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e1599b0c XL |
1 | use crate::cmp::{self, Ordering}; |
2 | use crate::ops::{Add, 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 | /// | |
60c5eb7d XL |
204 | /// This method will call [`next`] repeatedly until [`None`] is encountered, |
205 | /// returning the number of times it saw [`Some`]. Note that [`next`] has to be | |
206 | /// called at least once even if the iterator does not have any elements. | |
a7813a04 | 207 | /// |
cc61c64b | 208 | /// [`next`]: #tymethod.next |
476ff2be | 209 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
60c5eb7d | 210 | /// [`Some`]: ../../std/option/enum.Option.html#variant.Some |
a7813a04 XL |
211 | /// |
212 | /// # Overflow Behavior | |
213 | /// | |
214 | /// The method does no guarding against overflows, so counting elements of | |
476ff2be | 215 | /// an iterator with more than [`usize::MAX`] elements either produces the |
a7813a04 XL |
216 | /// wrong result or panics. If debug assertions are enabled, a panic is |
217 | /// guaranteed. | |
218 | /// | |
219 | /// # Panics | |
220 | /// | |
476ff2be | 221 | /// This function might panic if the iterator has more than [`usize::MAX`] |
a7813a04 XL |
222 | /// elements. |
223 | /// | |
0531ce1d | 224 | /// [`usize::MAX`]: ../../std/usize/constant.MAX.html |
476ff2be | 225 | /// |
a7813a04 XL |
226 | /// # Examples |
227 | /// | |
228 | /// Basic usage: | |
229 | /// | |
230 | /// ``` | |
231 | /// let a = [1, 2, 3]; | |
232 | /// assert_eq!(a.iter().count(), 3); | |
233 | /// | |
234 | /// let a = [1, 2, 3, 4, 5]; | |
235 | /// assert_eq!(a.iter().count(), 5); | |
236 | /// ``` | |
237 | #[inline] | |
238 | #[stable(feature = "rust1", since = "1.0.0")] | |
239 | fn count(self) -> usize where Self: Sized { | |
e1599b0c XL |
240 | #[inline] |
241 | fn add1<T>(count: usize, _: T) -> usize { | |
242 | // Might overflow. | |
243 | Add::add(count, 1) | |
244 | } | |
245 | ||
246 | self.fold(0, add1) | |
a7813a04 XL |
247 | } |
248 | ||
249 | /// Consumes the iterator, returning the last element. | |
250 | /// | |
476ff2be SL |
251 | /// This method will evaluate the iterator until it returns [`None`]. While |
252 | /// doing so, it keeps track of the current element. After [`None`] is | |
a7813a04 XL |
253 | /// returned, `last()` will then return the last element it saw. |
254 | /// | |
476ff2be SL |
255 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
256 | /// | |
a7813a04 XL |
257 | /// # Examples |
258 | /// | |
259 | /// Basic usage: | |
260 | /// | |
261 | /// ``` | |
262 | /// let a = [1, 2, 3]; | |
263 | /// assert_eq!(a.iter().last(), Some(&3)); | |
264 | /// | |
265 | /// let a = [1, 2, 3, 4, 5]; | |
266 | /// assert_eq!(a.iter().last(), Some(&5)); | |
267 | /// ``` | |
268 | #[inline] | |
269 | #[stable(feature = "rust1", since = "1.0.0")] | |
270 | fn last(self) -> Option<Self::Item> where Self: Sized { | |
e1599b0c XL |
271 | #[inline] |
272 | fn some<T>(_: Option<T>, x: T) -> Option<T> { | |
273 | Some(x) | |
274 | } | |
275 | ||
276 | self.fold(None, some) | |
a7813a04 XL |
277 | } |
278 | ||
c30ab7b3 | 279 | /// Returns the `n`th element of the iterator. |
a7813a04 | 280 | /// |
a7813a04 XL |
281 | /// Like most indexing operations, the count starts from zero, so `nth(0)` |
282 | /// returns the first value, `nth(1)` the second, and so on. | |
283 | /// | |
8bb4bdeb XL |
284 | /// Note that all preceding elements, as well as the returned element, will be |
285 | /// consumed from the iterator. That means that the preceding elements will be | |
286 | /// discarded, and also that calling `nth(0)` multiple times on the same iterator | |
287 | /// will return different elements. | |
288 | /// | |
476ff2be | 289 | /// `nth()` will return [`None`] if `n` is greater than or equal to the length of the |
a7813a04 XL |
290 | /// iterator. |
291 | /// | |
476ff2be SL |
292 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
293 | /// | |
a7813a04 XL |
294 | /// # Examples |
295 | /// | |
296 | /// Basic usage: | |
297 | /// | |
298 | /// ``` | |
299 | /// let a = [1, 2, 3]; | |
300 | /// assert_eq!(a.iter().nth(1), Some(&2)); | |
301 | /// ``` | |
302 | /// | |
303 | /// Calling `nth()` multiple times doesn't rewind the iterator: | |
304 | /// | |
305 | /// ``` | |
306 | /// let a = [1, 2, 3]; | |
307 | /// | |
308 | /// let mut iter = a.iter(); | |
309 | /// | |
310 | /// assert_eq!(iter.nth(1), Some(&2)); | |
311 | /// assert_eq!(iter.nth(1), None); | |
312 | /// ``` | |
313 | /// | |
314 | /// Returning `None` if there are less than `n + 1` elements: | |
315 | /// | |
316 | /// ``` | |
317 | /// let a = [1, 2, 3]; | |
318 | /// assert_eq!(a.iter().nth(10), None); | |
319 | /// ``` | |
320 | #[inline] | |
321 | #[stable(feature = "rust1", since = "1.0.0")] | |
476ff2be | 322 | fn nth(&mut self, mut n: usize) -> Option<Self::Item> { |
a7813a04 XL |
323 | for x in self { |
324 | if n == 0 { return Some(x) } | |
325 | n -= 1; | |
326 | } | |
327 | None | |
328 | } | |
329 | ||
7cac9316 XL |
330 | /// Creates an iterator starting at the same point, but stepping by |
331 | /// the given amount at each iteration. | |
332 | /// | |
94b46f34 | 333 | /// Note 1: The first element of the iterator will always be returned, |
7cac9316 XL |
334 | /// regardless of the step given. |
335 | /// | |
94b46f34 XL |
336 | /// Note 2: The time at which ignored elements are pulled is not fixed. |
337 | /// `StepBy` behaves like the sequence `next(), nth(step-1), nth(step-1), …`, | |
338 | /// but is also free to behave like the sequence | |
339 | /// `advance_n_and_return_first(step), advance_n_and_return_first(step), …` | |
340 | /// Which way is used may change for some iterators for performance reasons. | |
341 | /// The second way will advance the iterator earlier and may consume more items. | |
342 | /// | |
343 | /// `advance_n_and_return_first` is the equivalent of: | |
344 | /// ``` | |
345 | /// fn advance_n_and_return_first<I>(iter: &mut I, total_step: usize) -> Option<I::Item> | |
346 | /// where | |
347 | /// I: Iterator, | |
348 | /// { | |
349 | /// let next = iter.next(); | |
350 | /// if total_step > 1 { | |
351 | /// iter.nth(total_step-2); | |
352 | /// } | |
353 | /// next | |
354 | /// } | |
355 | /// ``` | |
356 | /// | |
7cac9316 XL |
357 | /// # Panics |
358 | /// | |
359 | /// The method will panic if the given step is `0`. | |
360 | /// | |
361 | /// # Examples | |
362 | /// | |
363 | /// Basic usage: | |
364 | /// | |
365 | /// ``` | |
7cac9316 | 366 | /// let a = [0, 1, 2, 3, 4, 5]; |
48663c56 | 367 | /// let mut iter = a.iter().step_by(2); |
7cac9316 XL |
368 | /// |
369 | /// assert_eq!(iter.next(), Some(&0)); | |
370 | /// assert_eq!(iter.next(), Some(&2)); | |
371 | /// assert_eq!(iter.next(), Some(&4)); | |
372 | /// assert_eq!(iter.next(), None); | |
373 | /// ``` | |
374 | #[inline] | |
94b46f34 | 375 | #[stable(feature = "iterator_step_by", since = "1.28.0")] |
7cac9316 | 376 | fn step_by(self, step: usize) -> StepBy<Self> where Self: Sized { |
9fa01778 | 377 | StepBy::new(self, step) |
7cac9316 XL |
378 | } |
379 | ||
a7813a04 XL |
380 | /// Takes two iterators and creates a new iterator over both in sequence. |
381 | /// | |
382 | /// `chain()` will return a new iterator which will first iterate over | |
383 | /// values from the first iterator and then over values from the second | |
384 | /// iterator. | |
385 | /// | |
386 | /// In other words, it links two iterators together, in a chain. 🔗 | |
387 | /// | |
e74abb32 XL |
388 | /// [`once`] is commonly used to adapt a single value into a chain of |
389 | /// other kinds of iteration. | |
390 | /// | |
a7813a04 XL |
391 | /// # Examples |
392 | /// | |
393 | /// Basic usage: | |
394 | /// | |
395 | /// ``` | |
396 | /// let a1 = [1, 2, 3]; | |
397 | /// let a2 = [4, 5, 6]; | |
398 | /// | |
399 | /// let mut iter = a1.iter().chain(a2.iter()); | |
400 | /// | |
401 | /// assert_eq!(iter.next(), Some(&1)); | |
402 | /// assert_eq!(iter.next(), Some(&2)); | |
403 | /// assert_eq!(iter.next(), Some(&3)); | |
404 | /// assert_eq!(iter.next(), Some(&4)); | |
405 | /// assert_eq!(iter.next(), Some(&5)); | |
406 | /// assert_eq!(iter.next(), Some(&6)); | |
407 | /// assert_eq!(iter.next(), None); | |
408 | /// ``` | |
409 | /// | |
410 | /// Since the argument to `chain()` uses [`IntoIterator`], we can pass | |
411 | /// anything that can be converted into an [`Iterator`], not just an | |
412 | /// [`Iterator`] itself. For example, slices (`&[T]`) implement | |
413 | /// [`IntoIterator`], and so can be passed to `chain()` directly: | |
414 | /// | |
a7813a04 XL |
415 | /// ``` |
416 | /// let s1 = &[1, 2, 3]; | |
417 | /// let s2 = &[4, 5, 6]; | |
418 | /// | |
419 | /// let mut iter = s1.iter().chain(s2); | |
420 | /// | |
421 | /// assert_eq!(iter.next(), Some(&1)); | |
422 | /// assert_eq!(iter.next(), Some(&2)); | |
423 | /// assert_eq!(iter.next(), Some(&3)); | |
424 | /// assert_eq!(iter.next(), Some(&4)); | |
425 | /// assert_eq!(iter.next(), Some(&5)); | |
426 | /// assert_eq!(iter.next(), Some(&6)); | |
427 | /// assert_eq!(iter.next(), None); | |
428 | /// ``` | |
e74abb32 XL |
429 | /// |
430 | /// If you work with Windows API, you may wish to convert [`OsStr`] to `Vec<u16>`: | |
431 | /// | |
432 | /// ``` | |
433 | /// #[cfg(windows)] | |
434 | /// fn os_str_to_utf16(s: &std::ffi::OsStr) -> Vec<u16> { | |
435 | /// use std::os::windows::ffi::OsStrExt; | |
436 | /// s.encode_wide().chain(std::iter::once(0)).collect() | |
437 | /// } | |
438 | /// ``` | |
439 | /// | |
440 | /// [`once`]: fn.once.html | |
441 | /// [`Iterator`]: trait.Iterator.html | |
442 | /// [`IntoIterator`]: trait.IntoIterator.html | |
443 | /// [`OsStr`]: ../../std/ffi/struct.OsStr.html | |
a7813a04 XL |
444 | #[inline] |
445 | #[stable(feature = "rust1", since = "1.0.0")] | |
446 | fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> where | |
447 | Self: Sized, U: IntoIterator<Item=Self::Item>, | |
448 | { | |
9fa01778 | 449 | Chain::new(self, other.into_iter()) |
a7813a04 XL |
450 | } |
451 | ||
452 | /// 'Zips up' two iterators into a single iterator of pairs. | |
453 | /// | |
454 | /// `zip()` returns a new iterator that will iterate over two other | |
455 | /// iterators, returning a tuple where the first element comes from the | |
456 | /// first iterator, and the second element comes from the second iterator. | |
457 | /// | |
458 | /// In other words, it zips two iterators together, into a single one. | |
459 | /// | |
8faf50e0 XL |
460 | /// If either iterator returns [`None`], [`next`] from the zipped iterator |
461 | /// will return [`None`]. If the first iterator returns [`None`], `zip` will | |
462 | /// short-circuit and `next` will not be called on the second iterator. | |
a7813a04 XL |
463 | /// |
464 | /// # Examples | |
465 | /// | |
466 | /// Basic usage: | |
467 | /// | |
468 | /// ``` | |
469 | /// let a1 = [1, 2, 3]; | |
470 | /// let a2 = [4, 5, 6]; | |
471 | /// | |
472 | /// let mut iter = a1.iter().zip(a2.iter()); | |
473 | /// | |
474 | /// assert_eq!(iter.next(), Some((&1, &4))); | |
475 | /// assert_eq!(iter.next(), Some((&2, &5))); | |
476 | /// assert_eq!(iter.next(), Some((&3, &6))); | |
477 | /// assert_eq!(iter.next(), None); | |
478 | /// ``` | |
479 | /// | |
480 | /// Since the argument to `zip()` uses [`IntoIterator`], we can pass | |
481 | /// anything that can be converted into an [`Iterator`], not just an | |
482 | /// [`Iterator`] itself. For example, slices (`&[T]`) implement | |
483 | /// [`IntoIterator`], and so can be passed to `zip()` directly: | |
484 | /// | |
485 | /// [`IntoIterator`]: trait.IntoIterator.html | |
486 | /// [`Iterator`]: trait.Iterator.html | |
487 | /// | |
488 | /// ``` | |
489 | /// let s1 = &[1, 2, 3]; | |
490 | /// let s2 = &[4, 5, 6]; | |
491 | /// | |
492 | /// let mut iter = s1.iter().zip(s2); | |
493 | /// | |
494 | /// assert_eq!(iter.next(), Some((&1, &4))); | |
495 | /// assert_eq!(iter.next(), Some((&2, &5))); | |
496 | /// assert_eq!(iter.next(), Some((&3, &6))); | |
497 | /// assert_eq!(iter.next(), None); | |
498 | /// ``` | |
499 | /// | |
500 | /// `zip()` is often used to zip an infinite iterator to a finite one. | |
476ff2be | 501 | /// This works because the finite iterator will eventually return [`None`], |
cc61c64b | 502 | /// ending the zipper. Zipping with `(0..)` can look a lot like [`enumerate`]: |
a7813a04 XL |
503 | /// |
504 | /// ``` | |
505 | /// let enumerate: Vec<_> = "foo".chars().enumerate().collect(); | |
506 | /// | |
507 | /// let zipper: Vec<_> = (0..).zip("foo".chars()).collect(); | |
508 | /// | |
509 | /// assert_eq!((0, 'f'), enumerate[0]); | |
510 | /// assert_eq!((0, 'f'), zipper[0]); | |
511 | /// | |
512 | /// assert_eq!((1, 'o'), enumerate[1]); | |
513 | /// assert_eq!((1, 'o'), zipper[1]); | |
514 | /// | |
515 | /// assert_eq!((2, 'o'), enumerate[2]); | |
516 | /// assert_eq!((2, 'o'), zipper[2]); | |
517 | /// ``` | |
518 | /// | |
cc61c64b XL |
519 | /// [`enumerate`]: trait.Iterator.html#method.enumerate |
520 | /// [`next`]: ../../std/iter/trait.Iterator.html#tymethod.next | |
476ff2be | 521 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
a7813a04 XL |
522 | #[inline] |
523 | #[stable(feature = "rust1", since = "1.0.0")] | |
524 | fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> where | |
525 | Self: Sized, U: IntoIterator | |
526 | { | |
3157f602 | 527 | Zip::new(self, other.into_iter()) |
a7813a04 XL |
528 | } |
529 | ||
530 | /// Takes a closure and creates an iterator which calls that closure on each | |
531 | /// element. | |
532 | /// | |
533 | /// `map()` transforms one iterator into another, by means of its argument: | |
a1dfa0c6 | 534 | /// something that implements [`FnMut`]. It produces a new iterator which |
a7813a04 XL |
535 | /// calls this closure on each element of the original iterator. |
536 | /// | |
537 | /// If you are good at thinking in types, you can think of `map()` like this: | |
538 | /// If you have an iterator that gives you elements of some type `A`, and | |
539 | /// you want an iterator of some other type `B`, you can use `map()`, | |
540 | /// passing a closure that takes an `A` and returns a `B`. | |
541 | /// | |
542 | /// `map()` is conceptually similar to a [`for`] loop. However, as `map()` is | |
543 | /// lazy, it is best used when you're already working with other iterators. | |
544 | /// If you're doing some sort of looping for a side effect, it's considered | |
545 | /// more idiomatic to use [`for`] than `map()`. | |
546 | /// | |
13cf67c4 | 547 | /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for |
a1dfa0c6 | 548 | /// [`FnMut`]: ../../std/ops/trait.FnMut.html |
a7813a04 XL |
549 | /// |
550 | /// # Examples | |
551 | /// | |
552 | /// Basic usage: | |
553 | /// | |
554 | /// ``` | |
555 | /// let a = [1, 2, 3]; | |
556 | /// | |
48663c56 | 557 | /// let mut iter = a.iter().map(|x| 2 * x); |
a7813a04 XL |
558 | /// |
559 | /// assert_eq!(iter.next(), Some(2)); | |
560 | /// assert_eq!(iter.next(), Some(4)); | |
561 | /// assert_eq!(iter.next(), Some(6)); | |
562 | /// assert_eq!(iter.next(), None); | |
563 | /// ``` | |
564 | /// | |
565 | /// If you're doing some sort of side effect, prefer [`for`] to `map()`: | |
566 | /// | |
567 | /// ``` | |
568 | /// # #![allow(unused_must_use)] | |
569 | /// // don't do this: | |
570 | /// (0..5).map(|x| println!("{}", x)); | |
571 | /// | |
572 | /// // it won't even execute, as it is lazy. Rust will warn you about this. | |
573 | /// | |
574 | /// // Instead, use for: | |
575 | /// for x in 0..5 { | |
576 | /// println!("{}", x); | |
577 | /// } | |
578 | /// ``` | |
579 | #[inline] | |
580 | #[stable(feature = "rust1", since = "1.0.0")] | |
581 | fn map<B, F>(self, f: F) -> Map<Self, F> where | |
582 | Self: Sized, F: FnMut(Self::Item) -> B, | |
583 | { | |
9fa01778 | 584 | Map::new(self, f) |
a7813a04 XL |
585 | } |
586 | ||
041b39d2 XL |
587 | /// Calls a closure on each element of an iterator. |
588 | /// | |
589 | /// This is equivalent to using a [`for`] loop on the iterator, although | |
9fa01778 | 590 | /// `break` and `continue` are not possible from a closure. It's generally |
041b39d2 | 591 | /// more idiomatic to use a `for` loop, but `for_each` may be more legible |
9fa01778 | 592 | /// when processing items at the end of longer iterator chains. In some |
041b39d2 XL |
593 | /// cases `for_each` may also be faster than a loop, because it will use |
594 | /// internal iteration on adaptors like `Chain`. | |
595 | /// | |
13cf67c4 | 596 | /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for |
041b39d2 XL |
597 | /// |
598 | /// # Examples | |
599 | /// | |
600 | /// Basic usage: | |
601 | /// | |
602 | /// ``` | |
041b39d2 XL |
603 | /// use std::sync::mpsc::channel; |
604 | /// | |
605 | /// let (tx, rx) = channel(); | |
606 | /// (0..5).map(|x| x * 2 + 1) | |
607 | /// .for_each(move |x| tx.send(x).unwrap()); | |
608 | /// | |
609 | /// let v: Vec<_> = rx.iter().collect(); | |
610 | /// assert_eq!(v, vec![1, 3, 5, 7, 9]); | |
611 | /// ``` | |
612 | /// | |
613 | /// For such a small example, a `for` loop may be cleaner, but `for_each` | |
614 | /// might be preferable to keep a functional style with longer iterators: | |
615 | /// | |
616 | /// ``` | |
041b39d2 XL |
617 | /// (0..5).flat_map(|x| x * 100 .. x * 110) |
618 | /// .enumerate() | |
619 | /// .filter(|&(i, x)| (i + x) % 3 == 0) | |
620 | /// .for_each(|(i, x)| println!("{}:{}", i, x)); | |
621 | /// ``` | |
622 | #[inline] | |
3b2f2976 | 623 | #[stable(feature = "iterator_for_each", since = "1.21.0")] |
e1599b0c | 624 | fn for_each<F>(self, f: F) where |
041b39d2 XL |
625 | Self: Sized, F: FnMut(Self::Item), |
626 | { | |
e1599b0c XL |
627 | #[inline] |
628 | fn call<T>(mut f: impl FnMut(T)) -> impl FnMut((), T) { | |
629 | move |(), item| f(item) | |
630 | } | |
631 | ||
632 | self.fold((), call(f)); | |
041b39d2 XL |
633 | } |
634 | ||
a7813a04 XL |
635 | /// Creates an iterator which uses a closure to determine if an element |
636 | /// should be yielded. | |
637 | /// | |
638 | /// The closure must return `true` or `false`. `filter()` creates an | |
639 | /// iterator which calls this closure on each element. If the closure | |
640 | /// returns `true`, then the element is returned. If the closure returns | |
641 | /// `false`, it will try again, and call the closure on the next element, | |
642 | /// seeing if it passes the test. | |
643 | /// | |
644 | /// # Examples | |
645 | /// | |
646 | /// Basic usage: | |
647 | /// | |
648 | /// ``` | |
649 | /// let a = [0i32, 1, 2]; | |
650 | /// | |
48663c56 | 651 | /// let mut iter = a.iter().filter(|x| x.is_positive()); |
a7813a04 XL |
652 | /// |
653 | /// assert_eq!(iter.next(), Some(&1)); | |
654 | /// assert_eq!(iter.next(), Some(&2)); | |
655 | /// assert_eq!(iter.next(), None); | |
656 | /// ``` | |
657 | /// | |
658 | /// Because the closure passed to `filter()` takes a reference, and many | |
659 | /// iterators iterate over references, this leads to a possibly confusing | |
660 | /// situation, where the type of the closure is a double reference: | |
661 | /// | |
662 | /// ``` | |
663 | /// let a = [0, 1, 2]; | |
664 | /// | |
48663c56 | 665 | /// let mut iter = a.iter().filter(|x| **x > 1); // need two *s! |
a7813a04 XL |
666 | /// |
667 | /// assert_eq!(iter.next(), Some(&2)); | |
668 | /// assert_eq!(iter.next(), None); | |
669 | /// ``` | |
670 | /// | |
671 | /// It's common to instead use destructuring on the argument to strip away | |
672 | /// one: | |
673 | /// | |
674 | /// ``` | |
675 | /// let a = [0, 1, 2]; | |
676 | /// | |
48663c56 | 677 | /// let mut iter = a.iter().filter(|&x| *x > 1); // both & and * |
a7813a04 XL |
678 | /// |
679 | /// assert_eq!(iter.next(), Some(&2)); | |
680 | /// assert_eq!(iter.next(), None); | |
681 | /// ``` | |
682 | /// | |
683 | /// or both: | |
684 | /// | |
685 | /// ``` | |
686 | /// let a = [0, 1, 2]; | |
687 | /// | |
48663c56 | 688 | /// let mut iter = a.iter().filter(|&&x| x > 1); // two &s |
a7813a04 XL |
689 | /// |
690 | /// assert_eq!(iter.next(), Some(&2)); | |
691 | /// assert_eq!(iter.next(), None); | |
692 | /// ``` | |
693 | /// | |
694 | /// of these layers. | |
695 | #[inline] | |
696 | #[stable(feature = "rust1", since = "1.0.0")] | |
697 | fn filter<P>(self, predicate: P) -> Filter<Self, P> where | |
698 | Self: Sized, P: FnMut(&Self::Item) -> bool, | |
699 | { | |
9fa01778 | 700 | Filter::new(self, predicate) |
a7813a04 XL |
701 | } |
702 | ||
703 | /// Creates an iterator that both filters and maps. | |
704 | /// | |
cc61c64b | 705 | /// The closure must return an [`Option<T>`]. `filter_map` creates an |
a7813a04 | 706 | /// iterator which calls this closure on each element. If the closure |
476ff2be SL |
707 | /// returns [`Some(element)`][`Some`], then that element is returned. If the |
708 | /// closure returns [`None`], it will try again, and call the closure on the | |
709 | /// next element, seeing if it will return [`Some`]. | |
a7813a04 | 710 | /// |
3b2f2976 | 711 | /// Why `filter_map` and not just [`filter`] and [`map`]? The key is in this |
a7813a04 XL |
712 | /// part: |
713 | /// | |
cc61c64b XL |
714 | /// [`filter`]: #method.filter |
715 | /// [`map`]: #method.map | |
a7813a04 | 716 | /// |
476ff2be | 717 | /// > If the closure returns [`Some(element)`][`Some`], then that element is returned. |
a7813a04 XL |
718 | /// |
719 | /// In other words, it removes the [`Option<T>`] layer automatically. If your | |
720 | /// mapping is already returning an [`Option<T>`] and you want to skip over | |
cc61c64b | 721 | /// [`None`]s, then `filter_map` is much, much nicer to use. |
a7813a04 XL |
722 | /// |
723 | /// # Examples | |
724 | /// | |
725 | /// Basic usage: | |
726 | /// | |
727 | /// ``` | |
ff7c6d11 | 728 | /// let a = ["1", "lol", "3", "NaN", "5"]; |
a7813a04 XL |
729 | /// |
730 | /// let mut iter = a.iter().filter_map(|s| s.parse().ok()); | |
731 | /// | |
732 | /// assert_eq!(iter.next(), Some(1)); | |
ff7c6d11 XL |
733 | /// assert_eq!(iter.next(), Some(3)); |
734 | /// assert_eq!(iter.next(), Some(5)); | |
a7813a04 XL |
735 | /// assert_eq!(iter.next(), None); |
736 | /// ``` | |
737 | /// | |
cc61c64b | 738 | /// Here's the same example, but with [`filter`] and [`map`]: |
a7813a04 XL |
739 | /// |
740 | /// ``` | |
ff7c6d11 XL |
741 | /// let a = ["1", "lol", "3", "NaN", "5"]; |
742 | /// let mut iter = a.iter().map(|s| s.parse()).filter(|s| s.is_ok()).map(|s| s.unwrap()); | |
3b2f2976 | 743 | /// assert_eq!(iter.next(), Some(1)); |
ff7c6d11 XL |
744 | /// assert_eq!(iter.next(), Some(3)); |
745 | /// assert_eq!(iter.next(), Some(5)); | |
a7813a04 XL |
746 | /// assert_eq!(iter.next(), None); |
747 | /// ``` | |
748 | /// | |
476ff2be SL |
749 | /// [`Option<T>`]: ../../std/option/enum.Option.html |
750 | /// [`Some`]: ../../std/option/enum.Option.html#variant.Some | |
751 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
a7813a04 XL |
752 | #[inline] |
753 | #[stable(feature = "rust1", since = "1.0.0")] | |
754 | fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where | |
755 | Self: Sized, F: FnMut(Self::Item) -> Option<B>, | |
756 | { | |
9fa01778 | 757 | FilterMap::new(self, f) |
a7813a04 XL |
758 | } |
759 | ||
760 | /// Creates an iterator which gives the current iteration count as well as | |
761 | /// the next value. | |
762 | /// | |
763 | /// The iterator returned yields pairs `(i, val)`, where `i` is the | |
764 | /// current index of iteration and `val` is the value returned by the | |
765 | /// iterator. | |
766 | /// | |
767 | /// `enumerate()` keeps its count as a [`usize`]. If you want to count by a | |
cc61c64b | 768 | /// different sized integer, the [`zip`] function provides similar |
a7813a04 XL |
769 | /// functionality. |
770 | /// | |
a7813a04 XL |
771 | /// # Overflow Behavior |
772 | /// | |
773 | /// The method does no guarding against overflows, so enumerating more than | |
774 | /// [`usize::MAX`] elements either produces the wrong result or panics. If | |
775 | /// debug assertions are enabled, a panic is guaranteed. | |
776 | /// | |
a7813a04 XL |
777 | /// # Panics |
778 | /// | |
779 | /// The returned iterator might panic if the to-be-returned index would | |
476ff2be SL |
780 | /// overflow a [`usize`]. |
781 | /// | |
782 | /// [`usize::MAX`]: ../../std/usize/constant.MAX.html | |
783 | /// [`usize`]: ../../std/primitive.usize.html | |
cc61c64b | 784 | /// [`zip`]: #method.zip |
a7813a04 XL |
785 | /// |
786 | /// # Examples | |
787 | /// | |
788 | /// ``` | |
789 | /// let a = ['a', 'b', 'c']; | |
790 | /// | |
791 | /// let mut iter = a.iter().enumerate(); | |
792 | /// | |
793 | /// assert_eq!(iter.next(), Some((0, &'a'))); | |
794 | /// assert_eq!(iter.next(), Some((1, &'b'))); | |
795 | /// assert_eq!(iter.next(), Some((2, &'c'))); | |
796 | /// assert_eq!(iter.next(), None); | |
797 | /// ``` | |
798 | #[inline] | |
799 | #[stable(feature = "rust1", since = "1.0.0")] | |
800 | fn enumerate(self) -> Enumerate<Self> where Self: Sized { | |
9fa01778 | 801 | Enumerate::new(self) |
a7813a04 XL |
802 | } |
803 | ||
804 | /// Creates an iterator which can use `peek` to look at the next element of | |
805 | /// the iterator without consuming it. | |
806 | /// | |
cc61c64b | 807 | /// Adds a [`peek`] method to an iterator. See its documentation for |
a7813a04 XL |
808 | /// more information. |
809 | /// | |
cc61c64b | 810 | /// Note that the underlying iterator is still advanced when [`peek`] is |
a7813a04 | 811 | /// called for the first time: In order to retrieve the next element, |
7cac9316 XL |
812 | /// [`next`] is called on the underlying iterator, hence any side effects (i.e. |
813 | /// anything other than fetching the next value) of the [`next`] method | |
814 | /// will occur. | |
a7813a04 | 815 | /// |
cc61c64b XL |
816 | /// [`peek`]: struct.Peekable.html#method.peek |
817 | /// [`next`]: ../../std/iter/trait.Iterator.html#tymethod.next | |
a7813a04 XL |
818 | /// |
819 | /// # Examples | |
820 | /// | |
821 | /// Basic usage: | |
822 | /// | |
823 | /// ``` | |
824 | /// let xs = [1, 2, 3]; | |
825 | /// | |
826 | /// let mut iter = xs.iter().peekable(); | |
827 | /// | |
828 | /// // peek() lets us see into the future | |
829 | /// assert_eq!(iter.peek(), Some(&&1)); | |
830 | /// assert_eq!(iter.next(), Some(&1)); | |
831 | /// | |
832 | /// assert_eq!(iter.next(), Some(&2)); | |
833 | /// | |
834 | /// // we can peek() multiple times, the iterator won't advance | |
835 | /// assert_eq!(iter.peek(), Some(&&3)); | |
836 | /// assert_eq!(iter.peek(), Some(&&3)); | |
837 | /// | |
838 | /// assert_eq!(iter.next(), Some(&3)); | |
839 | /// | |
840 | /// // after the iterator is finished, so is peek() | |
841 | /// assert_eq!(iter.peek(), None); | |
842 | /// assert_eq!(iter.next(), None); | |
843 | /// ``` | |
844 | #[inline] | |
845 | #[stable(feature = "rust1", since = "1.0.0")] | |
846 | fn peekable(self) -> Peekable<Self> where Self: Sized { | |
9fa01778 | 847 | Peekable::new(self) |
a7813a04 XL |
848 | } |
849 | ||
cc61c64b | 850 | /// Creates an iterator that [`skip`]s elements based on a predicate. |
a7813a04 | 851 | /// |
cc61c64b | 852 | /// [`skip`]: #method.skip |
a7813a04 XL |
853 | /// |
854 | /// `skip_while()` takes a closure as an argument. It will call this | |
855 | /// closure on each element of the iterator, and ignore elements | |
856 | /// until it returns `false`. | |
857 | /// | |
858 | /// After `false` is returned, `skip_while()`'s job is over, and the | |
859 | /// rest of the elements are yielded. | |
860 | /// | |
861 | /// # Examples | |
862 | /// | |
863 | /// Basic usage: | |
864 | /// | |
865 | /// ``` | |
866 | /// let a = [-1i32, 0, 1]; | |
867 | /// | |
48663c56 | 868 | /// let mut iter = a.iter().skip_while(|x| x.is_negative()); |
a7813a04 XL |
869 | /// |
870 | /// assert_eq!(iter.next(), Some(&0)); | |
871 | /// assert_eq!(iter.next(), Some(&1)); | |
872 | /// assert_eq!(iter.next(), None); | |
873 | /// ``` | |
874 | /// | |
875 | /// Because the closure passed to `skip_while()` takes a reference, and many | |
876 | /// iterators iterate over references, this leads to a possibly confusing | |
877 | /// situation, where the type of the closure is a double reference: | |
878 | /// | |
879 | /// ``` | |
880 | /// let a = [-1, 0, 1]; | |
881 | /// | |
48663c56 | 882 | /// let mut iter = a.iter().skip_while(|x| **x < 0); // need two *s! |
a7813a04 XL |
883 | /// |
884 | /// assert_eq!(iter.next(), Some(&0)); | |
885 | /// assert_eq!(iter.next(), Some(&1)); | |
886 | /// assert_eq!(iter.next(), None); | |
887 | /// ``` | |
888 | /// | |
889 | /// Stopping after an initial `false`: | |
890 | /// | |
891 | /// ``` | |
892 | /// let a = [-1, 0, 1, -2]; | |
893 | /// | |
48663c56 | 894 | /// let mut iter = a.iter().skip_while(|x| **x < 0); |
a7813a04 XL |
895 | /// |
896 | /// assert_eq!(iter.next(), Some(&0)); | |
897 | /// assert_eq!(iter.next(), Some(&1)); | |
898 | /// | |
899 | /// // while this would have been false, since we already got a false, | |
900 | /// // skip_while() isn't used any more | |
901 | /// assert_eq!(iter.next(), Some(&-2)); | |
902 | /// | |
903 | /// assert_eq!(iter.next(), None); | |
904 | /// ``` | |
905 | #[inline] | |
906 | #[stable(feature = "rust1", since = "1.0.0")] | |
907 | fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where | |
908 | Self: Sized, P: FnMut(&Self::Item) -> bool, | |
909 | { | |
9fa01778 | 910 | SkipWhile::new(self, predicate) |
a7813a04 XL |
911 | } |
912 | ||
913 | /// Creates an iterator that yields elements based on a predicate. | |
914 | /// | |
915 | /// `take_while()` takes a closure as an argument. It will call this | |
916 | /// closure on each element of the iterator, and yield elements | |
917 | /// while it returns `true`. | |
918 | /// | |
919 | /// After `false` is returned, `take_while()`'s job is over, and the | |
920 | /// rest of the elements are ignored. | |
921 | /// | |
922 | /// # Examples | |
923 | /// | |
924 | /// Basic usage: | |
925 | /// | |
926 | /// ``` | |
927 | /// let a = [-1i32, 0, 1]; | |
928 | /// | |
48663c56 | 929 | /// let mut iter = a.iter().take_while(|x| x.is_negative()); |
a7813a04 XL |
930 | /// |
931 | /// assert_eq!(iter.next(), Some(&-1)); | |
932 | /// assert_eq!(iter.next(), None); | |
933 | /// ``` | |
934 | /// | |
935 | /// Because the closure passed to `take_while()` takes a reference, and many | |
936 | /// iterators iterate over references, this leads to a possibly confusing | |
937 | /// situation, where the type of the closure is a double reference: | |
938 | /// | |
939 | /// ``` | |
940 | /// let a = [-1, 0, 1]; | |
941 | /// | |
48663c56 | 942 | /// let mut iter = a.iter().take_while(|x| **x < 0); // need two *s! |
a7813a04 XL |
943 | /// |
944 | /// assert_eq!(iter.next(), Some(&-1)); | |
945 | /// assert_eq!(iter.next(), None); | |
946 | /// ``` | |
947 | /// | |
948 | /// Stopping after an initial `false`: | |
949 | /// | |
950 | /// ``` | |
951 | /// let a = [-1, 0, 1, -2]; | |
952 | /// | |
48663c56 | 953 | /// let mut iter = a.iter().take_while(|x| **x < 0); |
a7813a04 XL |
954 | /// |
955 | /// assert_eq!(iter.next(), Some(&-1)); | |
956 | /// | |
957 | /// // We have more elements that are less than zero, but since we already | |
958 | /// // got a false, take_while() isn't used any more | |
959 | /// assert_eq!(iter.next(), None); | |
960 | /// ``` | |
961 | /// | |
962 | /// Because `take_while()` needs to look at the value in order to see if it | |
963 | /// should be included or not, consuming iterators will see that it is | |
964 | /// removed: | |
965 | /// | |
966 | /// ``` | |
967 | /// let a = [1, 2, 3, 4]; | |
48663c56 | 968 | /// let mut iter = a.iter(); |
a7813a04 XL |
969 | /// |
970 | /// let result: Vec<i32> = iter.by_ref() | |
971 | /// .take_while(|n| **n != 3) | |
972 | /// .cloned() | |
973 | /// .collect(); | |
974 | /// | |
975 | /// assert_eq!(result, &[1, 2]); | |
976 | /// | |
977 | /// let result: Vec<i32> = iter.cloned().collect(); | |
978 | /// | |
979 | /// assert_eq!(result, &[4]); | |
980 | /// ``` | |
981 | /// | |
982 | /// The `3` is no longer there, because it was consumed in order to see if | |
9fa01778 | 983 | /// the iteration should stop, but wasn't placed back into the iterator. |
a7813a04 XL |
984 | #[inline] |
985 | #[stable(feature = "rust1", since = "1.0.0")] | |
986 | fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where | |
987 | Self: Sized, P: FnMut(&Self::Item) -> bool, | |
988 | { | |
9fa01778 | 989 | TakeWhile::new(self, predicate) |
a7813a04 XL |
990 | } |
991 | ||
992 | /// Creates an iterator that skips the first `n` elements. | |
993 | /// | |
994 | /// After they have been consumed, the rest of the elements are yielded. | |
dc9dc135 | 995 | /// Rather than overriding this method directly, instead override the `nth` method. |
a7813a04 XL |
996 | /// |
997 | /// # Examples | |
998 | /// | |
999 | /// Basic usage: | |
1000 | /// | |
1001 | /// ``` | |
1002 | /// let a = [1, 2, 3]; | |
1003 | /// | |
1004 | /// let mut iter = a.iter().skip(2); | |
1005 | /// | |
1006 | /// assert_eq!(iter.next(), Some(&3)); | |
1007 | /// assert_eq!(iter.next(), None); | |
1008 | /// ``` | |
1009 | #[inline] | |
1010 | #[stable(feature = "rust1", since = "1.0.0")] | |
1011 | fn skip(self, n: usize) -> Skip<Self> where Self: Sized { | |
9fa01778 | 1012 | Skip::new(self, n) |
a7813a04 XL |
1013 | } |
1014 | ||
1015 | /// Creates an iterator that yields its first `n` elements. | |
1016 | /// | |
1017 | /// # Examples | |
1018 | /// | |
1019 | /// Basic usage: | |
1020 | /// | |
1021 | /// ``` | |
1022 | /// let a = [1, 2, 3]; | |
1023 | /// | |
1024 | /// let mut iter = a.iter().take(2); | |
1025 | /// | |
1026 | /// assert_eq!(iter.next(), Some(&1)); | |
1027 | /// assert_eq!(iter.next(), Some(&2)); | |
1028 | /// assert_eq!(iter.next(), None); | |
1029 | /// ``` | |
1030 | /// | |
1031 | /// `take()` is often used with an infinite iterator, to make it finite: | |
1032 | /// | |
1033 | /// ``` | |
1034 | /// let mut iter = (0..).take(3); | |
1035 | /// | |
1036 | /// assert_eq!(iter.next(), Some(0)); | |
1037 | /// assert_eq!(iter.next(), Some(1)); | |
1038 | /// assert_eq!(iter.next(), Some(2)); | |
1039 | /// assert_eq!(iter.next(), None); | |
1040 | /// ``` | |
1041 | #[inline] | |
1042 | #[stable(feature = "rust1", since = "1.0.0")] | |
1043 | fn take(self, n: usize) -> Take<Self> where Self: Sized, { | |
9fa01778 | 1044 | Take::new(self, n) |
a7813a04 XL |
1045 | } |
1046 | ||
cc61c64b | 1047 | /// An iterator adaptor similar to [`fold`] that holds internal state and |
a7813a04 XL |
1048 | /// produces a new iterator. |
1049 | /// | |
cc61c64b | 1050 | /// [`fold`]: #method.fold |
a7813a04 XL |
1051 | /// |
1052 | /// `scan()` takes two arguments: an initial value which seeds the internal | |
1053 | /// state, and a closure with two arguments, the first being a mutable | |
1054 | /// reference to the internal state and the second an iterator element. | |
1055 | /// The closure can assign to the internal state to share state between | |
1056 | /// iterations. | |
1057 | /// | |
1058 | /// On iteration, the closure will be applied to each element of the | |
1059 | /// iterator and the return value from the closure, an [`Option`], is | |
1060 | /// yielded by the iterator. | |
1061 | /// | |
1062 | /// [`Option`]: ../../std/option/enum.Option.html | |
1063 | /// | |
1064 | /// # Examples | |
1065 | /// | |
1066 | /// Basic usage: | |
1067 | /// | |
1068 | /// ``` | |
1069 | /// let a = [1, 2, 3]; | |
1070 | /// | |
1071 | /// let mut iter = a.iter().scan(1, |state, &x| { | |
1072 | /// // each iteration, we'll multiply the state by the element | |
1073 | /// *state = *state * x; | |
1074 | /// | |
0531ce1d XL |
1075 | /// // then, we'll yield the negation of the state |
1076 | /// Some(-*state) | |
a7813a04 XL |
1077 | /// }); |
1078 | /// | |
0531ce1d XL |
1079 | /// assert_eq!(iter.next(), Some(-1)); |
1080 | /// assert_eq!(iter.next(), Some(-2)); | |
1081 | /// assert_eq!(iter.next(), Some(-6)); | |
a7813a04 XL |
1082 | /// assert_eq!(iter.next(), None); |
1083 | /// ``` | |
1084 | #[inline] | |
1085 | #[stable(feature = "rust1", since = "1.0.0")] | |
1086 | fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> | |
1087 | where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option<B>, | |
1088 | { | |
9fa01778 | 1089 | Scan::new(self, initial_state, f) |
a7813a04 XL |
1090 | } |
1091 | ||
1092 | /// Creates an iterator that works like map, but flattens nested structure. | |
1093 | /// | |
cc61c64b | 1094 | /// The [`map`] adapter is very useful, but only when the closure |
a7813a04 XL |
1095 | /// argument produces values. If it produces an iterator instead, there's |
1096 | /// an extra layer of indirection. `flat_map()` will remove this extra layer | |
1097 | /// on its own. | |
1098 | /// | |
83c7162d | 1099 | /// You can think of `flat_map(f)` as the semantic equivalent |
0531ce1d XL |
1100 | /// of [`map`]ping, and then [`flatten`]ing as in `map(f).flatten()`. |
1101 | /// | |
cc61c64b | 1102 | /// Another way of thinking about `flat_map()`: [`map`]'s closure returns |
a7813a04 XL |
1103 | /// one item for each element, and `flat_map()`'s closure returns an |
1104 | /// iterator for each element. | |
1105 | /// | |
cc61c64b | 1106 | /// [`map`]: #method.map |
0531ce1d | 1107 | /// [`flatten`]: #method.flatten |
476ff2be | 1108 | /// |
a7813a04 XL |
1109 | /// # Examples |
1110 | /// | |
1111 | /// Basic usage: | |
1112 | /// | |
1113 | /// ``` | |
1114 | /// let words = ["alpha", "beta", "gamma"]; | |
1115 | /// | |
1116 | /// // chars() returns an iterator | |
1117 | /// let merged: String = words.iter() | |
1118 | /// .flat_map(|s| s.chars()) | |
1119 | /// .collect(); | |
1120 | /// assert_eq!(merged, "alphabetagamma"); | |
1121 | /// ``` | |
1122 | #[inline] | |
1123 | #[stable(feature = "rust1", since = "1.0.0")] | |
1124 | fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> | |
1125 | where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U, | |
1126 | { | |
9fa01778 | 1127 | FlatMap::new(self, f) |
0531ce1d XL |
1128 | } |
1129 | ||
1130 | /// Creates an iterator that flattens nested structure. | |
1131 | /// | |
1132 | /// This is useful when you have an iterator of iterators or an iterator of | |
1133 | /// things that can be turned into iterators and you want to remove one | |
1134 | /// level of indirection. | |
1135 | /// | |
1136 | /// # Examples | |
1137 | /// | |
1138 | /// Basic usage: | |
1139 | /// | |
1140 | /// ``` | |
0531ce1d XL |
1141 | /// let data = vec![vec![1, 2, 3, 4], vec![5, 6]]; |
1142 | /// let flattened = data.into_iter().flatten().collect::<Vec<u8>>(); | |
1143 | /// assert_eq!(flattened, &[1, 2, 3, 4, 5, 6]); | |
1144 | /// ``` | |
1145 | /// | |
1146 | /// Mapping and then flattening: | |
1147 | /// | |
1148 | /// ``` | |
0531ce1d XL |
1149 | /// let words = ["alpha", "beta", "gamma"]; |
1150 | /// | |
1151 | /// // chars() returns an iterator | |
1152 | /// let merged: String = words.iter() | |
1153 | /// .map(|s| s.chars()) | |
1154 | /// .flatten() | |
1155 | /// .collect(); | |
1156 | /// assert_eq!(merged, "alphabetagamma"); | |
1157 | /// ``` | |
1158 | /// | |
1159 | /// You can also rewrite this in terms of [`flat_map()`], which is preferable | |
1160 | /// in this case since it conveys intent more clearly: | |
1161 | /// | |
1162 | /// ``` | |
1163 | /// let words = ["alpha", "beta", "gamma"]; | |
1164 | /// | |
1165 | /// // chars() returns an iterator | |
1166 | /// let merged: String = words.iter() | |
1167 | /// .flat_map(|s| s.chars()) | |
1168 | /// .collect(); | |
1169 | /// assert_eq!(merged, "alphabetagamma"); | |
1170 | /// ``` | |
1171 | /// | |
1172 | /// Flattening once only removes one level of nesting: | |
1173 | /// | |
1174 | /// ``` | |
0531ce1d XL |
1175 | /// let d3 = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]; |
1176 | /// | |
1177 | /// let d2 = d3.iter().flatten().collect::<Vec<_>>(); | |
1178 | /// assert_eq!(d2, [&[1, 2], &[3, 4], &[5, 6], &[7, 8]]); | |
1179 | /// | |
1180 | /// let d1 = d3.iter().flatten().flatten().collect::<Vec<_>>(); | |
1181 | /// assert_eq!(d1, [&1, &2, &3, &4, &5, &6, &7, &8]); | |
1182 | /// ``` | |
1183 | /// | |
1184 | /// Here we see that `flatten()` does not perform a "deep" flatten. | |
1185 | /// Instead, only one level of nesting is removed. That is, if you | |
1186 | /// `flatten()` a three-dimensional array the result will be | |
1187 | /// two-dimensional and not one-dimensional. To get a one-dimensional | |
1188 | /// structure, you have to `flatten()` again. | |
83c7162d XL |
1189 | /// |
1190 | /// [`flat_map()`]: #method.flat_map | |
0531ce1d | 1191 | #[inline] |
b7449926 | 1192 | #[stable(feature = "iterator_flatten", since = "1.29.0")] |
0531ce1d XL |
1193 | fn flatten(self) -> Flatten<Self> |
1194 | where Self: Sized, Self::Item: IntoIterator { | |
9fa01778 | 1195 | Flatten::new(self) |
a7813a04 XL |
1196 | } |
1197 | ||
476ff2be SL |
1198 | /// Creates an iterator which ends after the first [`None`]. |
1199 | /// | |
1200 | /// After an iterator returns [`None`], future calls may or may not yield | |
1201 | /// [`Some(T)`] again. `fuse()` adapts an iterator, ensuring that after a | |
1202 | /// [`None`] is given, it will always return [`None`] forever. | |
a7813a04 | 1203 | /// |
476ff2be SL |
1204 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
1205 | /// [`Some(T)`]: ../../std/option/enum.Option.html#variant.Some | |
a7813a04 XL |
1206 | /// |
1207 | /// # Examples | |
1208 | /// | |
1209 | /// Basic usage: | |
1210 | /// | |
1211 | /// ``` | |
1212 | /// // an iterator which alternates between Some and None | |
1213 | /// struct Alternate { | |
1214 | /// state: i32, | |
1215 | /// } | |
1216 | /// | |
1217 | /// impl Iterator for Alternate { | |
1218 | /// type Item = i32; | |
1219 | /// | |
1220 | /// fn next(&mut self) -> Option<i32> { | |
1221 | /// let val = self.state; | |
1222 | /// self.state = self.state + 1; | |
1223 | /// | |
1224 | /// // if it's even, Some(i32), else None | |
1225 | /// if val % 2 == 0 { | |
1226 | /// Some(val) | |
1227 | /// } else { | |
1228 | /// None | |
1229 | /// } | |
1230 | /// } | |
1231 | /// } | |
1232 | /// | |
1233 | /// let mut iter = Alternate { state: 0 }; | |
1234 | /// | |
1235 | /// // we can see our iterator going back and forth | |
1236 | /// assert_eq!(iter.next(), Some(0)); | |
1237 | /// assert_eq!(iter.next(), None); | |
1238 | /// assert_eq!(iter.next(), Some(2)); | |
1239 | /// assert_eq!(iter.next(), None); | |
1240 | /// | |
1241 | /// // however, once we fuse it... | |
1242 | /// let mut iter = iter.fuse(); | |
1243 | /// | |
1244 | /// assert_eq!(iter.next(), Some(4)); | |
1245 | /// assert_eq!(iter.next(), None); | |
1246 | /// | |
9fa01778 | 1247 | /// // it will always return `None` after the first time. |
a7813a04 XL |
1248 | /// assert_eq!(iter.next(), None); |
1249 | /// assert_eq!(iter.next(), None); | |
1250 | /// assert_eq!(iter.next(), None); | |
1251 | /// ``` | |
1252 | #[inline] | |
1253 | #[stable(feature = "rust1", since = "1.0.0")] | |
1254 | fn fuse(self) -> Fuse<Self> where Self: Sized { | |
9fa01778 | 1255 | Fuse::new(self) |
a7813a04 XL |
1256 | } |
1257 | ||
60c5eb7d | 1258 | /// Does something with each element of an iterator, passing the value on. |
a7813a04 XL |
1259 | /// |
1260 | /// When using iterators, you'll often chain several of them together. | |
1261 | /// While working on such code, you might want to check out what's | |
1262 | /// happening at various parts in the pipeline. To do that, insert | |
1263 | /// a call to `inspect()`. | |
1264 | /// | |
94b46f34 XL |
1265 | /// It's more common for `inspect()` to be used as a debugging tool than to |
1266 | /// exist in your final code, but applications may find it useful in certain | |
1267 | /// situations when errors need to be logged before being discarded. | |
a7813a04 XL |
1268 | /// |
1269 | /// # Examples | |
1270 | /// | |
1271 | /// Basic usage: | |
1272 | /// | |
1273 | /// ``` | |
1274 | /// let a = [1, 4, 2, 3]; | |
1275 | /// | |
1276 | /// // this iterator sequence is complex. | |
1277 | /// let sum = a.iter() | |
0531ce1d XL |
1278 | /// .cloned() |
1279 | /// .filter(|x| x % 2 == 0) | |
1280 | /// .fold(0, |sum, i| sum + i); | |
a7813a04 XL |
1281 | /// |
1282 | /// println!("{}", sum); | |
1283 | /// | |
1284 | /// // let's add some inspect() calls to investigate what's happening | |
1285 | /// let sum = a.iter() | |
0531ce1d XL |
1286 | /// .cloned() |
1287 | /// .inspect(|x| println!("about to filter: {}", x)) | |
1288 | /// .filter(|x| x % 2 == 0) | |
1289 | /// .inspect(|x| println!("made it through filter: {}", x)) | |
1290 | /// .fold(0, |sum, i| sum + i); | |
a7813a04 XL |
1291 | /// |
1292 | /// println!("{}", sum); | |
1293 | /// ``` | |
1294 | /// | |
1295 | /// This will print: | |
1296 | /// | |
1297 | /// ```text | |
0531ce1d | 1298 | /// 6 |
a7813a04 XL |
1299 | /// about to filter: 1 |
1300 | /// about to filter: 4 | |
1301 | /// made it through filter: 4 | |
1302 | /// about to filter: 2 | |
1303 | /// made it through filter: 2 | |
1304 | /// about to filter: 3 | |
1305 | /// 6 | |
1306 | /// ``` | |
94b46f34 XL |
1307 | /// |
1308 | /// Logging errors before discarding them: | |
1309 | /// | |
1310 | /// ``` | |
1311 | /// let lines = ["1", "2", "a"]; | |
1312 | /// | |
1313 | /// let sum: i32 = lines | |
1314 | /// .iter() | |
1315 | /// .map(|line| line.parse::<i32>()) | |
1316 | /// .inspect(|num| { | |
1317 | /// if let Err(ref e) = *num { | |
1318 | /// println!("Parsing error: {}", e); | |
1319 | /// } | |
1320 | /// }) | |
1321 | /// .filter_map(Result::ok) | |
1322 | /// .sum(); | |
1323 | /// | |
1324 | /// println!("Sum: {}", sum); | |
1325 | /// ``` | |
1326 | /// | |
1327 | /// This will print: | |
1328 | /// | |
1329 | /// ```text | |
1330 | /// Parsing error: invalid digit found in string | |
1331 | /// Sum: 3 | |
1332 | /// ``` | |
a7813a04 XL |
1333 | #[inline] |
1334 | #[stable(feature = "rust1", since = "1.0.0")] | |
1335 | fn inspect<F>(self, f: F) -> Inspect<Self, F> where | |
1336 | Self: Sized, F: FnMut(&Self::Item), | |
1337 | { | |
9fa01778 | 1338 | Inspect::new(self, f) |
a7813a04 XL |
1339 | } |
1340 | ||
1341 | /// Borrows an iterator, rather than consuming it. | |
1342 | /// | |
1343 | /// This is useful to allow applying iterator adaptors while still | |
1344 | /// retaining ownership of the original iterator. | |
1345 | /// | |
1346 | /// # Examples | |
1347 | /// | |
1348 | /// Basic usage: | |
1349 | /// | |
1350 | /// ``` | |
1351 | /// let a = [1, 2, 3]; | |
1352 | /// | |
48663c56 | 1353 | /// let iter = a.iter(); |
a7813a04 | 1354 | /// |
0531ce1d | 1355 | /// let sum: i32 = iter.take(5).fold(0, |acc, i| acc + i ); |
a7813a04 XL |
1356 | /// |
1357 | /// assert_eq!(sum, 6); | |
1358 | /// | |
1359 | /// // if we try to use iter again, it won't work. The following line | |
1360 | /// // gives "error: use of moved value: `iter` | |
1361 | /// // assert_eq!(iter.next(), None); | |
1362 | /// | |
1363 | /// // let's try that again | |
1364 | /// let a = [1, 2, 3]; | |
1365 | /// | |
48663c56 | 1366 | /// let mut iter = a.iter(); |
a7813a04 XL |
1367 | /// |
1368 | /// // instead, we add in a .by_ref() | |
0531ce1d | 1369 | /// let sum: i32 = iter.by_ref().take(2).fold(0, |acc, i| acc + i ); |
a7813a04 XL |
1370 | /// |
1371 | /// assert_eq!(sum, 3); | |
1372 | /// | |
1373 | /// // now this is just fine: | |
1374 | /// assert_eq!(iter.next(), Some(&3)); | |
1375 | /// assert_eq!(iter.next(), None); | |
1376 | /// ``` | |
1377 | #[stable(feature = "rust1", since = "1.0.0")] | |
1378 | fn by_ref(&mut self) -> &mut Self where Self: Sized { self } | |
1379 | ||
1380 | /// Transforms an iterator into a collection. | |
1381 | /// | |
1382 | /// `collect()` can take anything iterable, and turn it into a relevant | |
1383 | /// collection. This is one of the more powerful methods in the standard | |
1384 | /// library, used in a variety of contexts. | |
1385 | /// | |
1386 | /// The most basic pattern in which `collect()` is used is to turn one | |
cc61c64b | 1387 | /// collection into another. You take a collection, call [`iter`] on it, |
a7813a04 XL |
1388 | /// do a bunch of transformations, and then `collect()` at the end. |
1389 | /// | |
1390 | /// One of the keys to `collect()`'s power is that many things you might | |
1391 | /// not think of as 'collections' actually are. For example, a [`String`] | |
32a655c1 SL |
1392 | /// is a collection of [`char`]s. And a collection of |
1393 | /// [`Result<T, E>`][`Result`] can be thought of as single | |
1394 | /// [`Result`]`<Collection<T>, E>`. See the examples below for more. | |
a7813a04 | 1395 | /// |
a7813a04 XL |
1396 | /// Because `collect()` is so general, it can cause problems with type |
1397 | /// inference. As such, `collect()` is one of the few times you'll see | |
1398 | /// the syntax affectionately known as the 'turbofish': `::<>`. This | |
1399 | /// helps the inference algorithm understand specifically which collection | |
1400 | /// you're trying to collect into. | |
1401 | /// | |
1402 | /// # Examples | |
1403 | /// | |
1404 | /// Basic usage: | |
1405 | /// | |
1406 | /// ``` | |
1407 | /// let a = [1, 2, 3]; | |
1408 | /// | |
1409 | /// let doubled: Vec<i32> = a.iter() | |
1410 | /// .map(|&x| x * 2) | |
1411 | /// .collect(); | |
1412 | /// | |
1413 | /// assert_eq!(vec![2, 4, 6], doubled); | |
1414 | /// ``` | |
1415 | /// | |
1416 | /// Note that we needed the `: Vec<i32>` on the left-hand side. This is because | |
1417 | /// we could collect into, for example, a [`VecDeque<T>`] instead: | |
1418 | /// | |
1419 | /// [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html | |
1420 | /// | |
1421 | /// ``` | |
1422 | /// use std::collections::VecDeque; | |
1423 | /// | |
1424 | /// let a = [1, 2, 3]; | |
1425 | /// | |
0531ce1d | 1426 | /// let doubled: VecDeque<i32> = a.iter().map(|&x| x * 2).collect(); |
a7813a04 XL |
1427 | /// |
1428 | /// assert_eq!(2, doubled[0]); | |
1429 | /// assert_eq!(4, doubled[1]); | |
1430 | /// assert_eq!(6, doubled[2]); | |
1431 | /// ``` | |
1432 | /// | |
1433 | /// Using the 'turbofish' instead of annotating `doubled`: | |
1434 | /// | |
1435 | /// ``` | |
1436 | /// let a = [1, 2, 3]; | |
1437 | /// | |
0531ce1d | 1438 | /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<i32>>(); |
a7813a04 XL |
1439 | /// |
1440 | /// assert_eq!(vec![2, 4, 6], doubled); | |
1441 | /// ``` | |
1442 | /// | |
3b2f2976 | 1443 | /// Because `collect()` only cares about what you're collecting into, you can |
a7813a04 XL |
1444 | /// still use a partial type hint, `_`, with the turbofish: |
1445 | /// | |
1446 | /// ``` | |
1447 | /// let a = [1, 2, 3]; | |
1448 | /// | |
0531ce1d | 1449 | /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<_>>(); |
a7813a04 XL |
1450 | /// |
1451 | /// assert_eq!(vec![2, 4, 6], doubled); | |
1452 | /// ``` | |
1453 | /// | |
1454 | /// Using `collect()` to make a [`String`]: | |
1455 | /// | |
1456 | /// ``` | |
1457 | /// let chars = ['g', 'd', 'k', 'k', 'n']; | |
1458 | /// | |
1459 | /// let hello: String = chars.iter() | |
0531ce1d XL |
1460 | /// .map(|&x| x as u8) |
1461 | /// .map(|x| (x + 1) as char) | |
1462 | /// .collect(); | |
a7813a04 XL |
1463 | /// |
1464 | /// assert_eq!("hello", hello); | |
1465 | /// ``` | |
1466 | /// | |
476ff2be | 1467 | /// If you have a list of [`Result<T, E>`][`Result`]s, you can use `collect()` to |
a7813a04 XL |
1468 | /// see if any of them failed: |
1469 | /// | |
1470 | /// ``` | |
1471 | /// let results = [Ok(1), Err("nope"), Ok(3), Err("bad")]; | |
1472 | /// | |
1473 | /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect(); | |
1474 | /// | |
1475 | /// // gives us the first error | |
1476 | /// assert_eq!(Err("nope"), result); | |
1477 | /// | |
1478 | /// let results = [Ok(1), Ok(3)]; | |
1479 | /// | |
1480 | /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect(); | |
1481 | /// | |
1482 | /// // gives us the list of answers | |
1483 | /// assert_eq!(Ok(vec![1, 3]), result); | |
1484 | /// ``` | |
476ff2be | 1485 | /// |
cc61c64b | 1486 | /// [`iter`]: ../../std/iter/trait.Iterator.html#tymethod.next |
476ff2be SL |
1487 | /// [`String`]: ../../std/string/struct.String.html |
1488 | /// [`char`]: ../../std/primitive.char.html | |
1489 | /// [`Result`]: ../../std/result/enum.Result.html | |
a7813a04 XL |
1490 | #[inline] |
1491 | #[stable(feature = "rust1", since = "1.0.0")] | |
83c7162d | 1492 | #[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"] |
a7813a04 XL |
1493 | fn collect<B: FromIterator<Self::Item>>(self) -> B where Self: Sized { |
1494 | FromIterator::from_iter(self) | |
1495 | } | |
1496 | ||
1497 | /// Consumes an iterator, creating two collections from it. | |
1498 | /// | |
1499 | /// The predicate passed to `partition()` can return `true`, or `false`. | |
1500 | /// `partition()` returns a pair, all of the elements for which it returned | |
1501 | /// `true`, and all of the elements for which it returned `false`. | |
1502 | /// | |
416331ca XL |
1503 | /// See also [`is_partitioned()`] and [`partition_in_place()`]. |
1504 | /// | |
1505 | /// [`is_partitioned()`]: #method.is_partitioned | |
1506 | /// [`partition_in_place()`]: #method.partition_in_place | |
1507 | /// | |
a7813a04 XL |
1508 | /// # Examples |
1509 | /// | |
1510 | /// Basic usage: | |
1511 | /// | |
1512 | /// ``` | |
1513 | /// let a = [1, 2, 3]; | |
1514 | /// | |
0531ce1d | 1515 | /// let (even, odd): (Vec<i32>, Vec<i32>) = a |
48663c56 | 1516 | /// .iter() |
0531ce1d | 1517 | /// .partition(|&n| n % 2 == 0); |
a7813a04 XL |
1518 | /// |
1519 | /// assert_eq!(even, vec![2]); | |
1520 | /// assert_eq!(odd, vec![1, 3]); | |
1521 | /// ``` | |
1522 | #[stable(feature = "rust1", since = "1.0.0")] | |
e1599b0c | 1523 | fn partition<B, F>(self, f: F) -> (B, B) where |
a7813a04 XL |
1524 | Self: Sized, |
1525 | B: Default + Extend<Self::Item>, | |
1526 | F: FnMut(&Self::Item) -> bool | |
1527 | { | |
e1599b0c XL |
1528 | #[inline] |
1529 | fn extend<'a, T, B: Extend<T>>( | |
1530 | mut f: impl FnMut(&T) -> bool + 'a, | |
1531 | left: &'a mut B, | |
1532 | right: &'a mut B, | |
1533 | ) -> impl FnMut(T) + 'a { | |
1534 | move |x| { | |
1535 | if f(&x) { | |
1536 | left.extend(Some(x)); | |
1537 | } else { | |
1538 | right.extend(Some(x)); | |
1539 | } | |
1540 | } | |
1541 | } | |
1542 | ||
a7813a04 XL |
1543 | let mut left: B = Default::default(); |
1544 | let mut right: B = Default::default(); | |
1545 | ||
e1599b0c | 1546 | self.for_each(extend(f, &mut left, &mut right)); |
a7813a04 XL |
1547 | |
1548 | (left, right) | |
1549 | } | |
1550 | ||
60c5eb7d | 1551 | /// Reorders the elements of this iterator *in-place* according to the given predicate, |
416331ca XL |
1552 | /// such that all those that return `true` precede all those that return `false`. |
1553 | /// Returns the number of `true` elements found. | |
1554 | /// | |
1555 | /// The relative order of partitioned items is not maintained. | |
1556 | /// | |
1557 | /// See also [`is_partitioned()`] and [`partition()`]. | |
1558 | /// | |
1559 | /// [`is_partitioned()`]: #method.is_partitioned | |
1560 | /// [`partition()`]: #method.partition | |
1561 | /// | |
1562 | /// # Examples | |
1563 | /// | |
1564 | /// ``` | |
1565 | /// #![feature(iter_partition_in_place)] | |
1566 | /// | |
1567 | /// let mut a = [1, 2, 3, 4, 5, 6, 7]; | |
1568 | /// | |
1569 | /// // Partition in-place between evens and odds | |
1570 | /// let i = a.iter_mut().partition_in_place(|&n| n % 2 == 0); | |
1571 | /// | |
1572 | /// assert_eq!(i, 3); | |
1573 | /// assert!(a[..i].iter().all(|&n| n % 2 == 0)); // evens | |
1574 | /// assert!(a[i..].iter().all(|&n| n % 2 == 1)); // odds | |
1575 | /// ``` | |
1576 | #[unstable(feature = "iter_partition_in_place", reason = "new API", issue = "62543")] | |
1577 | fn partition_in_place<'a, T: 'a, P>(mut self, ref mut predicate: P) -> usize | |
1578 | where | |
1579 | Self: Sized + DoubleEndedIterator<Item = &'a mut T>, | |
1580 | P: FnMut(&T) -> bool, | |
1581 | { | |
1582 | // FIXME: should we worry about the count overflowing? The only way to have more than | |
1583 | // `usize::MAX` mutable references is with ZSTs, which aren't useful to partition... | |
1584 | ||
1585 | // These closure "factory" functions exist to avoid genericity in `Self`. | |
1586 | ||
1587 | #[inline] | |
1588 | fn is_false<'a, T>( | |
1589 | predicate: &'a mut impl FnMut(&T) -> bool, | |
1590 | true_count: &'a mut usize, | |
1591 | ) -> impl FnMut(&&mut T) -> bool + 'a { | |
1592 | move |x| { | |
1593 | let p = predicate(&**x); | |
1594 | *true_count += p as usize; | |
1595 | !p | |
1596 | } | |
1597 | } | |
1598 | ||
1599 | #[inline] | |
1600 | fn is_true<T>( | |
1601 | predicate: &mut impl FnMut(&T) -> bool | |
1602 | ) -> impl FnMut(&&mut T) -> bool + '_ { | |
1603 | move |x| predicate(&**x) | |
1604 | } | |
1605 | ||
1606 | // Repeatedly find the first `false` and swap it with the last `true`. | |
1607 | let mut true_count = 0; | |
1608 | while let Some(head) = self.find(is_false(predicate, &mut true_count)) { | |
1609 | if let Some(tail) = self.rfind(is_true(predicate)) { | |
1610 | crate::mem::swap(head, tail); | |
1611 | true_count += 1; | |
1612 | } else { | |
1613 | break; | |
1614 | } | |
1615 | } | |
1616 | true_count | |
1617 | } | |
1618 | ||
1619 | /// Checks if the elements of this iterator are partitioned according to the given predicate, | |
1620 | /// such that all those that return `true` precede all those that return `false`. | |
1621 | /// | |
1622 | /// See also [`partition()`] and [`partition_in_place()`]. | |
1623 | /// | |
1624 | /// [`partition()`]: #method.partition | |
1625 | /// [`partition_in_place()`]: #method.partition_in_place | |
1626 | /// | |
1627 | /// # Examples | |
1628 | /// | |
1629 | /// ``` | |
1630 | /// #![feature(iter_is_partitioned)] | |
1631 | /// | |
1632 | /// assert!("Iterator".chars().is_partitioned(char::is_uppercase)); | |
1633 | /// assert!(!"IntoIterator".chars().is_partitioned(char::is_uppercase)); | |
1634 | /// ``` | |
1635 | #[unstable(feature = "iter_is_partitioned", reason = "new API", issue = "62544")] | |
1636 | fn is_partitioned<P>(mut self, mut predicate: P) -> bool | |
1637 | where | |
1638 | Self: Sized, | |
1639 | P: FnMut(Self::Item) -> bool, | |
1640 | { | |
1641 | // Either all items test `true`, or the first clause stops at `false` | |
1642 | // and we check that there are no more `true` items after that. | |
1643 | self.all(&mut predicate) || !self.any(predicate) | |
1644 | } | |
1645 | ||
abe05a73 XL |
1646 | /// An iterator method that applies a function as long as it returns |
1647 | /// successfully, producing a single, final value. | |
1648 | /// | |
1649 | /// `try_fold()` takes two arguments: an initial value, and a closure with | |
1650 | /// two arguments: an 'accumulator', and an element. The closure either | |
1651 | /// returns successfully, with the value that the accumulator should have | |
1652 | /// for the next iteration, or it returns failure, with an error value that | |
1653 | /// is propagated back to the caller immediately (short-circuiting). | |
1654 | /// | |
1655 | /// The initial value is the value the accumulator will have on the first | |
9fa01778 | 1656 | /// call. If applying the closure succeeded against every element of the |
abe05a73 XL |
1657 | /// iterator, `try_fold()` returns the final accumulator as success. |
1658 | /// | |
1659 | /// Folding is useful whenever you have a collection of something, and want | |
1660 | /// to produce a single value from it. | |
1661 | /// | |
1662 | /// # Note to Implementors | |
1663 | /// | |
1664 | /// Most of the other (forward) methods have default implementations in | |
1665 | /// terms of this one, so try to implement this explicitly if it can | |
1666 | /// do something better than the default `for` loop implementation. | |
1667 | /// | |
1668 | /// In particular, try to have this call `try_fold()` on the internal parts | |
9fa01778 | 1669 | /// from which this iterator is composed. If multiple calls are needed, |
0531ce1d XL |
1670 | /// the `?` operator may be convenient for chaining the accumulator value |
1671 | /// along, but beware any invariants that need to be upheld before those | |
9fa01778 | 1672 | /// early returns. This is a `&mut self` method, so iteration needs to be |
abe05a73 XL |
1673 | /// resumable after hitting an error here. |
1674 | /// | |
1675 | /// # Examples | |
1676 | /// | |
1677 | /// Basic usage: | |
1678 | /// | |
1679 | /// ``` | |
abe05a73 XL |
1680 | /// let a = [1, 2, 3]; |
1681 | /// | |
1682 | /// // the checked sum of all of the elements of the array | |
0531ce1d | 1683 | /// let sum = a.iter().try_fold(0i8, |acc, &x| acc.checked_add(x)); |
abe05a73 XL |
1684 | /// |
1685 | /// assert_eq!(sum, Some(6)); | |
1686 | /// ``` | |
1687 | /// | |
1688 | /// Short-circuiting: | |
1689 | /// | |
1690 | /// ``` | |
abe05a73 XL |
1691 | /// let a = [10, 20, 30, 100, 40, 50]; |
1692 | /// let mut it = a.iter(); | |
1693 | /// | |
1694 | /// // This sum overflows when adding the 100 element | |
1695 | /// let sum = it.try_fold(0i8, |acc, &x| acc.checked_add(x)); | |
1696 | /// assert_eq!(sum, None); | |
1697 | /// | |
1698 | /// // Because it short-circuited, the remaining elements are still | |
1699 | /// // available through the iterator. | |
1700 | /// assert_eq!(it.len(), 2); | |
1701 | /// assert_eq!(it.next(), Some(&40)); | |
1702 | /// ``` | |
1703 | #[inline] | |
83c7162d | 1704 | #[stable(feature = "iterator_try_fold", since = "1.27.0")] |
abe05a73 XL |
1705 | fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R where |
1706 | Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B> | |
1707 | { | |
1708 | let mut accum = init; | |
1709 | while let Some(x) = self.next() { | |
1710 | accum = f(accum, x)?; | |
1711 | } | |
1712 | Try::from_ok(accum) | |
1713 | } | |
1714 | ||
0531ce1d XL |
1715 | /// An iterator method that applies a fallible function to each item in the |
1716 | /// iterator, stopping at the first error and returning that error. | |
1717 | /// | |
1718 | /// This can also be thought of as the fallible form of [`for_each()`] | |
1719 | /// or as the stateless version of [`try_fold()`]. | |
1720 | /// | |
1721 | /// [`for_each()`]: #method.for_each | |
1722 | /// [`try_fold()`]: #method.try_fold | |
1723 | /// | |
1724 | /// # Examples | |
1725 | /// | |
1726 | /// ``` | |
0531ce1d XL |
1727 | /// use std::fs::rename; |
1728 | /// use std::io::{stdout, Write}; | |
1729 | /// use std::path::Path; | |
1730 | /// | |
1731 | /// let data = ["no_tea.txt", "stale_bread.json", "torrential_rain.png"]; | |
1732 | /// | |
1733 | /// let res = data.iter().try_for_each(|x| writeln!(stdout(), "{}", x)); | |
1734 | /// assert!(res.is_ok()); | |
1735 | /// | |
1736 | /// let mut it = data.iter().cloned(); | |
1737 | /// let res = it.try_for_each(|x| rename(x, Path::new(x).with_extension("old"))); | |
1738 | /// assert!(res.is_err()); | |
1739 | /// // It short-circuited, so the remaining items are still in the iterator: | |
1740 | /// assert_eq!(it.next(), Some("stale_bread.json")); | |
1741 | /// ``` | |
1742 | #[inline] | |
83c7162d | 1743 | #[stable(feature = "iterator_try_fold", since = "1.27.0")] |
e1599b0c | 1744 | fn try_for_each<F, R>(&mut self, f: F) -> R where |
0531ce1d XL |
1745 | Self: Sized, F: FnMut(Self::Item) -> R, R: Try<Ok=()> |
1746 | { | |
e1599b0c XL |
1747 | #[inline] |
1748 | fn call<T, R>(mut f: impl FnMut(T) -> R) -> impl FnMut((), T) -> R { | |
1749 | move |(), x| f(x) | |
1750 | } | |
1751 | ||
1752 | self.try_fold((), call(f)) | |
0531ce1d XL |
1753 | } |
1754 | ||
ea8adc8c | 1755 | /// An iterator method that applies a function, producing a single, final value. |
a7813a04 XL |
1756 | /// |
1757 | /// `fold()` takes two arguments: an initial value, and a closure with two | |
1758 | /// arguments: an 'accumulator', and an element. The closure returns the value that | |
1759 | /// the accumulator should have for the next iteration. | |
1760 | /// | |
1761 | /// The initial value is the value the accumulator will have on the first | |
1762 | /// call. | |
1763 | /// | |
1764 | /// After applying this closure to every element of the iterator, `fold()` | |
1765 | /// returns the accumulator. | |
1766 | /// | |
1767 | /// This operation is sometimes called 'reduce' or 'inject'. | |
1768 | /// | |
1769 | /// Folding is useful whenever you have a collection of something, and want | |
1770 | /// to produce a single value from it. | |
1771 | /// | |
2c00a5a8 XL |
1772 | /// Note: `fold()`, and similar methods that traverse the entire iterator, |
1773 | /// may not terminate for infinite iterators, even on traits for which a | |
1774 | /// result is determinable in finite time. | |
1775 | /// | |
a7813a04 XL |
1776 | /// # Examples |
1777 | /// | |
1778 | /// Basic usage: | |
1779 | /// | |
1780 | /// ``` | |
1781 | /// let a = [1, 2, 3]; | |
1782 | /// | |
abe05a73 | 1783 | /// // the sum of all of the elements of the array |
0531ce1d | 1784 | /// let sum = a.iter().fold(0, |acc, x| acc + x); |
a7813a04 XL |
1785 | /// |
1786 | /// assert_eq!(sum, 6); | |
1787 | /// ``` | |
1788 | /// | |
1789 | /// Let's walk through each step of the iteration here: | |
1790 | /// | |
1791 | /// | element | acc | x | result | | |
1792 | /// |---------|-----|---|--------| | |
1793 | /// | | 0 | | | | |
1794 | /// | 1 | 0 | 1 | 1 | | |
1795 | /// | 2 | 1 | 2 | 3 | | |
1796 | /// | 3 | 3 | 3 | 6 | | |
1797 | /// | |
1798 | /// And so, our final result, `6`. | |
1799 | /// | |
1800 | /// It's common for people who haven't used iterators a lot to | |
1801 | /// use a `for` loop with a list of things to build up a result. Those | |
1802 | /// can be turned into `fold()`s: | |
1803 | /// | |
13cf67c4 | 1804 | /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for |
476ff2be | 1805 | /// |
a7813a04 XL |
1806 | /// ``` |
1807 | /// let numbers = [1, 2, 3, 4, 5]; | |
1808 | /// | |
1809 | /// let mut result = 0; | |
1810 | /// | |
1811 | /// // for loop: | |
1812 | /// for i in &numbers { | |
1813 | /// result = result + i; | |
1814 | /// } | |
1815 | /// | |
1816 | /// // fold: | |
1817 | /// let result2 = numbers.iter().fold(0, |acc, &x| acc + x); | |
1818 | /// | |
1819 | /// // they're the same | |
1820 | /// assert_eq!(result, result2); | |
1821 | /// ``` | |
1822 | #[inline] | |
1823 | #[stable(feature = "rust1", since = "1.0.0")] | |
e1599b0c | 1824 | fn fold<B, F>(mut self, init: B, f: F) -> B where |
a7813a04 XL |
1825 | Self: Sized, F: FnMut(B, Self::Item) -> B, |
1826 | { | |
e1599b0c XL |
1827 | #[inline] |
1828 | fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> { | |
1829 | move |acc, x| Ok(f(acc, x)) | |
1830 | } | |
1831 | ||
1832 | self.try_fold(init, ok(f)).unwrap() | |
a7813a04 XL |
1833 | } |
1834 | ||
1835 | /// Tests if every element of the iterator matches a predicate. | |
1836 | /// | |
1837 | /// `all()` takes a closure that returns `true` or `false`. It applies | |
1838 | /// this closure to each element of the iterator, and if they all return | |
1839 | /// `true`, then so does `all()`. If any of them return `false`, it | |
1840 | /// returns `false`. | |
1841 | /// | |
1842 | /// `all()` is short-circuiting; in other words, it will stop processing | |
1843 | /// as soon as it finds a `false`, given that no matter what else happens, | |
1844 | /// the result will also be `false`. | |
1845 | /// | |
1846 | /// An empty iterator returns `true`. | |
1847 | /// | |
1848 | /// # Examples | |
1849 | /// | |
1850 | /// Basic usage: | |
1851 | /// | |
1852 | /// ``` | |
1853 | /// let a = [1, 2, 3]; | |
1854 | /// | |
1855 | /// assert!(a.iter().all(|&x| x > 0)); | |
1856 | /// | |
1857 | /// assert!(!a.iter().all(|&x| x > 2)); | |
1858 | /// ``` | |
1859 | /// | |
1860 | /// Stopping at the first `false`: | |
1861 | /// | |
1862 | /// ``` | |
1863 | /// let a = [1, 2, 3]; | |
1864 | /// | |
1865 | /// let mut iter = a.iter(); | |
1866 | /// | |
1867 | /// assert!(!iter.all(|&x| x != 2)); | |
1868 | /// | |
1869 | /// // we can still use `iter`, as there are more elements. | |
1870 | /// assert_eq!(iter.next(), Some(&3)); | |
1871 | /// ``` | |
1872 | #[inline] | |
1873 | #[stable(feature = "rust1", since = "1.0.0")] | |
e1599b0c | 1874 | fn all<F>(&mut self, f: F) -> bool where |
a7813a04 XL |
1875 | Self: Sized, F: FnMut(Self::Item) -> bool |
1876 | { | |
e1599b0c | 1877 | #[inline] |
e74abb32 XL |
1878 | fn check<T>(mut f: impl FnMut(T) -> bool) -> impl FnMut((), T) -> LoopState<(), ()> { |
1879 | move |(), x| { | |
e1599b0c XL |
1880 | if f(x) { LoopState::Continue(()) } |
1881 | else { LoopState::Break(()) } | |
1882 | } | |
1883 | } | |
e74abb32 | 1884 | self.try_fold((), check(f)) == LoopState::Continue(()) |
a7813a04 XL |
1885 | } |
1886 | ||
1887 | /// Tests if any element of the iterator matches a predicate. | |
1888 | /// | |
1889 | /// `any()` takes a closure that returns `true` or `false`. It applies | |
1890 | /// this closure to each element of the iterator, and if any of them return | |
1891 | /// `true`, then so does `any()`. If they all return `false`, it | |
1892 | /// returns `false`. | |
1893 | /// | |
1894 | /// `any()` is short-circuiting; in other words, it will stop processing | |
1895 | /// as soon as it finds a `true`, given that no matter what else happens, | |
1896 | /// the result will also be `true`. | |
1897 | /// | |
1898 | /// An empty iterator returns `false`. | |
1899 | /// | |
1900 | /// # Examples | |
1901 | /// | |
1902 | /// Basic usage: | |
1903 | /// | |
1904 | /// ``` | |
1905 | /// let a = [1, 2, 3]; | |
1906 | /// | |
1907 | /// assert!(a.iter().any(|&x| x > 0)); | |
1908 | /// | |
1909 | /// assert!(!a.iter().any(|&x| x > 5)); | |
1910 | /// ``` | |
1911 | /// | |
1912 | /// Stopping at the first `true`: | |
1913 | /// | |
1914 | /// ``` | |
1915 | /// let a = [1, 2, 3]; | |
1916 | /// | |
1917 | /// let mut iter = a.iter(); | |
1918 | /// | |
1919 | /// assert!(iter.any(|&x| x != 2)); | |
1920 | /// | |
1921 | /// // we can still use `iter`, as there are more elements. | |
1922 | /// assert_eq!(iter.next(), Some(&2)); | |
1923 | /// ``` | |
1924 | #[inline] | |
1925 | #[stable(feature = "rust1", since = "1.0.0")] | |
e1599b0c | 1926 | fn any<F>(&mut self, f: F) -> bool where |
a7813a04 XL |
1927 | Self: Sized, |
1928 | F: FnMut(Self::Item) -> bool | |
1929 | { | |
e1599b0c | 1930 | #[inline] |
e74abb32 XL |
1931 | fn check<T>(mut f: impl FnMut(T) -> bool) -> impl FnMut((), T) -> LoopState<(), ()> { |
1932 | move |(), x| { | |
e1599b0c XL |
1933 | if f(x) { LoopState::Break(()) } |
1934 | else { LoopState::Continue(()) } | |
1935 | } | |
1936 | } | |
1937 | ||
e74abb32 | 1938 | self.try_fold((), check(f)) == LoopState::Break(()) |
a7813a04 XL |
1939 | } |
1940 | ||
1941 | /// Searches for an element of an iterator that satisfies a predicate. | |
1942 | /// | |
1943 | /// `find()` takes a closure that returns `true` or `false`. It applies | |
1944 | /// this closure to each element of the iterator, and if any of them return | |
476ff2be SL |
1945 | /// `true`, then `find()` returns [`Some(element)`]. If they all return |
1946 | /// `false`, it returns [`None`]. | |
a7813a04 XL |
1947 | /// |
1948 | /// `find()` is short-circuiting; in other words, it will stop processing | |
1949 | /// as soon as the closure returns `true`. | |
1950 | /// | |
1951 | /// Because `find()` takes a reference, and many iterators iterate over | |
1952 | /// references, this leads to a possibly confusing situation where the | |
1953 | /// argument is a double reference. You can see this effect in the | |
1954 | /// examples below, with `&&x`. | |
1955 | /// | |
476ff2be SL |
1956 | /// [`Some(element)`]: ../../std/option/enum.Option.html#variant.Some |
1957 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
1958 | /// | |
a7813a04 XL |
1959 | /// # Examples |
1960 | /// | |
1961 | /// Basic usage: | |
1962 | /// | |
1963 | /// ``` | |
1964 | /// let a = [1, 2, 3]; | |
1965 | /// | |
1966 | /// assert_eq!(a.iter().find(|&&x| x == 2), Some(&2)); | |
1967 | /// | |
1968 | /// assert_eq!(a.iter().find(|&&x| x == 5), None); | |
1969 | /// ``` | |
1970 | /// | |
1971 | /// Stopping at the first `true`: | |
1972 | /// | |
1973 | /// ``` | |
1974 | /// let a = [1, 2, 3]; | |
1975 | /// | |
1976 | /// let mut iter = a.iter(); | |
1977 | /// | |
1978 | /// assert_eq!(iter.find(|&&x| x == 2), Some(&2)); | |
1979 | /// | |
1980 | /// // we can still use `iter`, as there are more elements. | |
1981 | /// assert_eq!(iter.next(), Some(&3)); | |
1982 | /// ``` | |
1983 | #[inline] | |
1984 | #[stable(feature = "rust1", since = "1.0.0")] | |
e1599b0c | 1985 | fn find<P>(&mut self, predicate: P) -> Option<Self::Item> where |
a7813a04 XL |
1986 | Self: Sized, |
1987 | P: FnMut(&Self::Item) -> bool, | |
1988 | { | |
e1599b0c | 1989 | #[inline] |
e74abb32 XL |
1990 | fn check<T>( |
1991 | mut predicate: impl FnMut(&T) -> bool | |
1992 | ) -> impl FnMut((), T) -> LoopState<(), T> { | |
1993 | move |(), x| { | |
e1599b0c XL |
1994 | if predicate(&x) { LoopState::Break(x) } |
1995 | else { LoopState::Continue(()) } | |
1996 | } | |
1997 | } | |
1998 | ||
e74abb32 | 1999 | self.try_fold((), check(predicate)).break_value() |
a7813a04 XL |
2000 | } |
2001 | ||
83c7162d XL |
2002 | /// Applies function to the elements of iterator and returns |
2003 | /// the first non-none result. | |
2004 | /// | |
2005 | /// `iter.find_map(f)` is equivalent to `iter.filter_map(f).next()`. | |
2006 | /// | |
2007 | /// | |
2008 | /// # Examples | |
2009 | /// | |
2010 | /// ``` | |
83c7162d XL |
2011 | /// let a = ["lol", "NaN", "2", "5"]; |
2012 | /// | |
a1dfa0c6 | 2013 | /// let first_number = a.iter().find_map(|s| s.parse().ok()); |
83c7162d XL |
2014 | /// |
2015 | /// assert_eq!(first_number, Some(2)); | |
2016 | /// ``` | |
2017 | #[inline] | |
b7449926 | 2018 | #[stable(feature = "iterator_find_map", since = "1.30.0")] |
e1599b0c | 2019 | fn find_map<B, F>(&mut self, f: F) -> Option<B> where |
83c7162d XL |
2020 | Self: Sized, |
2021 | F: FnMut(Self::Item) -> Option<B>, | |
2022 | { | |
e1599b0c | 2023 | #[inline] |
e74abb32 XL |
2024 | fn check<T, B>(mut f: impl FnMut(T) -> Option<B>) -> impl FnMut((), T) -> LoopState<(), B> { |
2025 | move |(), x| match f(x) { | |
83c7162d XL |
2026 | Some(x) => LoopState::Break(x), |
2027 | None => LoopState::Continue(()), | |
2028 | } | |
e1599b0c XL |
2029 | } |
2030 | ||
e74abb32 | 2031 | self.try_fold((), check(f)).break_value() |
83c7162d XL |
2032 | } |
2033 | ||
a7813a04 XL |
2034 | /// Searches for an element in an iterator, returning its index. |
2035 | /// | |
2036 | /// `position()` takes a closure that returns `true` or `false`. It applies | |
2037 | /// this closure to each element of the iterator, and if one of them | |
476ff2be SL |
2038 | /// returns `true`, then `position()` returns [`Some(index)`]. If all of |
2039 | /// them return `false`, it returns [`None`]. | |
a7813a04 XL |
2040 | /// |
2041 | /// `position()` is short-circuiting; in other words, it will stop | |
2042 | /// processing as soon as it finds a `true`. | |
2043 | /// | |
2044 | /// # Overflow Behavior | |
2045 | /// | |
2046 | /// The method does no guarding against overflows, so if there are more | |
476ff2be | 2047 | /// than [`usize::MAX`] non-matching elements, it either produces the wrong |
a7813a04 XL |
2048 | /// result or panics. If debug assertions are enabled, a panic is |
2049 | /// guaranteed. | |
2050 | /// | |
2051 | /// # Panics | |
2052 | /// | |
2053 | /// This function might panic if the iterator has more than `usize::MAX` | |
2054 | /// non-matching elements. | |
2055 | /// | |
476ff2be SL |
2056 | /// [`Some(index)`]: ../../std/option/enum.Option.html#variant.Some |
2057 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
2058 | /// [`usize::MAX`]: ../../std/usize/constant.MAX.html | |
2059 | /// | |
a7813a04 XL |
2060 | /// # Examples |
2061 | /// | |
2062 | /// Basic usage: | |
2063 | /// | |
2064 | /// ``` | |
2065 | /// let a = [1, 2, 3]; | |
2066 | /// | |
2067 | /// assert_eq!(a.iter().position(|&x| x == 2), Some(1)); | |
2068 | /// | |
2069 | /// assert_eq!(a.iter().position(|&x| x == 5), None); | |
2070 | /// ``` | |
2071 | /// | |
2072 | /// Stopping at the first `true`: | |
2073 | /// | |
2074 | /// ``` | |
cc61c64b | 2075 | /// let a = [1, 2, 3, 4]; |
a7813a04 XL |
2076 | /// |
2077 | /// let mut iter = a.iter(); | |
2078 | /// | |
cc61c64b | 2079 | /// assert_eq!(iter.position(|&x| x >= 2), Some(1)); |
a7813a04 XL |
2080 | /// |
2081 | /// // we can still use `iter`, as there are more elements. | |
2082 | /// assert_eq!(iter.next(), Some(&3)); | |
cc61c64b XL |
2083 | /// |
2084 | /// // The returned index depends on iterator state | |
2085 | /// assert_eq!(iter.position(|&x| x == 4), Some(0)); | |
2086 | /// | |
a7813a04 XL |
2087 | /// ``` |
2088 | #[inline] | |
2089 | #[stable(feature = "rust1", since = "1.0.0")] | |
e1599b0c | 2090 | fn position<P>(&mut self, predicate: P) -> Option<usize> where |
a7813a04 XL |
2091 | Self: Sized, |
2092 | P: FnMut(Self::Item) -> bool, | |
2093 | { | |
e1599b0c XL |
2094 | #[inline] |
2095 | fn check<T>( | |
2096 | mut predicate: impl FnMut(T) -> bool, | |
2097 | ) -> impl FnMut(usize, T) -> LoopState<usize, usize> { | |
2098 | // The addition might panic on overflow | |
2099 | move |i, x| { | |
2100 | if predicate(x) { LoopState::Break(i) } | |
2101 | else { LoopState::Continue(Add::add(i, 1)) } | |
2102 | } | |
2103 | } | |
2104 | ||
2105 | self.try_fold(0, check(predicate)).break_value() | |
a7813a04 XL |
2106 | } |
2107 | ||
2108 | /// Searches for an element in an iterator from the right, returning its | |
2109 | /// index. | |
2110 | /// | |
2111 | /// `rposition()` takes a closure that returns `true` or `false`. It applies | |
2112 | /// this closure to each element of the iterator, starting from the end, | |
2113 | /// and if one of them returns `true`, then `rposition()` returns | |
476ff2be | 2114 | /// [`Some(index)`]. If all of them return `false`, it returns [`None`]. |
a7813a04 XL |
2115 | /// |
2116 | /// `rposition()` is short-circuiting; in other words, it will stop | |
2117 | /// processing as soon as it finds a `true`. | |
2118 | /// | |
476ff2be SL |
2119 | /// [`Some(index)`]: ../../std/option/enum.Option.html#variant.Some |
2120 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
2121 | /// | |
a7813a04 XL |
2122 | /// # Examples |
2123 | /// | |
2124 | /// Basic usage: | |
2125 | /// | |
2126 | /// ``` | |
2127 | /// let a = [1, 2, 3]; | |
2128 | /// | |
2129 | /// assert_eq!(a.iter().rposition(|&x| x == 3), Some(2)); | |
2130 | /// | |
2131 | /// assert_eq!(a.iter().rposition(|&x| x == 5), None); | |
2132 | /// ``` | |
2133 | /// | |
2134 | /// Stopping at the first `true`: | |
2135 | /// | |
2136 | /// ``` | |
2137 | /// let a = [1, 2, 3]; | |
2138 | /// | |
2139 | /// let mut iter = a.iter(); | |
2140 | /// | |
2141 | /// assert_eq!(iter.rposition(|&x| x == 2), Some(1)); | |
2142 | /// | |
2143 | /// // we can still use `iter`, as there are more elements. | |
2144 | /// assert_eq!(iter.next(), Some(&1)); | |
2145 | /// ``` | |
2146 | #[inline] | |
2147 | #[stable(feature = "rust1", since = "1.0.0")] | |
e1599b0c | 2148 | fn rposition<P>(&mut self, predicate: P) -> Option<usize> where |
a7813a04 XL |
2149 | P: FnMut(Self::Item) -> bool, |
2150 | Self: Sized + ExactSizeIterator + DoubleEndedIterator | |
2151 | { | |
abe05a73 XL |
2152 | // No need for an overflow check here, because `ExactSizeIterator` |
2153 | // implies that the number of elements fits into a `usize`. | |
e1599b0c XL |
2154 | #[inline] |
2155 | fn check<T>( | |
2156 | mut predicate: impl FnMut(T) -> bool, | |
2157 | ) -> impl FnMut(usize, T) -> LoopState<usize, usize> { | |
2158 | move |i, x| { | |
2159 | let i = i - 1; | |
2160 | if predicate(x) { LoopState::Break(i) } | |
2161 | else { LoopState::Continue(i) } | |
2162 | } | |
2163 | } | |
2164 | ||
abe05a73 | 2165 | let n = self.len(); |
e1599b0c | 2166 | self.try_rfold(n, check(predicate)).break_value() |
a7813a04 XL |
2167 | } |
2168 | ||
2169 | /// Returns the maximum element of an iterator. | |
2170 | /// | |
32a655c1 | 2171 | /// If several elements are equally maximum, the last element is |
8bb4bdeb XL |
2172 | /// returned. If the iterator is empty, [`None`] is returned. |
2173 | /// | |
2174 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
a7813a04 XL |
2175 | /// |
2176 | /// # Examples | |
2177 | /// | |
2178 | /// Basic usage: | |
2179 | /// | |
2180 | /// ``` | |
2181 | /// let a = [1, 2, 3]; | |
8bb4bdeb | 2182 | /// let b: Vec<u32> = Vec::new(); |
a7813a04 XL |
2183 | /// |
2184 | /// assert_eq!(a.iter().max(), Some(&3)); | |
8bb4bdeb | 2185 | /// assert_eq!(b.iter().max(), None); |
a7813a04 XL |
2186 | /// ``` |
2187 | #[inline] | |
2188 | #[stable(feature = "rust1", since = "1.0.0")] | |
2189 | fn max(self) -> Option<Self::Item> where Self: Sized, Self::Item: Ord | |
2190 | { | |
532ac7d7 | 2191 | self.max_by(Ord::cmp) |
a7813a04 XL |
2192 | } |
2193 | ||
2194 | /// Returns the minimum element of an iterator. | |
2195 | /// | |
32a655c1 | 2196 | /// If several elements are equally minimum, the first element is |
8bb4bdeb XL |
2197 | /// returned. If the iterator is empty, [`None`] is returned. |
2198 | /// | |
2199 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
a7813a04 XL |
2200 | /// |
2201 | /// # Examples | |
2202 | /// | |
2203 | /// Basic usage: | |
2204 | /// | |
2205 | /// ``` | |
2206 | /// let a = [1, 2, 3]; | |
8bb4bdeb | 2207 | /// let b: Vec<u32> = Vec::new(); |
a7813a04 XL |
2208 | /// |
2209 | /// assert_eq!(a.iter().min(), Some(&1)); | |
8bb4bdeb | 2210 | /// assert_eq!(b.iter().min(), None); |
a7813a04 XL |
2211 | /// ``` |
2212 | #[inline] | |
2213 | #[stable(feature = "rust1", since = "1.0.0")] | |
2214 | fn min(self) -> Option<Self::Item> where Self: Sized, Self::Item: Ord | |
2215 | { | |
532ac7d7 | 2216 | self.min_by(Ord::cmp) |
a7813a04 XL |
2217 | } |
2218 | ||
2219 | /// Returns the element that gives the maximum value from the | |
2220 | /// specified function. | |
2221 | /// | |
32a655c1 | 2222 | /// If several elements are equally maximum, the last element is |
8bb4bdeb XL |
2223 | /// returned. If the iterator is empty, [`None`] is returned. |
2224 | /// | |
2225 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
a7813a04 XL |
2226 | /// |
2227 | /// # Examples | |
2228 | /// | |
2229 | /// ``` | |
2230 | /// let a = [-3_i32, 0, 1, 5, -10]; | |
2231 | /// assert_eq!(*a.iter().max_by_key(|x| x.abs()).unwrap(), -10); | |
2232 | /// ``` | |
2233 | #[inline] | |
2234 | #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] | |
e1599b0c | 2235 | fn max_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item> |
a7813a04 XL |
2236 | where Self: Sized, F: FnMut(&Self::Item) -> B, |
2237 | { | |
e1599b0c XL |
2238 | #[inline] |
2239 | fn key<T, B>(mut f: impl FnMut(&T) -> B) -> impl FnMut(T) -> (B, T) { | |
2240 | move |x| (f(&x), x) | |
2241 | } | |
2242 | ||
2243 | #[inline] | |
2244 | fn compare<T, B: Ord>((x_p, _): &(B, T), (y_p, _): &(B, T)) -> Ordering { | |
2245 | x_p.cmp(y_p) | |
2246 | } | |
2247 | ||
2248 | let (_, x) = self.map(key(f)).max_by(compare)?; | |
2249 | Some(x) | |
a7813a04 XL |
2250 | } |
2251 | ||
9e0c209e SL |
2252 | /// Returns the element that gives the maximum value with respect to the |
2253 | /// specified comparison function. | |
2254 | /// | |
32a655c1 | 2255 | /// If several elements are equally maximum, the last element is |
8bb4bdeb XL |
2256 | /// returned. If the iterator is empty, [`None`] is returned. |
2257 | /// | |
2258 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
9e0c209e SL |
2259 | /// |
2260 | /// # Examples | |
2261 | /// | |
2262 | /// ``` | |
9e0c209e SL |
2263 | /// let a = [-3_i32, 0, 1, 5, -10]; |
2264 | /// assert_eq!(*a.iter().max_by(|x, y| x.cmp(y)).unwrap(), 5); | |
2265 | /// ``` | |
2266 | #[inline] | |
476ff2be | 2267 | #[stable(feature = "iter_max_by", since = "1.15.0")] |
e1599b0c | 2268 | fn max_by<F>(self, compare: F) -> Option<Self::Item> |
9e0c209e SL |
2269 | where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering, |
2270 | { | |
e1599b0c XL |
2271 | #[inline] |
2272 | fn fold<T>(mut compare: impl FnMut(&T, &T) -> Ordering) -> impl FnMut(T, T) -> T { | |
2273 | move |x, y| cmp::max_by(x, y, &mut compare) | |
2274 | } | |
2275 | ||
2276 | fold1(self, fold(compare)) | |
9e0c209e SL |
2277 | } |
2278 | ||
a7813a04 XL |
2279 | /// Returns the element that gives the minimum value from the |
2280 | /// specified function. | |
2281 | /// | |
32a655c1 | 2282 | /// If several elements are equally minimum, the first element is |
8bb4bdeb XL |
2283 | /// returned. If the iterator is empty, [`None`] is returned. |
2284 | /// | |
2285 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
a7813a04 XL |
2286 | /// |
2287 | /// # Examples | |
2288 | /// | |
2289 | /// ``` | |
2290 | /// let a = [-3_i32, 0, 1, 5, -10]; | |
2291 | /// assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0); | |
2292 | /// ``` | |
e1599b0c | 2293 | #[inline] |
a7813a04 | 2294 | #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] |
e1599b0c | 2295 | fn min_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item> |
a7813a04 XL |
2296 | where Self: Sized, F: FnMut(&Self::Item) -> B, |
2297 | { | |
e1599b0c XL |
2298 | #[inline] |
2299 | fn key<T, B>(mut f: impl FnMut(&T) -> B) -> impl FnMut(T) -> (B, T) { | |
2300 | move |x| (f(&x), x) | |
2301 | } | |
2302 | ||
2303 | #[inline] | |
2304 | fn compare<T, B: Ord>((x_p, _): &(B, T), (y_p, _): &(B, T)) -> Ordering { | |
2305 | x_p.cmp(y_p) | |
2306 | } | |
2307 | ||
2308 | let (_, x) = self.map(key(f)).min_by(compare)?; | |
2309 | Some(x) | |
a7813a04 XL |
2310 | } |
2311 | ||
9e0c209e SL |
2312 | /// Returns the element that gives the minimum value with respect to the |
2313 | /// specified comparison function. | |
2314 | /// | |
32a655c1 | 2315 | /// If several elements are equally minimum, the first element is |
8bb4bdeb XL |
2316 | /// returned. If the iterator is empty, [`None`] is returned. |
2317 | /// | |
2318 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
9e0c209e SL |
2319 | /// |
2320 | /// # Examples | |
2321 | /// | |
2322 | /// ``` | |
9e0c209e SL |
2323 | /// let a = [-3_i32, 0, 1, 5, -10]; |
2324 | /// assert_eq!(*a.iter().min_by(|x, y| x.cmp(y)).unwrap(), -10); | |
2325 | /// ``` | |
2326 | #[inline] | |
476ff2be | 2327 | #[stable(feature = "iter_min_by", since = "1.15.0")] |
e1599b0c | 2328 | fn min_by<F>(self, compare: F) -> Option<Self::Item> |
9e0c209e SL |
2329 | where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering, |
2330 | { | |
e1599b0c XL |
2331 | #[inline] |
2332 | fn fold<T>(mut compare: impl FnMut(&T, &T) -> Ordering) -> impl FnMut(T, T) -> T { | |
2333 | move |x, y| cmp::min_by(x, y, &mut compare) | |
2334 | } | |
2335 | ||
2336 | fold1(self, fold(compare)) | |
9e0c209e SL |
2337 | } |
2338 | ||
2339 | ||
a7813a04 XL |
2340 | /// Reverses an iterator's direction. |
2341 | /// | |
2342 | /// Usually, iterators iterate from left to right. After using `rev()`, | |
2343 | /// an iterator will instead iterate from right to left. | |
2344 | /// | |
2345 | /// This is only possible if the iterator has an end, so `rev()` only | |
2346 | /// works on [`DoubleEndedIterator`]s. | |
2347 | /// | |
2348 | /// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html | |
2349 | /// | |
2350 | /// # Examples | |
2351 | /// | |
2352 | /// ``` | |
2353 | /// let a = [1, 2, 3]; | |
2354 | /// | |
2355 | /// let mut iter = a.iter().rev(); | |
2356 | /// | |
2357 | /// assert_eq!(iter.next(), Some(&3)); | |
2358 | /// assert_eq!(iter.next(), Some(&2)); | |
2359 | /// assert_eq!(iter.next(), Some(&1)); | |
2360 | /// | |
2361 | /// assert_eq!(iter.next(), None); | |
2362 | /// ``` | |
2363 | #[inline] | |
2364 | #[stable(feature = "rust1", since = "1.0.0")] | |
2365 | fn rev(self) -> Rev<Self> where Self: Sized + DoubleEndedIterator { | |
9fa01778 | 2366 | Rev::new(self) |
a7813a04 XL |
2367 | } |
2368 | ||
2369 | /// Converts an iterator of pairs into a pair of containers. | |
2370 | /// | |
2371 | /// `unzip()` consumes an entire iterator of pairs, producing two | |
2372 | /// collections: one from the left elements of the pairs, and one | |
2373 | /// from the right elements. | |
2374 | /// | |
cc61c64b | 2375 | /// This function is, in some sense, the opposite of [`zip`]. |
a7813a04 | 2376 | /// |
cc61c64b | 2377 | /// [`zip`]: #method.zip |
a7813a04 XL |
2378 | /// |
2379 | /// # Examples | |
2380 | /// | |
2381 | /// Basic usage: | |
2382 | /// | |
2383 | /// ``` | |
2384 | /// let a = [(1, 2), (3, 4)]; | |
2385 | /// | |
2386 | /// let (left, right): (Vec<_>, Vec<_>) = a.iter().cloned().unzip(); | |
2387 | /// | |
2388 | /// assert_eq!(left, [1, 3]); | |
2389 | /// assert_eq!(right, [2, 4]); | |
2390 | /// ``` | |
2391 | #[stable(feature = "rust1", since = "1.0.0")] | |
2392 | fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where | |
2393 | FromA: Default + Extend<A>, | |
2394 | FromB: Default + Extend<B>, | |
2395 | Self: Sized + Iterator<Item=(A, B)>, | |
2396 | { | |
e1599b0c XL |
2397 | fn extend<'a, A, B>( |
2398 | ts: &'a mut impl Extend<A>, | |
2399 | us: &'a mut impl Extend<B>, | |
2400 | ) -> impl FnMut((A, B)) + 'a { | |
2401 | move |(t, u)| { | |
2402 | ts.extend(Some(t)); | |
2403 | us.extend(Some(u)); | |
2404 | } | |
2405 | } | |
2406 | ||
a7813a04 XL |
2407 | let mut ts: FromA = Default::default(); |
2408 | let mut us: FromB = Default::default(); | |
2409 | ||
e1599b0c | 2410 | self.for_each(extend(&mut ts, &mut us)); |
a7813a04 XL |
2411 | |
2412 | (ts, us) | |
2413 | } | |
2414 | ||
0731742a XL |
2415 | /// Creates an iterator which copies all of its elements. |
2416 | /// | |
2417 | /// This is useful when you have an iterator over `&T`, but you need an | |
2418 | /// iterator over `T`. | |
2419 | /// | |
2420 | /// # Examples | |
2421 | /// | |
2422 | /// Basic usage: | |
2423 | /// | |
2424 | /// ``` | |
0731742a XL |
2425 | /// let a = [1, 2, 3]; |
2426 | /// | |
2427 | /// let v_cloned: Vec<_> = a.iter().copied().collect(); | |
2428 | /// | |
2429 | /// // copied is the same as .map(|&x| x) | |
2430 | /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); | |
2431 | /// | |
2432 | /// assert_eq!(v_cloned, vec![1, 2, 3]); | |
2433 | /// assert_eq!(v_map, vec![1, 2, 3]); | |
2434 | /// ``` | |
48663c56 | 2435 | #[stable(feature = "iter_copied", since = "1.36.0")] |
0731742a XL |
2436 | fn copied<'a, T: 'a>(self) -> Copied<Self> |
2437 | where Self: Sized + Iterator<Item=&'a T>, T: Copy | |
2438 | { | |
9fa01778 | 2439 | Copied::new(self) |
0731742a XL |
2440 | } |
2441 | ||
cc61c64b | 2442 | /// Creates an iterator which [`clone`]s all of its elements. |
a7813a04 XL |
2443 | /// |
2444 | /// This is useful when you have an iterator over `&T`, but you need an | |
2445 | /// iterator over `T`. | |
2446 | /// | |
cc61c64b | 2447 | /// [`clone`]: ../../std/clone/trait.Clone.html#tymethod.clone |
476ff2be | 2448 | /// |
a7813a04 XL |
2449 | /// # Examples |
2450 | /// | |
2451 | /// Basic usage: | |
2452 | /// | |
2453 | /// ``` | |
2454 | /// let a = [1, 2, 3]; | |
2455 | /// | |
2456 | /// let v_cloned: Vec<_> = a.iter().cloned().collect(); | |
2457 | /// | |
2458 | /// // cloned is the same as .map(|&x| x), for integers | |
2459 | /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); | |
2460 | /// | |
2461 | /// assert_eq!(v_cloned, vec![1, 2, 3]); | |
2462 | /// assert_eq!(v_map, vec![1, 2, 3]); | |
2463 | /// ``` | |
2464 | #[stable(feature = "rust1", since = "1.0.0")] | |
2465 | fn cloned<'a, T: 'a>(self) -> Cloned<Self> | |
2466 | where Self: Sized + Iterator<Item=&'a T>, T: Clone | |
2467 | { | |
9fa01778 | 2468 | Cloned::new(self) |
a7813a04 XL |
2469 | } |
2470 | ||
2471 | /// Repeats an iterator endlessly. | |
2472 | /// | |
476ff2be | 2473 | /// Instead of stopping at [`None`], the iterator will instead start again, |
a7813a04 XL |
2474 | /// from the beginning. After iterating again, it will start at the |
2475 | /// beginning again. And again. And again. Forever. | |
2476 | /// | |
476ff2be SL |
2477 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
2478 | /// | |
a7813a04 XL |
2479 | /// # Examples |
2480 | /// | |
2481 | /// Basic usage: | |
2482 | /// | |
2483 | /// ``` | |
2484 | /// let a = [1, 2, 3]; | |
2485 | /// | |
2486 | /// let mut it = a.iter().cycle(); | |
2487 | /// | |
2488 | /// assert_eq!(it.next(), Some(&1)); | |
2489 | /// assert_eq!(it.next(), Some(&2)); | |
2490 | /// assert_eq!(it.next(), Some(&3)); | |
2491 | /// assert_eq!(it.next(), Some(&1)); | |
2492 | /// assert_eq!(it.next(), Some(&2)); | |
2493 | /// assert_eq!(it.next(), Some(&3)); | |
2494 | /// assert_eq!(it.next(), Some(&1)); | |
2495 | /// ``` | |
2496 | #[stable(feature = "rust1", since = "1.0.0")] | |
2497 | #[inline] | |
2498 | fn cycle(self) -> Cycle<Self> where Self: Sized + Clone { | |
9fa01778 | 2499 | Cycle::new(self) |
a7813a04 XL |
2500 | } |
2501 | ||
2502 | /// Sums the elements of an iterator. | |
2503 | /// | |
2504 | /// Takes each element, adds them together, and returns the result. | |
2505 | /// | |
2506 | /// An empty iterator returns the zero value of the type. | |
2507 | /// | |
3157f602 XL |
2508 | /// # Panics |
2509 | /// | |
476ff2be | 2510 | /// When calling `sum()` and a primitive integer type is being returned, this |
9e0c209e SL |
2511 | /// method will panic if the computation overflows and debug assertions are |
2512 | /// enabled. | |
3157f602 | 2513 | /// |
a7813a04 XL |
2514 | /// # Examples |
2515 | /// | |
2516 | /// Basic usage: | |
2517 | /// | |
2518 | /// ``` | |
a7813a04 XL |
2519 | /// let a = [1, 2, 3]; |
2520 | /// let sum: i32 = a.iter().sum(); | |
2521 | /// | |
2522 | /// assert_eq!(sum, 6); | |
2523 | /// ``` | |
3157f602 XL |
2524 | #[stable(feature = "iter_arith", since = "1.11.0")] |
2525 | fn sum<S>(self) -> S | |
2526 | where Self: Sized, | |
2527 | S: Sum<Self::Item>, | |
a7813a04 | 2528 | { |
3157f602 | 2529 | Sum::sum(self) |
a7813a04 XL |
2530 | } |
2531 | ||
2532 | /// Iterates over the entire iterator, multiplying all the elements | |
2533 | /// | |
2534 | /// An empty iterator returns the one value of the type. | |
2535 | /// | |
3157f602 XL |
2536 | /// # Panics |
2537 | /// | |
476ff2be | 2538 | /// When calling `product()` and a primitive integer type is being returned, |
9e0c209e SL |
2539 | /// method will panic if the computation overflows and debug assertions are |
2540 | /// enabled. | |
3157f602 | 2541 | /// |
a7813a04 XL |
2542 | /// # Examples |
2543 | /// | |
2544 | /// ``` | |
a7813a04 | 2545 | /// fn factorial(n: u32) -> u32 { |
0731742a | 2546 | /// (1..=n).product() |
a7813a04 XL |
2547 | /// } |
2548 | /// assert_eq!(factorial(0), 1); | |
2549 | /// assert_eq!(factorial(1), 1); | |
2550 | /// assert_eq!(factorial(5), 120); | |
2551 | /// ``` | |
3157f602 XL |
2552 | #[stable(feature = "iter_arith", since = "1.11.0")] |
2553 | fn product<P>(self) -> P | |
2554 | where Self: Sized, | |
2555 | P: Product<Self::Item>, | |
a7813a04 | 2556 | { |
3157f602 | 2557 | Product::product(self) |
a7813a04 XL |
2558 | } |
2559 | ||
2560 | /// Lexicographically compares the elements of this `Iterator` with those | |
2561 | /// of another. | |
e1599b0c XL |
2562 | /// |
2563 | /// # Examples | |
2564 | /// | |
2565 | /// ``` | |
2566 | /// use std::cmp::Ordering; | |
2567 | /// | |
2568 | /// assert_eq!([1].iter().cmp([1].iter()), Ordering::Equal); | |
2569 | /// assert_eq!([1].iter().cmp([1, 2].iter()), Ordering::Less); | |
2570 | /// assert_eq!([1, 2].iter().cmp([1].iter()), Ordering::Greater); | |
2571 | /// ``` | |
a7813a04 | 2572 | #[stable(feature = "iter_order", since = "1.5.0")] |
e1599b0c XL |
2573 | fn cmp<I>(self, other: I) -> Ordering |
2574 | where | |
a7813a04 XL |
2575 | I: IntoIterator<Item = Self::Item>, |
2576 | Self::Item: Ord, | |
2577 | Self: Sized, | |
e1599b0c XL |
2578 | { |
2579 | self.cmp_by(other, |x, y| x.cmp(&y)) | |
2580 | } | |
2581 | ||
2582 | /// Lexicographically compares the elements of this `Iterator` with those | |
2583 | /// of another with respect to the specified comparison function. | |
2584 | /// | |
2585 | /// # Examples | |
2586 | /// | |
2587 | /// Basic usage: | |
2588 | /// | |
2589 | /// ``` | |
2590 | /// #![feature(iter_order_by)] | |
2591 | /// | |
2592 | /// use std::cmp::Ordering; | |
2593 | /// | |
2594 | /// let xs = [1, 2, 3, 4]; | |
2595 | /// let ys = [1, 4, 9, 16]; | |
2596 | /// | |
2597 | /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| x.cmp(&y)), Ordering::Less); | |
2598 | /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (x * x).cmp(&y)), Ordering::Equal); | |
2599 | /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (2 * x).cmp(&y)), Ordering::Greater); | |
2600 | /// ``` | |
e74abb32 | 2601 | #[unstable(feature = "iter_order_by", issue = "64295")] |
e1599b0c XL |
2602 | fn cmp_by<I, F>(mut self, other: I, mut cmp: F) -> Ordering |
2603 | where | |
2604 | Self: Sized, | |
2605 | I: IntoIterator, | |
2606 | F: FnMut(Self::Item, I::Item) -> Ordering, | |
a7813a04 XL |
2607 | { |
2608 | let mut other = other.into_iter(); | |
2609 | ||
2610 | loop { | |
abe05a73 XL |
2611 | let x = match self.next() { |
2612 | None => if other.next().is_none() { | |
2613 | return Ordering::Equal | |
2614 | } else { | |
2615 | return Ordering::Less | |
a7813a04 | 2616 | }, |
abe05a73 XL |
2617 | Some(val) => val, |
2618 | }; | |
2619 | ||
2620 | let y = match other.next() { | |
2621 | None => return Ordering::Greater, | |
2622 | Some(val) => val, | |
2623 | }; | |
2624 | ||
e1599b0c | 2625 | match cmp(x, y) { |
abe05a73 XL |
2626 | Ordering::Equal => (), |
2627 | non_eq => return non_eq, | |
a7813a04 XL |
2628 | } |
2629 | } | |
2630 | } | |
2631 | ||
2632 | /// Lexicographically compares the elements of this `Iterator` with those | |
2633 | /// of another. | |
e1599b0c XL |
2634 | /// |
2635 | /// # Examples | |
2636 | /// | |
2637 | /// ``` | |
2638 | /// use std::cmp::Ordering; | |
2639 | /// | |
2640 | /// assert_eq!([1.].iter().partial_cmp([1.].iter()), Some(Ordering::Equal)); | |
2641 | /// assert_eq!([1.].iter().partial_cmp([1., 2.].iter()), Some(Ordering::Less)); | |
2642 | /// assert_eq!([1., 2.].iter().partial_cmp([1.].iter()), Some(Ordering::Greater)); | |
2643 | /// | |
2644 | /// assert_eq!([std::f64::NAN].iter().partial_cmp([1.].iter()), None); | |
2645 | /// ``` | |
a7813a04 | 2646 | #[stable(feature = "iter_order", since = "1.5.0")] |
e1599b0c XL |
2647 | fn partial_cmp<I>(self, other: I) -> Option<Ordering> |
2648 | where | |
a7813a04 XL |
2649 | I: IntoIterator, |
2650 | Self::Item: PartialOrd<I::Item>, | |
2651 | Self: Sized, | |
e1599b0c XL |
2652 | { |
2653 | self.partial_cmp_by(other, |x, y| x.partial_cmp(&y)) | |
2654 | } | |
2655 | ||
2656 | /// Lexicographically compares the elements of this `Iterator` with those | |
2657 | /// of another with respect to the specified comparison function. | |
2658 | /// | |
2659 | /// # Examples | |
2660 | /// | |
2661 | /// Basic usage: | |
2662 | /// | |
2663 | /// ``` | |
2664 | /// #![feature(iter_order_by)] | |
2665 | /// | |
2666 | /// use std::cmp::Ordering; | |
2667 | /// | |
2668 | /// let xs = [1.0, 2.0, 3.0, 4.0]; | |
2669 | /// let ys = [1.0, 4.0, 9.0, 16.0]; | |
2670 | /// | |
2671 | /// assert_eq!( | |
2672 | /// xs.iter().partial_cmp_by(&ys, |&x, &y| x.partial_cmp(&y)), | |
2673 | /// Some(Ordering::Less) | |
2674 | /// ); | |
2675 | /// assert_eq!( | |
2676 | /// xs.iter().partial_cmp_by(&ys, |&x, &y| (x * x).partial_cmp(&y)), | |
2677 | /// Some(Ordering::Equal) | |
2678 | /// ); | |
2679 | /// assert_eq!( | |
2680 | /// xs.iter().partial_cmp_by(&ys, |&x, &y| (2.0 * x).partial_cmp(&y)), | |
2681 | /// Some(Ordering::Greater) | |
2682 | /// ); | |
2683 | /// ``` | |
e74abb32 | 2684 | #[unstable(feature = "iter_order_by", issue = "64295")] |
e1599b0c XL |
2685 | fn partial_cmp_by<I, F>(mut self, other: I, mut partial_cmp: F) -> Option<Ordering> |
2686 | where | |
2687 | Self: Sized, | |
2688 | I: IntoIterator, | |
2689 | F: FnMut(Self::Item, I::Item) -> Option<Ordering>, | |
a7813a04 XL |
2690 | { |
2691 | let mut other = other.into_iter(); | |
2692 | ||
2693 | loop { | |
abe05a73 XL |
2694 | let x = match self.next() { |
2695 | None => if other.next().is_none() { | |
2696 | return Some(Ordering::Equal) | |
2697 | } else { | |
2698 | return Some(Ordering::Less) | |
a7813a04 | 2699 | }, |
abe05a73 XL |
2700 | Some(val) => val, |
2701 | }; | |
2702 | ||
2703 | let y = match other.next() { | |
2704 | None => return Some(Ordering::Greater), | |
2705 | Some(val) => val, | |
2706 | }; | |
2707 | ||
e1599b0c | 2708 | match partial_cmp(x, y) { |
abe05a73 XL |
2709 | Some(Ordering::Equal) => (), |
2710 | non_eq => return non_eq, | |
a7813a04 XL |
2711 | } |
2712 | } | |
2713 | } | |
2714 | ||
2715 | /// Determines if the elements of this `Iterator` are equal to those of | |
2716 | /// another. | |
e1599b0c XL |
2717 | /// |
2718 | /// # Examples | |
2719 | /// | |
2720 | /// ``` | |
2721 | /// assert_eq!([1].iter().eq([1].iter()), true); | |
2722 | /// assert_eq!([1].iter().eq([1, 2].iter()), false); | |
2723 | /// ``` | |
a7813a04 | 2724 | #[stable(feature = "iter_order", since = "1.5.0")] |
e1599b0c XL |
2725 | fn eq<I>(self, other: I) -> bool |
2726 | where | |
a7813a04 XL |
2727 | I: IntoIterator, |
2728 | Self::Item: PartialEq<I::Item>, | |
2729 | Self: Sized, | |
e1599b0c XL |
2730 | { |
2731 | self.eq_by(other, |x, y| x == y) | |
2732 | } | |
2733 | ||
2734 | /// Determines if the elements of this `Iterator` are equal to those of | |
2735 | /// another with respect to the specified equality function. | |
2736 | /// | |
2737 | /// # Examples | |
2738 | /// | |
2739 | /// Basic usage: | |
2740 | /// | |
2741 | /// ``` | |
2742 | /// #![feature(iter_order_by)] | |
2743 | /// | |
2744 | /// let xs = [1, 2, 3, 4]; | |
2745 | /// let ys = [1, 4, 9, 16]; | |
2746 | /// | |
2747 | /// assert!(xs.iter().eq_by(&ys, |&x, &y| x * x == y)); | |
2748 | /// ``` | |
e74abb32 | 2749 | #[unstable(feature = "iter_order_by", issue = "64295")] |
e1599b0c XL |
2750 | fn eq_by<I, F>(mut self, other: I, mut eq: F) -> bool |
2751 | where | |
2752 | Self: Sized, | |
2753 | I: IntoIterator, | |
2754 | F: FnMut(Self::Item, I::Item) -> bool, | |
a7813a04 XL |
2755 | { |
2756 | let mut other = other.into_iter(); | |
2757 | ||
2758 | loop { | |
abe05a73 XL |
2759 | let x = match self.next() { |
2760 | None => return other.next().is_none(), | |
2761 | Some(val) => val, | |
2762 | }; | |
2763 | ||
2764 | let y = match other.next() { | |
2765 | None => return false, | |
2766 | Some(val) => val, | |
2767 | }; | |
2768 | ||
e1599b0c XL |
2769 | if !eq(x, y) { |
2770 | return false; | |
2771 | } | |
a7813a04 XL |
2772 | } |
2773 | } | |
2774 | ||
2775 | /// Determines if the elements of this `Iterator` are unequal to those of | |
2776 | /// another. | |
e1599b0c XL |
2777 | /// |
2778 | /// # Examples | |
2779 | /// | |
2780 | /// ``` | |
2781 | /// assert_eq!([1].iter().ne([1].iter()), false); | |
2782 | /// assert_eq!([1].iter().ne([1, 2].iter()), true); | |
2783 | /// ``` | |
a7813a04 | 2784 | #[stable(feature = "iter_order", since = "1.5.0")] |
532ac7d7 | 2785 | fn ne<I>(self, other: I) -> bool where |
a7813a04 XL |
2786 | I: IntoIterator, |
2787 | Self::Item: PartialEq<I::Item>, | |
2788 | Self: Sized, | |
2789 | { | |
532ac7d7 | 2790 | !self.eq(other) |
a7813a04 XL |
2791 | } |
2792 | ||
2793 | /// Determines if the elements of this `Iterator` are lexicographically | |
2794 | /// less than those of another. | |
e1599b0c XL |
2795 | /// |
2796 | /// # Examples | |
2797 | /// | |
2798 | /// ``` | |
2799 | /// assert_eq!([1].iter().lt([1].iter()), false); | |
2800 | /// assert_eq!([1].iter().lt([1, 2].iter()), true); | |
2801 | /// assert_eq!([1, 2].iter().lt([1].iter()), false); | |
2802 | /// ``` | |
a7813a04 | 2803 | #[stable(feature = "iter_order", since = "1.5.0")] |
532ac7d7 | 2804 | fn lt<I>(self, other: I) -> bool where |
a7813a04 XL |
2805 | I: IntoIterator, |
2806 | Self::Item: PartialOrd<I::Item>, | |
2807 | Self: Sized, | |
2808 | { | |
532ac7d7 | 2809 | self.partial_cmp(other) == Some(Ordering::Less) |
a7813a04 XL |
2810 | } |
2811 | ||
2812 | /// Determines if the elements of this `Iterator` are lexicographically | |
2813 | /// less or equal to those of another. | |
e1599b0c XL |
2814 | /// |
2815 | /// # Examples | |
2816 | /// | |
2817 | /// ``` | |
2818 | /// assert_eq!([1].iter().le([1].iter()), true); | |
2819 | /// assert_eq!([1].iter().le([1, 2].iter()), true); | |
2820 | /// assert_eq!([1, 2].iter().le([1].iter()), false); | |
2821 | /// ``` | |
a7813a04 | 2822 | #[stable(feature = "iter_order", since = "1.5.0")] |
532ac7d7 | 2823 | fn le<I>(self, other: I) -> bool where |
a7813a04 XL |
2824 | I: IntoIterator, |
2825 | Self::Item: PartialOrd<I::Item>, | |
2826 | Self: Sized, | |
2827 | { | |
532ac7d7 XL |
2828 | match self.partial_cmp(other) { |
2829 | Some(Ordering::Less) | Some(Ordering::Equal) => true, | |
2830 | _ => false, | |
a7813a04 XL |
2831 | } |
2832 | } | |
2833 | ||
2834 | /// Determines if the elements of this `Iterator` are lexicographically | |
2835 | /// greater than those of another. | |
e1599b0c XL |
2836 | /// |
2837 | /// # Examples | |
2838 | /// | |
2839 | /// ``` | |
2840 | /// assert_eq!([1].iter().gt([1].iter()), false); | |
2841 | /// assert_eq!([1].iter().gt([1, 2].iter()), false); | |
2842 | /// assert_eq!([1, 2].iter().gt([1].iter()), true); | |
2843 | /// ``` | |
a7813a04 | 2844 | #[stable(feature = "iter_order", since = "1.5.0")] |
532ac7d7 | 2845 | fn gt<I>(self, other: I) -> bool where |
a7813a04 XL |
2846 | I: IntoIterator, |
2847 | Self::Item: PartialOrd<I::Item>, | |
2848 | Self: Sized, | |
2849 | { | |
532ac7d7 | 2850 | self.partial_cmp(other) == Some(Ordering::Greater) |
a7813a04 XL |
2851 | } |
2852 | ||
2853 | /// Determines if the elements of this `Iterator` are lexicographically | |
2854 | /// greater than or equal to those of another. | |
e1599b0c XL |
2855 | /// |
2856 | /// # Examples | |
2857 | /// | |
2858 | /// ``` | |
2859 | /// assert_eq!([1].iter().ge([1].iter()), true); | |
2860 | /// assert_eq!([1].iter().ge([1, 2].iter()), false); | |
2861 | /// assert_eq!([1, 2].iter().ge([1].iter()), true); | |
2862 | /// ``` | |
a7813a04 | 2863 | #[stable(feature = "iter_order", since = "1.5.0")] |
532ac7d7 | 2864 | fn ge<I>(self, other: I) -> bool where |
a7813a04 XL |
2865 | I: IntoIterator, |
2866 | Self::Item: PartialOrd<I::Item>, | |
2867 | Self: Sized, | |
2868 | { | |
532ac7d7 XL |
2869 | match self.partial_cmp(other) { |
2870 | Some(Ordering::Greater) | Some(Ordering::Equal) => true, | |
2871 | _ => false, | |
a7813a04 XL |
2872 | } |
2873 | } | |
9fa01778 XL |
2874 | |
2875 | /// Checks if the elements of this iterator are sorted. | |
2876 | /// | |
2877 | /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the | |
2878 | /// iterator yields exactly zero or one element, `true` is returned. | |
2879 | /// | |
2880 | /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition | |
2881 | /// implies that this function returns `false` if any two consecutive items are not | |
2882 | /// comparable. | |
2883 | /// | |
2884 | /// # Examples | |
2885 | /// | |
2886 | /// ``` | |
2887 | /// #![feature(is_sorted)] | |
2888 | /// | |
2889 | /// assert!([1, 2, 2, 9].iter().is_sorted()); | |
2890 | /// assert!(![1, 3, 2, 4].iter().is_sorted()); | |
2891 | /// assert!([0].iter().is_sorted()); | |
2892 | /// assert!(std::iter::empty::<i32>().is_sorted()); | |
2893 | /// assert!(![0.0, 1.0, std::f32::NAN].iter().is_sorted()); | |
2894 | /// ``` | |
2895 | #[inline] | |
2896 | #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] | |
2897 | fn is_sorted(self) -> bool | |
2898 | where | |
2899 | Self: Sized, | |
2900 | Self::Item: PartialOrd, | |
2901 | { | |
e1599b0c | 2902 | self.is_sorted_by(PartialOrd::partial_cmp) |
9fa01778 XL |
2903 | } |
2904 | ||
2905 | /// Checks if the elements of this iterator are sorted using the given comparator function. | |
2906 | /// | |
2907 | /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare` | |
2908 | /// function to determine the ordering of two elements. Apart from that, it's equivalent to | |
2909 | /// [`is_sorted`]; see its documentation for more information. | |
2910 | /// | |
e1599b0c XL |
2911 | /// # Examples |
2912 | /// | |
2913 | /// ``` | |
2914 | /// #![feature(is_sorted)] | |
2915 | /// | |
2916 | /// assert!([1, 2, 2, 9].iter().is_sorted_by(|a, b| a.partial_cmp(b))); | |
2917 | /// assert!(![1, 3, 2, 4].iter().is_sorted_by(|a, b| a.partial_cmp(b))); | |
2918 | /// assert!([0].iter().is_sorted_by(|a, b| a.partial_cmp(b))); | |
2919 | /// assert!(std::iter::empty::<i32>().is_sorted_by(|a, b| a.partial_cmp(b))); | |
2920 | /// assert!(![0.0, 1.0, std::f32::NAN].iter().is_sorted_by(|a, b| a.partial_cmp(b))); | |
2921 | /// ``` | |
2922 | /// | |
9fa01778 XL |
2923 | /// [`is_sorted`]: trait.Iterator.html#method.is_sorted |
2924 | #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] | |
2925 | fn is_sorted_by<F>(mut self, mut compare: F) -> bool | |
2926 | where | |
2927 | Self: Sized, | |
2928 | F: FnMut(&Self::Item, &Self::Item) -> Option<Ordering> | |
2929 | { | |
2930 | let mut last = match self.next() { | |
2931 | Some(e) => e, | |
2932 | None => return true, | |
2933 | }; | |
2934 | ||
2935 | while let Some(curr) = self.next() { | |
e1599b0c | 2936 | if let Some(Ordering::Greater) | None = compare(&last, &curr) { |
9fa01778 XL |
2937 | return false; |
2938 | } | |
2939 | last = curr; | |
2940 | } | |
2941 | ||
2942 | true | |
2943 | } | |
2944 | ||
2945 | /// Checks if the elements of this iterator are sorted using the given key extraction | |
2946 | /// function. | |
2947 | /// | |
2948 | /// Instead of comparing the iterator's elements directly, this function compares the keys of | |
2949 | /// the elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see | |
2950 | /// its documentation for more information. | |
2951 | /// | |
2952 | /// [`is_sorted`]: trait.Iterator.html#method.is_sorted | |
2953 | /// | |
2954 | /// # Examples | |
2955 | /// | |
2956 | /// ``` | |
2957 | /// #![feature(is_sorted)] | |
2958 | /// | |
2959 | /// assert!(["c", "bb", "aaa"].iter().is_sorted_by_key(|s| s.len())); | |
2960 | /// assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs())); | |
2961 | /// ``` | |
2962 | #[inline] | |
2963 | #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] | |
416331ca | 2964 | fn is_sorted_by_key<F, K>(self, f: F) -> bool |
9fa01778 XL |
2965 | where |
2966 | Self: Sized, | |
416331ca | 2967 | F: FnMut(Self::Item) -> K, |
9fa01778 XL |
2968 | K: PartialOrd |
2969 | { | |
416331ca | 2970 | self.map(f).is_sorted() |
9fa01778 | 2971 | } |
a7813a04 XL |
2972 | } |
2973 | ||
e1599b0c | 2974 | /// Fold an iterator without having to provide an initial value. |
a7813a04 | 2975 | #[inline] |
e1599b0c | 2976 | fn fold1<I, F>(mut it: I, f: F) -> Option<I::Item> |
532ac7d7 XL |
2977 | where |
2978 | I: Iterator, | |
e1599b0c | 2979 | F: FnMut(I::Item, I::Item) -> I::Item, |
a7813a04 XL |
2980 | { |
2981 | // start with the first element as our selection. This avoids | |
2982 | // having to use `Option`s inside the loop, translating to a | |
2983 | // sizeable performance gain (6x in one case). | |
e1599b0c XL |
2984 | let first = it.next()?; |
2985 | Some(it.fold(first, f)) | |
a7813a04 XL |
2986 | } |
2987 | ||
2988 | #[stable(feature = "rust1", since = "1.0.0")] | |
0bf4aa26 | 2989 | impl<I: Iterator + ?Sized> Iterator for &mut I { |
a7813a04 XL |
2990 | type Item = I::Item; |
2991 | fn next(&mut self) -> Option<I::Item> { (**self).next() } | |
2992 | fn size_hint(&self) -> (usize, Option<usize>) { (**self).size_hint() } | |
476ff2be SL |
2993 | fn nth(&mut self, n: usize) -> Option<Self::Item> { |
2994 | (**self).nth(n) | |
2995 | } | |
a7813a04 | 2996 | } |