813a04 XL |
2145 | /// |
2146 | /// # Examples | |
2147 | /// | |
2148 | /// ``` | |
2149 | /// let a = [-3_i32, 0, 1, 5, -10]; | |
2150 | /// assert_eq!(*a.iter().max_by_key(|x| x.abs()).unwrap(), -10); | |
2151 | /// ``` | |
2152 | #[inline] | |
2153 | #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] | |
532ac7d7 | 2154 | fn max_by_key<B: Ord, F>(self, mut f: F) -> Option<Self::Item> |
a7813a04 XL |
2155 | where Self: Sized, F: FnMut(&Self::Item) -> B, |
2156 | { | |
532ac7d7 XL |
2157 | // switch to y even if it is only equal, to preserve stability. |
2158 | select_fold1(self.map(|x| (f(&x), x)), |(x_p, _), (y_p, _)| x_p <= y_p).map(|(_, x)| x) | |
a7813a04 XL |
2159 | } |
2160 | ||
9e0c209e SL |
2161 | /// Returns the element that gives the maximum value with respect to the |
2162 | /// specified comparison function. | |
2163 | /// | |
32a655c1 | 2164 | /// If several elements are equally maximum, the last element is |
8bb4bdeb XL |
2165 | /// returned. If the iterator is empty, [`None`] is returned. |
2166 | /// | |
2167 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
9e0c209e SL |
2168 | /// |
2169 | /// # Examples | |
2170 | /// | |
2171 | /// ``` | |
9e0c209e SL |
2172 | /// let a = [-3_i32, 0, 1, 5, -10]; |
2173 | /// assert_eq!(*a.iter().max_by(|x, y| x.cmp(y)).unwrap(), 5); | |
2174 | /// ``` | |
2175 | #[inline] | |
476ff2be | 2176 | #[stable(feature = "iter_max_by", since = "1.15.0")] |
9e0c209e SL |
2177 | fn max_by<F>(self, mut compare: F) -> Option<Self::Item> |
2178 | where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering, | |
2179 | { | |
532ac7d7 XL |
2180 | // switch to y even if it is only equal, to preserve stability. |
2181 | select_fold1(self, |x, y| compare(x, y) != Ordering::Greater) | |
9e0c209e SL |
2182 | } |
2183 | ||
a7813a04 XL |
2184 | /// Returns the element that gives the minimum value from the |
2185 | /// specified function. | |
2186 | /// | |
32a655c1 | 2187 | /// If several elements are equally minimum, the first element is |
8bb4bdeb XL |
2188 | /// returned. If the iterator is empty, [`None`] is returned. |
2189 | /// | |
2190 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
a7813a04 XL |
2191 | /// |
2192 | /// # Examples | |
2193 | /// | |
2194 | /// ``` | |
2195 | /// let a = [-3_i32, 0, 1, 5, -10]; | |
2196 | /// assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0); | |
2197 | /// ``` | |
2198 | #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] | |
532ac7d7 | 2199 | fn min_by_key<B: Ord, F>(self, mut f: F) -> Option<Self::Item> |
a7813a04 XL |
2200 | where Self: Sized, F: FnMut(&Self::Item) -> B, |
2201 | { | |
532ac7d7 XL |
2202 | // only switch to y if it is strictly smaller, to preserve stability. |
2203 | select_fold1(self.map(|x| (f(&x), x)), |(x_p, _), (y_p, _)| x_p > y_p).map(|(_, x)| x) | |
a7813a04 XL |
2204 | } |
2205 | ||
9e0c209e SL |
2206 | /// Returns the element that gives the minimum value with respect to the |
2207 | /// specified comparison function. | |
2208 | /// | |
32a655c1 | 2209 | /// If several elements are equally minimum, the first element is |
8bb4bdeb XL |
2210 | /// returned. If the iterator is empty, [`None`] is returned. |
2211 | /// | |
2212 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
9e0c209e SL |
2213 | /// |
2214 | /// # Examples | |
2215 | /// | |
2216 | /// ``` | |
9e0c209e SL |
2217 | /// let a = [-3_i32, 0, 1, 5, -10]; |
2218 | /// assert_eq!(*a.iter().min_by(|x, y| x.cmp(y)).unwrap(), -10); | |
2219 | /// ``` | |
2220 | #[inline] | |
476ff2be | 2221 | #[stable(feature = "iter_min_by", since = "1.15.0")] |
9e0c209e SL |
2222 | fn min_by<F>(self, mut compare: F) -> Option<Self::Item> |
2223 | where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering, | |
2224 | { | |
532ac7d7 XL |
2225 | // only switch to y if it is strictly smaller, to preserve stability. |
2226 | select_fold1(self, |x, y| compare(x, y) == Ordering::Greater) | |
9e0c209e SL |
2227 | } |
2228 | ||
2229 | ||
a7813a04 XL |
2230 | /// Reverses an iterator's direction. |
2231 | /// | |
2232 | /// Usually, iterators iterate from left to right. After using `rev()`, | |
2233 | /// an iterator will instead iterate from right to left. | |
2234 | /// | |
2235 | /// This is only possible if the iterator has an end, so `rev()` only | |
2236 | /// works on [`DoubleEndedIterator`]s. | |
2237 | /// | |
2238 | /// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html | |
2239 | /// | |
2240 | /// # Examples | |
2241 | /// | |
2242 | /// ``` | |
2243 | /// let a = [1, 2, 3]; | |
2244 | /// | |
2245 | /// let mut iter = a.iter().rev(); | |
2246 | /// | |
2247 | /// assert_eq!(iter.next(), Some(&3)); | |
2248 | /// assert_eq!(iter.next(), Some(&2)); | |
2249 | /// assert_eq!(iter.next(), Some(&1)); | |
2250 | /// | |
2251 | /// assert_eq!(iter.next(), None); | |
2252 | /// ``` | |
2253 | #[inline] | |
2254 | #[stable(feature = "rust1", since = "1.0.0")] | |
2255 | fn rev(self) -> Rev<Self> where Self: Sized + DoubleEndedIterator { | |
9fa01778 | 2256 | Rev::new(self) |
a7813a04 XL |
2257 | } |
2258 | ||
2259 | /// Converts an iterator of pairs into a pair of containers. | |
2260 | /// | |
2261 | /// `unzip()` consumes an entire iterator of pairs, producing two | |
2262 | /// collections: one from the left elements of the pairs, and one | |
2263 | /// from the right elements. | |
2264 | /// | |
cc61c64b | 2265 | /// This function is, in some sense, the opposite of [`zip`]. |
a7813a04 | 2266 | /// |
cc61c64b | 2267 | /// [`zip`]: #method.zip |
a7813a04 XL |
2268 | /// |
2269 | /// # Examples | |
2270 | /// | |
2271 | /// Basic usage: | |
2272 | /// | |
2273 | /// ``` | |
2274 | /// let a = [(1, 2), (3, 4)]; | |
2275 | /// | |
2276 | /// let (left, right): (Vec<_>, Vec<_>) = a.iter().cloned().unzip(); | |
2277 | /// | |
2278 | /// assert_eq!(left, [1, 3]); | |
2279 | /// assert_eq!(right, [2, 4]); | |
2280 | /// ``` | |
2281 | #[stable(feature = "rust1", since = "1.0.0")] | |
2282 | fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where | |
2283 | FromA: Default + Extend<A>, | |
2284 | FromB: Default + Extend<B>, | |
2285 | Self: Sized + Iterator<Item=(A, B)>, | |
2286 | { | |
a7813a04 XL |
2287 | let mut ts: FromA = Default::default(); |
2288 | let mut us: FromB = Default::default(); | |
2289 | ||
abe05a73 | 2290 | self.for_each(|(t, u)| { |
a7813a04 XL |
2291 | ts.extend(Some(t)); |
2292 | us.extend(Some(u)); | |
abe05a73 | 2293 | }); |
a7813a04 XL |
2294 | |
2295 | (ts, us) | |
2296 | } | |
2297 | ||
0731742a XL |
2298 | /// Creates an iterator which copies all of its elements. |
2299 | /// | |
2300 | /// This is useful when you have an iterator over `&T`, but you need an | |
2301 | /// iterator over `T`. | |
2302 | /// | |
2303 | /// # Examples | |
2304 | /// | |
2305 | /// Basic usage: | |
2306 | /// | |
2307 | /// ``` | |
0731742a XL |
2308 | /// let a = [1, 2, 3]; |
2309 | /// | |
2310 | /// let v_cloned: Vec<_> = a.iter().copied().collect(); | |
2311 | /// | |
2312 | /// // copied is the same as .map(|&x| x) | |
2313 | /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); | |
2314 | /// | |
2315 | /// assert_eq!(v_cloned, vec![1, 2, 3]); | |
2316 | /// assert_eq!(v_map, vec![1, 2, 3]); | |
2317 | /// ``` | |
48663c56 | 2318 | #[stable(feature = "iter_copied", since = "1.36.0")] |
0731742a XL |
2319 | fn copied<'a, T: 'a>(self) -> Copied<Self> |
2320 | where Self: Sized + Iterator<Item=&'a T>, T: Copy | |
2321 | { | |
9fa01778 | 2322 | Copied::new(self) |
0731742a XL |
2323 | } |
2324 | ||
cc61c64b | 2325 | /// Creates an iterator which [`clone`]s all of its elements. |
a7813a04 XL |
2326 | /// |
2327 | /// This is useful when you have an iterator over `&T`, but you need an | |
2328 | /// iterator over `T`. | |
2329 | /// | |
cc61c64b | 2330 | /// [`clone`]: ../../std/clone/trait.Clone.html#tymethod.clone |
476ff2be | 2331 | /// |
a7813a04 XL |
2332 | /// # Examples |
2333 | /// | |
2334 | /// Basic usage: | |
2335 | /// | |
2336 | /// ``` | |
2337 | /// let a = [1, 2, 3]; | |
2338 | /// | |
2339 | /// let v_cloned: Vec<_> = a.iter().cloned().collect(); | |
2340 | /// | |
2341 | /// // cloned is the same as .map(|&x| x), for integers | |
2342 | /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); | |
2343 | /// | |
2344 | /// assert_eq!(v_cloned, vec![1, 2, 3]); | |
2345 | /// assert_eq!(v_map, vec![1, 2, 3]); | |
2346 | /// ``` | |
2347 | #[stable(feature = "rust1", since = "1.0.0")] | |
2348 | fn cloned<'a, T: 'a>(self) -> Cloned<Self> | |
2349 | where Self: Sized + Iterator<Item=&'a T>, T: Clone | |
2350 | { | |
9fa01778 | 2351 | Cloned::new(self) |
a7813a04 XL |
2352 | } |
2353 | ||
2354 | /// Repeats an iterator endlessly. | |
2355 | /// | |
476ff2be | 2356 | /// Instead of stopping at [`None`], the iterator will instead start again, |
a7813a04 XL |
2357 | /// from the beginning. After iterating again, it will start at the |
2358 | /// beginning again. And again. And again. Forever. | |
2359 | /// | |
476ff2be SL |
2360 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
2361 | /// | |
a7813a04 XL |
2362 | /// # Examples |
2363 | /// | |
2364 | /// Basic usage: | |
2365 | /// | |
2366 | /// ``` | |
2367 | /// let a = [1, 2, 3]; | |
2368 | /// | |
2369 | /// let mut it = a.iter().cycle(); | |
2370 | /// | |
2371 | /// assert_eq!(it.next(), Some(&1)); | |
2372 | /// assert_eq!(it.next(), Some(&2)); | |
2373 | /// assert_eq!(it.next(), Some(&3)); | |
2374 | /// assert_eq!(it.next(), Some(&1)); | |
2375 | /// assert_eq!(it.next(), Some(&2)); | |
2376 | /// assert_eq!(it.next(), Some(&3)); | |
2377 | /// assert_eq!(it.next(), Some(&1)); | |
2378 | /// ``` | |
2379 | #[stable(feature = "rust1", since = "1.0.0")] | |
2380 | #[inline] | |
2381 | fn cycle(self) -> Cycle<Self> where Self: Sized + Clone { | |
9fa01778 | 2382 | Cycle::new(self) |
a7813a04 XL |
2383 | } |
2384 | ||
2385 | /// Sums the elements of an iterator. | |
2386 | /// | |
2387 | /// Takes each element, adds them together, and returns the result. | |
2388 | /// | |
2389 | /// An empty iterator returns the zero value of the type. | |
2390 | /// | |
3157f602 XL |
2391 | /// # Panics |
2392 | /// | |
476ff2be | 2393 | /// When calling `sum()` and a primitive integer type is being returned, this |
9e0c209e SL |
2394 | /// method will panic if the computation overflows and debug assertions are |
2395 | /// enabled. | |
3157f602 | 2396 | /// |
a7813a04 XL |
2397 | /// # Examples |
2398 | /// | |
2399 | /// Basic usage: | |
2400 | /// | |
2401 | /// ``` | |
a7813a04 XL |
2402 | /// let a = [1, 2, 3]; |
2403 | /// let sum: i32 = a.iter().sum(); | |
2404 | /// | |
2405 | /// assert_eq!(sum, 6); | |
2406 | /// ``` | |
3157f602 XL |
2407 | #[stable(feature = "iter_arith", since = "1.11.0")] |
2408 | fn sum<S>(self) -> S | |
2409 | where Self: Sized, | |
2410 | S: Sum<Self::Item>, | |
a7813a04 | 2411 | { |
3157f602 | 2412 | Sum::sum(self) |
a7813a04 XL |
2413 | } |
2414 | ||
2415 | /// Iterates over the entire iterator, multiplying all the elements | |
2416 | /// | |
2417 | /// An empty iterator returns the one value of the type. | |
2418 | /// | |
3157f602 XL |
2419 | /// # Panics |
2420 | /// | |
476ff2be | 2421 | /// When calling `product()` and a primitive integer type is being returned, |
9e0c209e SL |
2422 | /// method will panic if the computation overflows and debug assertions are |
2423 | /// enabled. | |
3157f602 | 2424 | /// |
a7813a04 XL |
2425 | /// # Examples |
2426 | /// | |
2427 | /// ``` | |
a7813a04 | 2428 | /// fn factorial(n: u32) -> u32 { |
0731742a | 2429 | /// (1..=n).product() |
a7813a04 XL |
2430 | /// } |
2431 | /// assert_eq!(factorial(0), 1); | |
2432 | /// assert_eq!(factorial(1), 1); | |
2433 | /// assert_eq!(factorial(5), 120); | |
2434 | /// ``` | |
3157f602 XL |
2435 | #[stable(feature = "iter_arith", since = "1.11.0")] |
2436 | fn product<P>(self) -> P | |
2437 | where Self: Sized, | |
2438 | P: Product<Self::Item>, | |
a7813a04 | 2439 | { |
3157f602 | 2440 | Product::product(self) |
a7813a04 XL |
2441 | } |
2442 | ||
2443 | /// Lexicographically compares the elements of this `Iterator` with those | |
2444 | /// of another. | |
2445 | #[stable(feature = "iter_order", since = "1.5.0")] | |
2446 | fn cmp<I>(mut self, other: I) -> Ordering where | |
2447 | I: IntoIterator<Item = Self::Item>, | |
2448 | Self::Item: Ord, | |
2449 | Self: Sized, | |
2450 | { | |
2451 | let mut other = other.into_iter(); | |
2452 | ||
2453 | loop { | |
abe05a73 XL |
2454 | let x = match self.next() { |
2455 | None => if other.next().is_none() { | |
2456 | return Ordering::Equal | |
2457 | } else { | |
2458 | return Ordering::Less | |
a7813a04 | 2459 | }, |
abe05a73 XL |
2460 | Some(val) => val, |
2461 | }; | |
2462 | ||
2463 | let y = match other.next() { | |
2464 | None => return Ordering::Greater, | |
2465 | Some(val) => val, | |
2466 | }; | |
2467 | ||
2468 | match x.cmp(&y) { | |
2469 | Ordering::Equal => (), | |
2470 | non_eq => return non_eq, | |
a7813a04 XL |
2471 | } |
2472 | } | |
2473 | } | |
2474 | ||
2475 | /// Lexicographically compares the elements of this `Iterator` with those | |
2476 | /// of another. | |
2477 | #[stable(feature = "iter_order", since = "1.5.0")] | |
2478 | fn partial_cmp<I>(mut self, other: I) -> Option<Ordering> where | |
2479 | I: IntoIterator, | |
2480 | Self::Item: PartialOrd<I::Item>, | |
2481 | Self: Sized, | |
2482 | { | |
2483 | let mut other = other.into_iter(); | |
2484 | ||
2485 | loop { | |
abe05a73 XL |
2486 | let x = match self.next() { |
2487 | None => if other.next().is_none() { | |
2488 | return Some(Ordering::Equal) | |
2489 | } else { | |
2490 | return Some(Ordering::Less) | |
a7813a04 | 2491 | }, |
abe05a73 XL |
2492 | Some(val) => val, |
2493 | }; | |
2494 | ||
2495 | let y = match other.next() { | |
2496 | None => return Some(Ordering::Greater), | |
2497 | Some(val) => val, | |
2498 | }; | |
2499 | ||
2500 | match x.partial_cmp(&y) { | |
2501 | Some(Ordering::Equal) => (), | |
2502 | non_eq => return non_eq, | |
a7813a04 XL |
2503 | } |
2504 | } | |
2505 | } | |
2506 | ||
2507 | /// Determines if the elements of this `Iterator` are equal to those of | |
2508 | /// another. | |
2509 | #[stable(feature = "iter_order", since = "1.5.0")] | |
2510 | fn eq<I>(mut self, other: I) -> bool where | |
2511 | I: IntoIterator, | |
2512 | Self::Item: PartialEq<I::Item>, | |
2513 | Self: Sized, | |
2514 | { | |
2515 | let mut other = other.into_iter(); | |
2516 | ||
2517 | loop { | |
abe05a73 XL |
2518 | let x = match self.next() { |
2519 | None => return other.next().is_none(), | |
2520 | Some(val) => val, | |
2521 | }; | |
2522 | ||
2523 | let y = match other.next() { | |
2524 | None => return false, | |
2525 | Some(val) => val, | |
2526 | }; | |
2527 | ||
2528 | if x != y { return false } | |
a7813a04 XL |
2529 | } |
2530 | } | |
2531 | ||
2532 | /// Determines if the elements of this `Iterator` are unequal to those of | |
2533 | /// another. | |
2534 | #[stable(feature = "iter_order", since = "1.5.0")] | |
532ac7d7 | 2535 | fn ne<I>(self, other: I) -> bool where |
a7813a04 XL |
2536 | I: IntoIterator, |
2537 | Self::Item: PartialEq<I::Item>, | |
2538 | Self: Sized, | |
2539 | { | |
532ac7d7 | 2540 | !self.eq(other) |
a7813a04 XL |
2541 | } |
2542 | ||
2543 | /// Determines if the elements of this `Iterator` are lexicographically | |
2544 | /// less than those of another. | |
2545 | #[stable(feature = "iter_order", since = "1.5.0")] | |
532ac7d7 | 2546 | fn lt<I>(self, other: I) -> bool where |
a7813a04 XL |
2547 | I: IntoIterator, |
2548 | Self::Item: PartialOrd<I::Item>, | |
2549 | Self: Sized, | |
2550 | { | |
532ac7d7 | 2551 | self.partial_cmp(other) == Some(Ordering::Less) |
a7813a04 XL |
2552 | } |
2553 | ||
2554 | /// Determines if the elements of this `Iterator` are lexicographically | |
2555 | /// less or equal to those of another. | |
2556 | #[stable(feature = "iter_order", since = "1.5.0")] | |
532ac7d7 | 2557 | fn le<I>(self, other: I) -> bool where |
a7813a04 XL |
2558 | I: IntoIterator, |
2559 | Self::Item: PartialOrd<I::Item>, | |
2560 | Self: Sized, | |
2561 | { | |
532ac7d7 XL |
2562 | match self.partial_cmp(other) { |
2563 | Some(Ordering::Less) | Some(Ordering::Equal) => true, | |
2564 | _ => false, | |
a7813a04 XL |
2565 | } |
2566 | } | |
2567 | ||
2568 | /// Determines if the elements of this `Iterator` are lexicographically | |
2569 | /// greater than those of another. | |
2570 | #[stable(feature = "iter_order", since = "1.5.0")] | |
532ac7d7 | 2571 | fn gt<I>(self, other: I) -> bool where |
a7813a04 XL |
2572 | I: IntoIterator, |
2573 | Self::Item: PartialOrd<I::Item>, | |
2574 | Self: Sized, | |
2575 | { | |
532ac7d7 | 2576 | self.partial_cmp(other) == Some(Ordering::Greater) |
a7813a04 XL |
2577 | } |
2578 | ||
2579 | /// Determines if the elements of this `Iterator` are lexicographically | |
2580 | /// greater than or equal to those of another. | |
2581 | #[stable(feature = "iter_order", since = "1.5.0")] | |
532ac7d7 | 2582 | fn ge<I>(self, other: I) -> bool where |
a7813a04 XL |
2583 | I: IntoIterator, |
2584 | Self::Item: PartialOrd<I::Item>, | |
2585 | Self: Sized, | |
2586 | { | |
532ac7d7 XL |
2587 | match self.partial_cmp(other) { |
2588 | Some(Ordering::Greater) | Some(Ordering::Equal) => true, | |
2589 | _ => false, | |
a7813a04 XL |
2590 | } |
2591 | } | |
9fa01778 XL |
2592 | |
2593 | /// Checks if the elements of this iterator are sorted. | |
2594 | /// | |
2595 | /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the | |
2596 | /// iterator yields exactly zero or one element, `true` is returned. | |
2597 | /// | |
2598 | /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition | |
2599 | /// implies that this function returns `false` if any two consecutive items are not | |
2600 | /// comparable. | |
2601 | /// | |
2602 | /// # Examples | |
2603 | /// | |
2604 | /// ``` | |
2605 | /// #![feature(is_sorted)] | |
2606 | /// | |
2607 | /// assert!([1, 2, 2, 9].iter().is_sorted()); | |
2608 | /// assert!(![1, 3, 2, 4].iter().is_sorted()); | |
2609 | /// assert!([0].iter().is_sorted()); | |
2610 | /// assert!(std::iter::empty::<i32>().is_sorted()); | |
2611 | /// assert!(![0.0, 1.0, std::f32::NAN].iter().is_sorted()); | |
2612 | /// ``` | |
2613 | #[inline] | |
2614 | #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] | |
2615 | fn is_sorted(self) -> bool | |
2616 | where | |
2617 | Self: Sized, | |
2618 | Self::Item: PartialOrd, | |
2619 | { | |
2620 | self.is_sorted_by(|a, b| a.partial_cmp(b)) | |
2621 | } | |
2622 | ||
2623 | /// Checks if the elements of this iterator are sorted using the given comparator function. | |
2624 | /// | |
2625 | /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare` | |
2626 | /// function to determine the ordering of two elements. Apart from that, it's equivalent to | |
2627 | /// [`is_sorted`]; see its documentation for more information. | |
2628 | /// | |
2629 | /// [`is_sorted`]: trait.Iterator.html#method.is_sorted | |
2630 | #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] | |
2631 | fn is_sorted_by<F>(mut self, mut compare: F) -> bool | |
2632 | where | |
2633 | Self: Sized, | |
2634 | F: FnMut(&Self::Item, &Self::Item) -> Option<Ordering> | |
2635 | { | |
2636 | let mut last = match self.next() { | |
2637 | Some(e) => e, | |
2638 | None => return true, | |
2639 | }; | |
2640 | ||
2641 | while let Some(curr) = self.next() { | |
2642 | if compare(&last, &curr) | |
2643 | .map(|o| o == Ordering::Greater) | |
2644 | .unwrap_or(true) | |
2645 | { | |
2646 | return false; | |
2647 | } | |
2648 | last = curr; | |
2649 | } | |
2650 | ||
2651 | true | |
2652 | } | |
2653 | ||
2654 | /// Checks if the elements of this iterator are sorted using the given key extraction | |
2655 | /// function. | |
2656 | /// | |
2657 | /// Instead of comparing the iterator's elements directly, this function compares the keys of | |
2658 | /// the elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see | |
2659 | /// its documentation for more information. | |
2660 | /// | |
2661 | /// [`is_sorted`]: trait.Iterator.html#method.is_sorted | |
2662 | /// | |
2663 | /// # Examples | |
2664 | /// | |
2665 | /// ``` | |
2666 | /// #![feature(is_sorted)] | |
2667 | /// | |
2668 | /// assert!(["c", "bb", "aaa"].iter().is_sorted_by_key(|s| s.len())); | |
2669 | /// assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs())); | |
2670 | /// ``` | |
2671 | #[inline] | |
2672 | #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] | |
416331ca | 2673 | fn is_sorted_by_key<F, K>(self, f: F) -> bool |
9fa01778 XL |
2674 | where |
2675 | Self: Sized, | |
416331ca | 2676 | F: FnMut(Self::Item) -> K, |
9fa01778 XL |
2677 | K: PartialOrd |
2678 | { | |
416331ca | 2679 | self.map(f).is_sorted() |
9fa01778 | 2680 | } |
a7813a04 XL |
2681 | } |
2682 | ||
532ac7d7 XL |
2683 | /// Select an element from an iterator based on the given "comparison" |
2684 | /// function. | |
a7813a04 XL |
2685 | /// |
2686 | /// This is an idiosyncratic helper to try to factor out the | |
2687 | /// commonalities of {max,min}{,_by}. In particular, this avoids | |
2688 | /// having to implement optimizations several times. | |
2689 | #[inline] | |
532ac7d7 XL |
2690 | fn select_fold1<I, F>(mut it: I, mut f: F) -> Option<I::Item> |
2691 | where | |
2692 | I: Iterator, | |
2693 | F: FnMut(&I::Item, &I::Item) -> bool, | |
a7813a04 XL |
2694 | { |
2695 | // start with the first element as our selection. This avoids | |
2696 | // having to use `Option`s inside the loop, translating to a | |
2697 | // sizeable performance gain (6x in one case). | |
abe05a73 | 2698 | it.next().map(|first| { |
532ac7d7 | 2699 | it.fold(first, |sel, x| if f(&sel, &x) { x } else { sel }) |
a7813a04 XL |
2700 | }) |
2701 | } | |
2702 | ||
2703 | #[stable(feature = "rust1", since = "1.0.0")] | |
0bf4aa26 | 2704 | impl<I: Iterator + ?Sized> Iterator for &mut I { |
a7813a04 XL |
2705 | type Item = I::Item; |
2706 | fn next(&mut self) -> Option<I::Item> { (**self).next() } | |
2707 | fn size_hint(&self) -> (usize, Option<usize>) { (**self).size_hint() } | |
476ff2be SL |
2708 | fn nth(&mut self, n: usize) -> Option<Self::Item> { |
2709 | (**self).nth(n) | |
2710 | } | |
a7813a04 | 2711 | } |