1 // Copyright 2013-2016 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
14 use super::{AlwaysOk, LoopState}
;
15 use super::{Chain, Cycle, Cloned, Enumerate, Filter, FilterMap, Fuse}
;
16 use super::{Flatten, FlatMap, flatten_compat}
;
17 use super::{Inspect, Map, Peekable, Scan, Skip, SkipWhile, StepBy, Take, TakeWhile, Rev}
;
18 use super::{Zip, Sum, Product}
;
19 use super::{ChainState, FromIterator, ZipImpl}
;
21 fn _assert_is_object_safe(_
: &Iterator
<Item
=()>) {}
23 /// An interface for dealing with iterators.
25 /// This is the main iterator trait. For more about the concept of iterators
26 /// generally, please see the [module-level documentation]. In particular, you
27 /// may want to know how to [implement `Iterator`][impl].
29 /// [module-level documentation]: index.html
30 /// [impl]: index.html#implementing-iterator
31 #[stable(feature = "rust1", since = "1.0.0")]
32 #[rustc_on_unimplemented(
35 label
="`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`"
37 label
="`{Self}` is not an iterator; maybe try calling `.iter()` or a similar method"
41 /// The type of the elements being iterated over.
42 #[stable(feature = "rust1", since = "1.0.0")]
45 /// Advances the iterator and returns the next value.
47 /// Returns [`None`] when iteration is finished. Individual iterator
48 /// implementations may choose to resume iteration, and so calling `next()`
49 /// again may or may not eventually start returning [`Some(Item)`] again at some
52 /// [`None`]: ../../std/option/enum.Option.html#variant.None
53 /// [`Some(Item)`]: ../../std/option/enum.Option.html#variant.Some
60 /// let a = [1, 2, 3];
62 /// let mut iter = a.iter();
64 /// // A call to next() returns the next value...
65 /// assert_eq!(Some(&1), iter.next());
66 /// assert_eq!(Some(&2), iter.next());
67 /// assert_eq!(Some(&3), iter.next());
69 /// // ... and then None once it's over.
70 /// assert_eq!(None, iter.next());
72 /// // More calls may or may not return None. Here, they always will.
73 /// assert_eq!(None, iter.next());
74 /// assert_eq!(None, iter.next());
76 #[stable(feature = "rust1", since = "1.0.0")]
77 fn next(&mut self) -> Option
<Self::Item
>;
79 /// Returns the bounds on the remaining length of the iterator.
81 /// Specifically, `size_hint()` returns a tuple where the first element
82 /// is the lower bound, and the second element is the upper bound.
84 /// The second half of the tuple that is returned is an [`Option`]`<`[`usize`]`>`.
85 /// A [`None`] here means that either there is no known upper bound, or the
86 /// upper bound is larger than [`usize`].
88 /// # Implementation notes
90 /// It is not enforced that an iterator implementation yields the declared
91 /// number of elements. A buggy iterator may yield less than the lower bound
92 /// or more than the upper bound of elements.
94 /// `size_hint()` is primarily intended to be used for optimizations such as
95 /// reserving space for the elements of the iterator, but must not be
96 /// trusted to e.g. omit bounds checks in unsafe code. An incorrect
97 /// implementation of `size_hint()` should not lead to memory safety
100 /// That said, the implementation should provide a correct estimation,
101 /// because otherwise it would be a violation of the trait's protocol.
103 /// The default implementation returns `(0, None)` which is correct for any
106 /// [`usize`]: ../../std/primitive.usize.html
107 /// [`Option`]: ../../std/option/enum.Option.html
108 /// [`None`]: ../../std/option/enum.Option.html#variant.None
115 /// let a = [1, 2, 3];
116 /// let iter = a.iter();
118 /// assert_eq!((3, Some(3)), iter.size_hint());
121 /// A more complex example:
124 /// // The even numbers from zero to ten.
125 /// let iter = (0..10).filter(|x| x % 2 == 0);
127 /// // We might iterate from zero to ten times. Knowing that it's five
128 /// // exactly wouldn't be possible without executing filter().
129 /// assert_eq!((0, Some(10)), iter.size_hint());
131 /// // Let's add five more numbers with chain()
132 /// let iter = (0..10).filter(|x| x % 2 == 0).chain(15..20);
134 /// // now both bounds are increased by five
135 /// assert_eq!((5, Some(15)), iter.size_hint());
138 /// Returning `None` for an upper bound:
141 /// // an infinite iterator has no upper bound
142 /// // and the maximum possible lower bound
145 /// assert_eq!((usize::max_value(), None), iter.size_hint());
148 #[stable(feature = "rust1", since = "1.0.0")]
149 fn size_hint(&self) -> (usize, Option
<usize>) { (0, None) }
151 /// Consumes the iterator, counting the number of iterations and returning it.
153 /// This method will evaluate the iterator until its [`next`] returns
154 /// [`None`]. Once [`None`] is encountered, `count()` returns the number of
155 /// times it called [`next`].
157 /// [`next`]: #tymethod.next
158 /// [`None`]: ../../std/option/enum.Option.html#variant.None
160 /// # Overflow Behavior
162 /// The method does no guarding against overflows, so counting elements of
163 /// an iterator with more than [`usize::MAX`] elements either produces the
164 /// wrong result or panics. If debug assertions are enabled, a panic is
169 /// This function might panic if the iterator has more than [`usize::MAX`]
172 /// [`usize::MAX`]: ../../std/usize/constant.MAX.html
179 /// let a = [1, 2, 3];
180 /// assert_eq!(a.iter().count(), 3);
182 /// let a = [1, 2, 3, 4, 5];
183 /// assert_eq!(a.iter().count(), 5);
186 #[rustc_inherit_overflow_checks]
187 #[stable(feature = "rust1", since = "1.0.0")]
188 fn count(self) -> usize where Self: Sized
{
190 self.fold(0, |cnt
, _
| cnt
+ 1)
193 /// Consumes the iterator, returning the last element.
195 /// This method will evaluate the iterator until it returns [`None`]. While
196 /// doing so, it keeps track of the current element. After [`None`] is
197 /// returned, `last()` will then return the last element it saw.
199 /// [`None`]: ../../std/option/enum.Option.html#variant.None
206 /// let a = [1, 2, 3];
207 /// assert_eq!(a.iter().last(), Some(&3));
209 /// let a = [1, 2, 3, 4, 5];
210 /// assert_eq!(a.iter().last(), Some(&5));
213 #[stable(feature = "rust1", since = "1.0.0")]
214 fn last(self) -> Option
<Self::Item
> where Self: Sized
{
216 for x
in self { last = Some(x); }
220 /// Returns the `n`th element of the iterator.
222 /// Like most indexing operations, the count starts from zero, so `nth(0)`
223 /// returns the first value, `nth(1)` the second, and so on.
225 /// Note that all preceding elements, as well as the returned element, will be
226 /// consumed from the iterator. That means that the preceding elements will be
227 /// discarded, and also that calling `nth(0)` multiple times on the same iterator
228 /// will return different elements.
230 /// `nth()` will return [`None`] if `n` is greater than or equal to the length of the
233 /// [`None`]: ../../std/option/enum.Option.html#variant.None
240 /// let a = [1, 2, 3];
241 /// assert_eq!(a.iter().nth(1), Some(&2));
244 /// Calling `nth()` multiple times doesn't rewind the iterator:
247 /// let a = [1, 2, 3];
249 /// let mut iter = a.iter();
251 /// assert_eq!(iter.nth(1), Some(&2));
252 /// assert_eq!(iter.nth(1), None);
255 /// Returning `None` if there are less than `n + 1` elements:
258 /// let a = [1, 2, 3];
259 /// assert_eq!(a.iter().nth(10), None);
262 #[stable(feature = "rust1", since = "1.0.0")]
263 fn nth(&mut self, mut n
: usize) -> Option
<Self::Item
> {
265 if n
== 0 { return Some(x) }
271 /// Creates an iterator starting at the same point, but stepping by
272 /// the given amount at each iteration.
274 /// Note that it will always return the first element of the iterator,
275 /// regardless of the step given.
279 /// The method will panic if the given step is `0`.
286 /// #![feature(iterator_step_by)]
287 /// let a = [0, 1, 2, 3, 4, 5];
288 /// let mut iter = a.into_iter().step_by(2);
290 /// assert_eq!(iter.next(), Some(&0));
291 /// assert_eq!(iter.next(), Some(&2));
292 /// assert_eq!(iter.next(), Some(&4));
293 /// assert_eq!(iter.next(), None);
296 #[unstable(feature = "iterator_step_by",
297 reason
= "unstable replacement of Range::step_by",
299 fn step_by(self, step
: usize) -> StepBy
<Self> where Self: Sized
{
301 StepBy{iter: self, step: step - 1, first_take: true}
304 /// Takes two iterators and creates a new iterator over both in sequence.
306 /// `chain()` will return a new iterator which will first iterate over
307 /// values from the first iterator and then over values from the second
310 /// In other words, it links two iterators together, in a chain. 🔗
317 /// let a1 = [1, 2, 3];
318 /// let a2 = [4, 5, 6];
320 /// let mut iter = a1.iter().chain(a2.iter());
322 /// assert_eq!(iter.next(), Some(&1));
323 /// assert_eq!(iter.next(), Some(&2));
324 /// assert_eq!(iter.next(), Some(&3));
325 /// assert_eq!(iter.next(), Some(&4));
326 /// assert_eq!(iter.next(), Some(&5));
327 /// assert_eq!(iter.next(), Some(&6));
328 /// assert_eq!(iter.next(), None);
331 /// Since the argument to `chain()` uses [`IntoIterator`], we can pass
332 /// anything that can be converted into an [`Iterator`], not just an
333 /// [`Iterator`] itself. For example, slices (`&[T]`) implement
334 /// [`IntoIterator`], and so can be passed to `chain()` directly:
336 /// [`IntoIterator`]: trait.IntoIterator.html
337 /// [`Iterator`]: trait.Iterator.html
340 /// let s1 = &[1, 2, 3];
341 /// let s2 = &[4, 5, 6];
343 /// let mut iter = s1.iter().chain(s2);
345 /// assert_eq!(iter.next(), Some(&1));
346 /// assert_eq!(iter.next(), Some(&2));
347 /// assert_eq!(iter.next(), Some(&3));
348 /// assert_eq!(iter.next(), Some(&4));
349 /// assert_eq!(iter.next(), Some(&5));
350 /// assert_eq!(iter.next(), Some(&6));
351 /// assert_eq!(iter.next(), None);
354 #[stable(feature = "rust1", since = "1.0.0")]
355 fn chain
<U
>(self, other
: U
) -> Chain
<Self, U
::IntoIter
> where
356 Self: Sized
, U
: IntoIterator
<Item
=Self::Item
>,
358 Chain{a: self, b: other.into_iter(), state: ChainState::Both}
361 /// 'Zips up' two iterators into a single iterator of pairs.
363 /// `zip()` returns a new iterator that will iterate over two other
364 /// iterators, returning a tuple where the first element comes from the
365 /// first iterator, and the second element comes from the second iterator.
367 /// In other words, it zips two iterators together, into a single one.
369 /// When either iterator returns [`None`], all further calls to [`next`]
370 /// will return [`None`].
377 /// let a1 = [1, 2, 3];
378 /// let a2 = [4, 5, 6];
380 /// let mut iter = a1.iter().zip(a2.iter());
382 /// assert_eq!(iter.next(), Some((&1, &4)));
383 /// assert_eq!(iter.next(), Some((&2, &5)));
384 /// assert_eq!(iter.next(), Some((&3, &6)));
385 /// assert_eq!(iter.next(), None);
388 /// Since the argument to `zip()` uses [`IntoIterator`], we can pass
389 /// anything that can be converted into an [`Iterator`], not just an
390 /// [`Iterator`] itself. For example, slices (`&[T]`) implement
391 /// [`IntoIterator`], and so can be passed to `zip()` directly:
393 /// [`IntoIterator`]: trait.IntoIterator.html
394 /// [`Iterator`]: trait.Iterator.html
397 /// let s1 = &[1, 2, 3];
398 /// let s2 = &[4, 5, 6];
400 /// let mut iter = s1.iter().zip(s2);
402 /// assert_eq!(iter.next(), Some((&1, &4)));
403 /// assert_eq!(iter.next(), Some((&2, &5)));
404 /// assert_eq!(iter.next(), Some((&3, &6)));
405 /// assert_eq!(iter.next(), None);
408 /// `zip()` is often used to zip an infinite iterator to a finite one.
409 /// This works because the finite iterator will eventually return [`None`],
410 /// ending the zipper. Zipping with `(0..)` can look a lot like [`enumerate`]:
413 /// let enumerate: Vec<_> = "foo".chars().enumerate().collect();
415 /// let zipper: Vec<_> = (0..).zip("foo".chars()).collect();
417 /// assert_eq!((0, 'f'), enumerate[0]);
418 /// assert_eq!((0, 'f'), zipper[0]);
420 /// assert_eq!((1, 'o'), enumerate[1]);
421 /// assert_eq!((1, 'o'), zipper[1]);
423 /// assert_eq!((2, 'o'), enumerate[2]);
424 /// assert_eq!((2, 'o'), zipper[2]);
427 /// [`enumerate`]: trait.Iterator.html#method.enumerate
428 /// [`next`]: ../../std/iter/trait.Iterator.html#tymethod.next
429 /// [`None`]: ../../std/option/enum.Option.html#variant.None
431 #[stable(feature = "rust1", since = "1.0.0")]
432 fn zip
<U
>(self, other
: U
) -> Zip
<Self, U
::IntoIter
> where
433 Self: Sized
, U
: IntoIterator
435 Zip
::new(self, other
.into_iter())
438 /// Takes a closure and creates an iterator which calls that closure on each
441 /// `map()` transforms one iterator into another, by means of its argument:
442 /// something that implements `FnMut`. It produces a new iterator which
443 /// calls this closure on each element of the original iterator.
445 /// If you are good at thinking in types, you can think of `map()` like this:
446 /// If you have an iterator that gives you elements of some type `A`, and
447 /// you want an iterator of some other type `B`, you can use `map()`,
448 /// passing a closure that takes an `A` and returns a `B`.
450 /// `map()` is conceptually similar to a [`for`] loop. However, as `map()` is
451 /// lazy, it is best used when you're already working with other iterators.
452 /// If you're doing some sort of looping for a side effect, it's considered
453 /// more idiomatic to use [`for`] than `map()`.
455 /// [`for`]: ../../book/first-edition/loops.html#for
462 /// let a = [1, 2, 3];
464 /// let mut iter = a.into_iter().map(|x| 2 * x);
466 /// assert_eq!(iter.next(), Some(2));
467 /// assert_eq!(iter.next(), Some(4));
468 /// assert_eq!(iter.next(), Some(6));
469 /// assert_eq!(iter.next(), None);
472 /// If you're doing some sort of side effect, prefer [`for`] to `map()`:
475 /// # #![allow(unused_must_use)]
476 /// // don't do this:
477 /// (0..5).map(|x| println!("{}", x));
479 /// // it won't even execute, as it is lazy. Rust will warn you about this.
481 /// // Instead, use for:
483 /// println!("{}", x);
487 #[stable(feature = "rust1", since = "1.0.0")]
488 fn map
<B
, F
>(self, f
: F
) -> Map
<Self, F
> where
489 Self: Sized
, F
: FnMut(Self::Item
) -> B
,
491 Map{iter: self, f: f}
494 /// Calls a closure on each element of an iterator.
496 /// This is equivalent to using a [`for`] loop on the iterator, although
497 /// `break` and `continue` are not possible from a closure. It's generally
498 /// more idiomatic to use a `for` loop, but `for_each` may be more legible
499 /// when processing items at the end of longer iterator chains. In some
500 /// cases `for_each` may also be faster than a loop, because it will use
501 /// internal iteration on adaptors like `Chain`.
503 /// [`for`]: ../../book/first-edition/loops.html#for
510 /// use std::sync::mpsc::channel;
512 /// let (tx, rx) = channel();
513 /// (0..5).map(|x| x * 2 + 1)
514 /// .for_each(move |x| tx.send(x).unwrap());
516 /// let v: Vec<_> = rx.iter().collect();
517 /// assert_eq!(v, vec![1, 3, 5, 7, 9]);
520 /// For such a small example, a `for` loop may be cleaner, but `for_each`
521 /// might be preferable to keep a functional style with longer iterators:
524 /// (0..5).flat_map(|x| x * 100 .. x * 110)
526 /// .filter(|&(i, x)| (i + x) % 3 == 0)
527 /// .for_each(|(i, x)| println!("{}:{}", i, x));
530 #[stable(feature = "iterator_for_each", since = "1.21.0")]
531 fn for_each
<F
>(self, mut f
: F
) where
532 Self: Sized
, F
: FnMut(Self::Item
),
534 self.fold((), move |(), item
| f(item
));
537 /// Creates an iterator which uses a closure to determine if an element
538 /// should be yielded.
540 /// The closure must return `true` or `false`. `filter()` creates an
541 /// iterator which calls this closure on each element. If the closure
542 /// returns `true`, then the element is returned. If the closure returns
543 /// `false`, it will try again, and call the closure on the next element,
544 /// seeing if it passes the test.
551 /// let a = [0i32, 1, 2];
553 /// let mut iter = a.into_iter().filter(|x| x.is_positive());
555 /// assert_eq!(iter.next(), Some(&1));
556 /// assert_eq!(iter.next(), Some(&2));
557 /// assert_eq!(iter.next(), None);
560 /// Because the closure passed to `filter()` takes a reference, and many
561 /// iterators iterate over references, this leads to a possibly confusing
562 /// situation, where the type of the closure is a double reference:
565 /// let a = [0, 1, 2];
567 /// let mut iter = a.into_iter().filter(|x| **x > 1); // need two *s!
569 /// assert_eq!(iter.next(), Some(&2));
570 /// assert_eq!(iter.next(), None);
573 /// It's common to instead use destructuring on the argument to strip away
577 /// let a = [0, 1, 2];
579 /// let mut iter = a.into_iter().filter(|&x| *x > 1); // both & and *
581 /// assert_eq!(iter.next(), Some(&2));
582 /// assert_eq!(iter.next(), None);
588 /// let a = [0, 1, 2];
590 /// let mut iter = a.into_iter().filter(|&&x| x > 1); // two &s
592 /// assert_eq!(iter.next(), Some(&2));
593 /// assert_eq!(iter.next(), None);
598 #[stable(feature = "rust1", since = "1.0.0")]
599 fn filter
<P
>(self, predicate
: P
) -> Filter
<Self, P
> where
600 Self: Sized
, P
: FnMut(&Self::Item
) -> bool
,
602 Filter{iter: self, predicate: predicate}
605 /// Creates an iterator that both filters and maps.
607 /// The closure must return an [`Option<T>`]. `filter_map` creates an
608 /// iterator which calls this closure on each element. If the closure
609 /// returns [`Some(element)`][`Some`], then that element is returned. If the
610 /// closure returns [`None`], it will try again, and call the closure on the
611 /// next element, seeing if it will return [`Some`].
613 /// Why `filter_map` and not just [`filter`] and [`map`]? The key is in this
616 /// [`filter`]: #method.filter
617 /// [`map`]: #method.map
619 /// > If the closure returns [`Some(element)`][`Some`], then that element is returned.
621 /// In other words, it removes the [`Option<T>`] layer automatically. If your
622 /// mapping is already returning an [`Option<T>`] and you want to skip over
623 /// [`None`]s, then `filter_map` is much, much nicer to use.
630 /// let a = ["1", "lol", "3", "NaN", "5"];
632 /// let mut iter = a.iter().filter_map(|s| s.parse().ok());
634 /// assert_eq!(iter.next(), Some(1));
635 /// assert_eq!(iter.next(), Some(3));
636 /// assert_eq!(iter.next(), Some(5));
637 /// assert_eq!(iter.next(), None);
640 /// Here's the same example, but with [`filter`] and [`map`]:
643 /// let a = ["1", "lol", "3", "NaN", "5"];
644 /// let mut iter = a.iter().map(|s| s.parse()).filter(|s| s.is_ok()).map(|s| s.unwrap());
645 /// assert_eq!(iter.next(), Some(1));
646 /// assert_eq!(iter.next(), Some(3));
647 /// assert_eq!(iter.next(), Some(5));
648 /// assert_eq!(iter.next(), None);
651 /// [`Option<T>`]: ../../std/option/enum.Option.html
652 /// [`Some`]: ../../std/option/enum.Option.html#variant.Some
653 /// [`None`]: ../../std/option/enum.Option.html#variant.None
655 #[stable(feature = "rust1", since = "1.0.0")]
656 fn filter_map
<B
, F
>(self, f
: F
) -> FilterMap
<Self, F
> where
657 Self: Sized
, F
: FnMut(Self::Item
) -> Option
<B
>,
659 FilterMap { iter: self, f: f }
662 /// Creates an iterator which gives the current iteration count as well as
665 /// The iterator returned yields pairs `(i, val)`, where `i` is the
666 /// current index of iteration and `val` is the value returned by the
669 /// `enumerate()` keeps its count as a [`usize`]. If you want to count by a
670 /// different sized integer, the [`zip`] function provides similar
673 /// # Overflow Behavior
675 /// The method does no guarding against overflows, so enumerating more than
676 /// [`usize::MAX`] elements either produces the wrong result or panics. If
677 /// debug assertions are enabled, a panic is guaranteed.
681 /// The returned iterator might panic if the to-be-returned index would
682 /// overflow a [`usize`].
684 /// [`usize::MAX`]: ../../std/usize/constant.MAX.html
685 /// [`usize`]: ../../std/primitive.usize.html
686 /// [`zip`]: #method.zip
691 /// let a = ['a', 'b', 'c'];
693 /// let mut iter = a.iter().enumerate();
695 /// assert_eq!(iter.next(), Some((0, &'a')));
696 /// assert_eq!(iter.next(), Some((1, &'b')));
697 /// assert_eq!(iter.next(), Some((2, &'c')));
698 /// assert_eq!(iter.next(), None);
701 #[stable(feature = "rust1", since = "1.0.0")]
702 fn enumerate(self) -> Enumerate
<Self> where Self: Sized
{
703 Enumerate { iter: self, count: 0 }
706 /// Creates an iterator which can use `peek` to look at the next element of
707 /// the iterator without consuming it.
709 /// Adds a [`peek`] method to an iterator. See its documentation for
710 /// more information.
712 /// Note that the underlying iterator is still advanced when [`peek`] is
713 /// called for the first time: In order to retrieve the next element,
714 /// [`next`] is called on the underlying iterator, hence any side effects (i.e.
715 /// anything other than fetching the next value) of the [`next`] method
718 /// [`peek`]: struct.Peekable.html#method.peek
719 /// [`next`]: ../../std/iter/trait.Iterator.html#tymethod.next
726 /// let xs = [1, 2, 3];
728 /// let mut iter = xs.iter().peekable();
730 /// // peek() lets us see into the future
731 /// assert_eq!(iter.peek(), Some(&&1));
732 /// assert_eq!(iter.next(), Some(&1));
734 /// assert_eq!(iter.next(), Some(&2));
736 /// // we can peek() multiple times, the iterator won't advance
737 /// assert_eq!(iter.peek(), Some(&&3));
738 /// assert_eq!(iter.peek(), Some(&&3));
740 /// assert_eq!(iter.next(), Some(&3));
742 /// // after the iterator is finished, so is peek()
743 /// assert_eq!(iter.peek(), None);
744 /// assert_eq!(iter.next(), None);
747 #[stable(feature = "rust1", since = "1.0.0")]
748 fn peekable(self) -> Peekable
<Self> where Self: Sized
{
749 Peekable{iter: self, peeked: None}
752 /// Creates an iterator that [`skip`]s elements based on a predicate.
754 /// [`skip`]: #method.skip
756 /// `skip_while()` takes a closure as an argument. It will call this
757 /// closure on each element of the iterator, and ignore elements
758 /// until it returns `false`.
760 /// After `false` is returned, `skip_while()`'s job is over, and the
761 /// rest of the elements are yielded.
768 /// let a = [-1i32, 0, 1];
770 /// let mut iter = a.into_iter().skip_while(|x| x.is_negative());
772 /// assert_eq!(iter.next(), Some(&0));
773 /// assert_eq!(iter.next(), Some(&1));
774 /// assert_eq!(iter.next(), None);
777 /// Because the closure passed to `skip_while()` takes a reference, and many
778 /// iterators iterate over references, this leads to a possibly confusing
779 /// situation, where the type of the closure is a double reference:
782 /// let a = [-1, 0, 1];
784 /// let mut iter = a.into_iter().skip_while(|x| **x < 0); // need two *s!
786 /// assert_eq!(iter.next(), Some(&0));
787 /// assert_eq!(iter.next(), Some(&1));
788 /// assert_eq!(iter.next(), None);
791 /// Stopping after an initial `false`:
794 /// let a = [-1, 0, 1, -2];
796 /// let mut iter = a.into_iter().skip_while(|x| **x < 0);
798 /// assert_eq!(iter.next(), Some(&0));
799 /// assert_eq!(iter.next(), Some(&1));
801 /// // while this would have been false, since we already got a false,
802 /// // skip_while() isn't used any more
803 /// assert_eq!(iter.next(), Some(&-2));
805 /// assert_eq!(iter.next(), None);
808 #[stable(feature = "rust1", since = "1.0.0")]
809 fn skip_while
<P
>(self, predicate
: P
) -> SkipWhile
<Self, P
> where
810 Self: Sized
, P
: FnMut(&Self::Item
) -> bool
,
812 SkipWhile{iter: self, flag: false, predicate: predicate}
815 /// Creates an iterator that yields elements based on a predicate.
817 /// `take_while()` takes a closure as an argument. It will call this
818 /// closure on each element of the iterator, and yield elements
819 /// while it returns `true`.
821 /// After `false` is returned, `take_while()`'s job is over, and the
822 /// rest of the elements are ignored.
829 /// let a = [-1i32, 0, 1];
831 /// let mut iter = a.into_iter().take_while(|x| x.is_negative());
833 /// assert_eq!(iter.next(), Some(&-1));
834 /// assert_eq!(iter.next(), None);
837 /// Because the closure passed to `take_while()` takes a reference, and many
838 /// iterators iterate over references, this leads to a possibly confusing
839 /// situation, where the type of the closure is a double reference:
842 /// let a = [-1, 0, 1];
844 /// let mut iter = a.into_iter().take_while(|x| **x < 0); // need two *s!
846 /// assert_eq!(iter.next(), Some(&-1));
847 /// assert_eq!(iter.next(), None);
850 /// Stopping after an initial `false`:
853 /// let a = [-1, 0, 1, -2];
855 /// let mut iter = a.into_iter().take_while(|x| **x < 0);
857 /// assert_eq!(iter.next(), Some(&-1));
859 /// // We have more elements that are less than zero, but since we already
860 /// // got a false, take_while() isn't used any more
861 /// assert_eq!(iter.next(), None);
864 /// Because `take_while()` needs to look at the value in order to see if it
865 /// should be included or not, consuming iterators will see that it is
869 /// let a = [1, 2, 3, 4];
870 /// let mut iter = a.into_iter();
872 /// let result: Vec<i32> = iter.by_ref()
873 /// .take_while(|n| **n != 3)
877 /// assert_eq!(result, &[1, 2]);
879 /// let result: Vec<i32> = iter.cloned().collect();
881 /// assert_eq!(result, &[4]);
884 /// The `3` is no longer there, because it was consumed in order to see if
885 /// the iteration should stop, but wasn't placed back into the iterator or
886 /// some similar thing.
888 #[stable(feature = "rust1", since = "1.0.0")]
889 fn take_while
<P
>(self, predicate
: P
) -> TakeWhile
<Self, P
> where
890 Self: Sized
, P
: FnMut(&Self::Item
) -> bool
,
892 TakeWhile{iter: self, flag: false, predicate: predicate}
895 /// Creates an iterator that skips the first `n` elements.
897 /// After they have been consumed, the rest of the elements are yielded.
904 /// let a = [1, 2, 3];
906 /// let mut iter = a.iter().skip(2);
908 /// assert_eq!(iter.next(), Some(&3));
909 /// assert_eq!(iter.next(), None);
912 #[stable(feature = "rust1", since = "1.0.0")]
913 fn skip(self, n
: usize) -> Skip
<Self> where Self: Sized
{
914 Skip{iter: self, n: n}
917 /// Creates an iterator that yields its first `n` elements.
924 /// let a = [1, 2, 3];
926 /// let mut iter = a.iter().take(2);
928 /// assert_eq!(iter.next(), Some(&1));
929 /// assert_eq!(iter.next(), Some(&2));
930 /// assert_eq!(iter.next(), None);
933 /// `take()` is often used with an infinite iterator, to make it finite:
936 /// let mut iter = (0..).take(3);
938 /// assert_eq!(iter.next(), Some(0));
939 /// assert_eq!(iter.next(), Some(1));
940 /// assert_eq!(iter.next(), Some(2));
941 /// assert_eq!(iter.next(), None);
944 #[stable(feature = "rust1", since = "1.0.0")]
945 fn take(self, n
: usize) -> Take
<Self> where Self: Sized
, {
946 Take{iter: self, n: n}
949 /// An iterator adaptor similar to [`fold`] that holds internal state and
950 /// produces a new iterator.
952 /// [`fold`]: #method.fold
954 /// `scan()` takes two arguments: an initial value which seeds the internal
955 /// state, and a closure with two arguments, the first being a mutable
956 /// reference to the internal state and the second an iterator element.
957 /// The closure can assign to the internal state to share state between
960 /// On iteration, the closure will be applied to each element of the
961 /// iterator and the return value from the closure, an [`Option`], is
962 /// yielded by the iterator.
964 /// [`Option`]: ../../std/option/enum.Option.html
971 /// let a = [1, 2, 3];
973 /// let mut iter = a.iter().scan(1, |state, &x| {
974 /// // each iteration, we'll multiply the state by the element
975 /// *state = *state * x;
977 /// // then, we'll yield the negation of the state
981 /// assert_eq!(iter.next(), Some(-1));
982 /// assert_eq!(iter.next(), Some(-2));
983 /// assert_eq!(iter.next(), Some(-6));
984 /// assert_eq!(iter.next(), None);
987 #[stable(feature = "rust1", since = "1.0.0")]
988 fn scan
<St
, B
, F
>(self, initial_state
: St
, f
: F
) -> Scan
<Self, St
, F
>
989 where Self: Sized
, F
: FnMut(&mut St
, Self::Item
) -> Option
<B
>,
991 Scan{iter: self, f: f, state: initial_state}
994 /// Creates an iterator that works like map, but flattens nested structure.
996 /// The [`map`] adapter is very useful, but only when the closure
997 /// argument produces values. If it produces an iterator instead, there's
998 /// an extra layer of indirection. `flat_map()` will remove this extra layer
1001 /// You can think of `flat_map(f)` as the semantic equivalent
1002 /// of [`map`]ping, and then [`flatten`]ing as in `map(f).flatten()`.
1004 /// Another way of thinking about `flat_map()`: [`map`]'s closure returns
1005 /// one item for each element, and `flat_map()`'s closure returns an
1006 /// iterator for each element.
1008 /// [`map`]: #method.map
1009 /// [`flatten`]: #method.flatten
1016 /// let words = ["alpha", "beta", "gamma"];
1018 /// // chars() returns an iterator
1019 /// let merged: String = words.iter()
1020 /// .flat_map(|s| s.chars())
1022 /// assert_eq!(merged, "alphabetagamma");
1025 #[stable(feature = "rust1", since = "1.0.0")]
1026 fn flat_map
<U
, F
>(self, f
: F
) -> FlatMap
<Self, U
, F
>
1027 where Self: Sized
, U
: IntoIterator
, F
: FnMut(Self::Item
) -> U
,
1029 FlatMap { inner: flatten_compat(self.map(f)) }
1032 /// Creates an iterator that flattens nested structure.
1034 /// This is useful when you have an iterator of iterators or an iterator of
1035 /// things that can be turned into iterators and you want to remove one
1036 /// level of indirection.
1043 /// #![feature(iterator_flatten)]
1045 /// let data = vec![vec![1, 2, 3, 4], vec![5, 6]];
1046 /// let flattened = data.into_iter().flatten().collect::<Vec<u8>>();
1047 /// assert_eq!(flattened, &[1, 2, 3, 4, 5, 6]);
1050 /// Mapping and then flattening:
1053 /// #![feature(iterator_flatten)]
1055 /// let words = ["alpha", "beta", "gamma"];
1057 /// // chars() returns an iterator
1058 /// let merged: String = words.iter()
1059 /// .map(|s| s.chars())
1062 /// assert_eq!(merged, "alphabetagamma");
1065 /// You can also rewrite this in terms of [`flat_map()`], which is preferable
1066 /// in this case since it conveys intent more clearly:
1069 /// let words = ["alpha", "beta", "gamma"];
1071 /// // chars() returns an iterator
1072 /// let merged: String = words.iter()
1073 /// .flat_map(|s| s.chars())
1075 /// assert_eq!(merged, "alphabetagamma");
1078 /// Flattening once only removes one level of nesting:
1081 /// #![feature(iterator_flatten)]
1083 /// let d3 = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]];
1085 /// let d2 = d3.iter().flatten().collect::<Vec<_>>();
1086 /// assert_eq!(d2, [&[1, 2], &[3, 4], &[5, 6], &[7, 8]]);
1088 /// let d1 = d3.iter().flatten().flatten().collect::<Vec<_>>();
1089 /// assert_eq!(d1, [&1, &2, &3, &4, &5, &6, &7, &8]);
1092 /// Here we see that `flatten()` does not perform a "deep" flatten.
1093 /// Instead, only one level of nesting is removed. That is, if you
1094 /// `flatten()` a three-dimensional array the result will be
1095 /// two-dimensional and not one-dimensional. To get a one-dimensional
1096 /// structure, you have to `flatten()` again.
1098 /// [`flat_map()`]: #method.flat_map
1100 #[unstable(feature = "iterator_flatten", issue = "48213")]
1101 fn flatten(self) -> Flatten
<Self>
1102 where Self: Sized
, Self::Item
: IntoIterator
{
1103 Flatten { inner: flatten_compat(self) }
1106 /// Creates an iterator which ends after the first [`None`].
1108 /// After an iterator returns [`None`], future calls may or may not yield
1109 /// [`Some(T)`] again. `fuse()` adapts an iterator, ensuring that after a
1110 /// [`None`] is given, it will always return [`None`] forever.
1112 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1113 /// [`Some(T)`]: ../../std/option/enum.Option.html#variant.Some
1120 /// // an iterator which alternates between Some and None
1121 /// struct Alternate {
1125 /// impl Iterator for Alternate {
1126 /// type Item = i32;
1128 /// fn next(&mut self) -> Option<i32> {
1129 /// let val = self.state;
1130 /// self.state = self.state + 1;
1132 /// // if it's even, Some(i32), else None
1133 /// if val % 2 == 0 {
1141 /// let mut iter = Alternate { state: 0 };
1143 /// // we can see our iterator going back and forth
1144 /// assert_eq!(iter.next(), Some(0));
1145 /// assert_eq!(iter.next(), None);
1146 /// assert_eq!(iter.next(), Some(2));
1147 /// assert_eq!(iter.next(), None);
1149 /// // however, once we fuse it...
1150 /// let mut iter = iter.fuse();
1152 /// assert_eq!(iter.next(), Some(4));
1153 /// assert_eq!(iter.next(), None);
1155 /// // it will always return None after the first time.
1156 /// assert_eq!(iter.next(), None);
1157 /// assert_eq!(iter.next(), None);
1158 /// assert_eq!(iter.next(), None);
1161 #[stable(feature = "rust1", since = "1.0.0")]
1162 fn fuse(self) -> Fuse
<Self> where Self: Sized
{
1163 Fuse{iter: self, done: false}
1166 /// Do something with each element of an iterator, passing the value on.
1168 /// When using iterators, you'll often chain several of them together.
1169 /// While working on such code, you might want to check out what's
1170 /// happening at various parts in the pipeline. To do that, insert
1171 /// a call to `inspect()`.
1173 /// It's much more common for `inspect()` to be used as a debugging tool
1174 /// than to exist in your final code, but never say never.
1181 /// let a = [1, 4, 2, 3];
1183 /// // this iterator sequence is complex.
1184 /// let sum = a.iter()
1186 /// .filter(|x| x % 2 == 0)
1187 /// .fold(0, |sum, i| sum + i);
1189 /// println!("{}", sum);
1191 /// // let's add some inspect() calls to investigate what's happening
1192 /// let sum = a.iter()
1194 /// .inspect(|x| println!("about to filter: {}", x))
1195 /// .filter(|x| x % 2 == 0)
1196 /// .inspect(|x| println!("made it through filter: {}", x))
1197 /// .fold(0, |sum, i| sum + i);
1199 /// println!("{}", sum);
1202 /// This will print:
1206 /// about to filter: 1
1207 /// about to filter: 4
1208 /// made it through filter: 4
1209 /// about to filter: 2
1210 /// made it through filter: 2
1211 /// about to filter: 3
1215 #[stable(feature = "rust1", since = "1.0.0")]
1216 fn inspect
<F
>(self, f
: F
) -> Inspect
<Self, F
> where
1217 Self: Sized
, F
: FnMut(&Self::Item
),
1219 Inspect{iter: self, f: f}
1222 /// Borrows an iterator, rather than consuming it.
1224 /// This is useful to allow applying iterator adaptors while still
1225 /// retaining ownership of the original iterator.
1232 /// let a = [1, 2, 3];
1234 /// let iter = a.into_iter();
1236 /// let sum: i32 = iter.take(5).fold(0, |acc, i| acc + i );
1238 /// assert_eq!(sum, 6);
1240 /// // if we try to use iter again, it won't work. The following line
1241 /// // gives "error: use of moved value: `iter`
1242 /// // assert_eq!(iter.next(), None);
1244 /// // let's try that again
1245 /// let a = [1, 2, 3];
1247 /// let mut iter = a.into_iter();
1249 /// // instead, we add in a .by_ref()
1250 /// let sum: i32 = iter.by_ref().take(2).fold(0, |acc, i| acc + i );
1252 /// assert_eq!(sum, 3);
1254 /// // now this is just fine:
1255 /// assert_eq!(iter.next(), Some(&3));
1256 /// assert_eq!(iter.next(), None);
1258 #[stable(feature = "rust1", since = "1.0.0")]
1259 fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
1261 /// Transforms an iterator into a collection.
1263 /// `collect()` can take anything iterable, and turn it into a relevant
1264 /// collection. This is one of the more powerful methods in the standard
1265 /// library, used in a variety of contexts.
1267 /// The most basic pattern in which `collect()` is used is to turn one
1268 /// collection into another. You take a collection, call [`iter`] on it,
1269 /// do a bunch of transformations, and then `collect()` at the end.
1271 /// One of the keys to `collect()`'s power is that many things you might
1272 /// not think of as 'collections' actually are. For example, a [`String`]
1273 /// is a collection of [`char`]s. And a collection of
1274 /// [`Result<T, E>`][`Result`] can be thought of as single
1275 /// [`Result`]`<Collection<T>, E>`. See the examples below for more.
1277 /// Because `collect()` is so general, it can cause problems with type
1278 /// inference. As such, `collect()` is one of the few times you'll see
1279 /// the syntax affectionately known as the 'turbofish': `::<>`. This
1280 /// helps the inference algorithm understand specifically which collection
1281 /// you're trying to collect into.
1288 /// let a = [1, 2, 3];
1290 /// let doubled: Vec<i32> = a.iter()
1291 /// .map(|&x| x * 2)
1294 /// assert_eq!(vec![2, 4, 6], doubled);
1297 /// Note that we needed the `: Vec<i32>` on the left-hand side. This is because
1298 /// we could collect into, for example, a [`VecDeque<T>`] instead:
1300 /// [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html
1303 /// use std::collections::VecDeque;
1305 /// let a = [1, 2, 3];
1307 /// let doubled: VecDeque<i32> = a.iter().map(|&x| x * 2).collect();
1309 /// assert_eq!(2, doubled[0]);
1310 /// assert_eq!(4, doubled[1]);
1311 /// assert_eq!(6, doubled[2]);
1314 /// Using the 'turbofish' instead of annotating `doubled`:
1317 /// let a = [1, 2, 3];
1319 /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<i32>>();
1321 /// assert_eq!(vec![2, 4, 6], doubled);
1324 /// Because `collect()` only cares about what you're collecting into, you can
1325 /// still use a partial type hint, `_`, with the turbofish:
1328 /// let a = [1, 2, 3];
1330 /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<_>>();
1332 /// assert_eq!(vec![2, 4, 6], doubled);
1335 /// Using `collect()` to make a [`String`]:
1338 /// let chars = ['g', 'd', 'k', 'k', 'n'];
1340 /// let hello: String = chars.iter()
1341 /// .map(|&x| x as u8)
1342 /// .map(|x| (x + 1) as char)
1345 /// assert_eq!("hello", hello);
1348 /// If you have a list of [`Result<T, E>`][`Result`]s, you can use `collect()` to
1349 /// see if any of them failed:
1352 /// let results = [Ok(1), Err("nope"), Ok(3), Err("bad")];
1354 /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect();
1356 /// // gives us the first error
1357 /// assert_eq!(Err("nope"), result);
1359 /// let results = [Ok(1), Ok(3)];
1361 /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect();
1363 /// // gives us the list of answers
1364 /// assert_eq!(Ok(vec![1, 3]), result);
1367 /// [`iter`]: ../../std/iter/trait.Iterator.html#tymethod.next
1368 /// [`String`]: ../../std/string/struct.String.html
1369 /// [`char`]: ../../std/primitive.char.html
1370 /// [`Result`]: ../../std/result/enum.Result.html
1372 #[stable(feature = "rust1", since = "1.0.0")]
1373 #[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"]
1374 fn collect
<B
: FromIterator
<Self::Item
>>(self) -> B
where Self: Sized
{
1375 FromIterator
::from_iter(self)
1378 /// Consumes an iterator, creating two collections from it.
1380 /// The predicate passed to `partition()` can return `true`, or `false`.
1381 /// `partition()` returns a pair, all of the elements for which it returned
1382 /// `true`, and all of the elements for which it returned `false`.
1389 /// let a = [1, 2, 3];
1391 /// let (even, odd): (Vec<i32>, Vec<i32>) = a
1393 /// .partition(|&n| n % 2 == 0);
1395 /// assert_eq!(even, vec![2]);
1396 /// assert_eq!(odd, vec![1, 3]);
1398 #[stable(feature = "rust1", since = "1.0.0")]
1399 fn partition
<B
, F
>(self, mut f
: F
) -> (B
, B
) where
1401 B
: Default
+ Extend
<Self::Item
>,
1402 F
: FnMut(&Self::Item
) -> bool
1404 let mut left
: B
= Default
::default();
1405 let mut right
: B
= Default
::default();
1409 left
.extend(Some(x
))
1411 right
.extend(Some(x
))
1418 /// An iterator method that applies a function as long as it returns
1419 /// successfully, producing a single, final value.
1421 /// `try_fold()` takes two arguments: an initial value, and a closure with
1422 /// two arguments: an 'accumulator', and an element. The closure either
1423 /// returns successfully, with the value that the accumulator should have
1424 /// for the next iteration, or it returns failure, with an error value that
1425 /// is propagated back to the caller immediately (short-circuiting).
1427 /// The initial value is the value the accumulator will have on the first
1428 /// call. If applying the closure succeeded against every element of the
1429 /// iterator, `try_fold()` returns the final accumulator as success.
1431 /// Folding is useful whenever you have a collection of something, and want
1432 /// to produce a single value from it.
1434 /// # Note to Implementors
1436 /// Most of the other (forward) methods have default implementations in
1437 /// terms of this one, so try to implement this explicitly if it can
1438 /// do something better than the default `for` loop implementation.
1440 /// In particular, try to have this call `try_fold()` on the internal parts
1441 /// from which this iterator is composed. If multiple calls are needed,
1442 /// the `?` operator may be convenient for chaining the accumulator value
1443 /// along, but beware any invariants that need to be upheld before those
1444 /// early returns. This is a `&mut self` method, so iteration needs to be
1445 /// resumable after hitting an error here.
1452 /// let a = [1, 2, 3];
1454 /// // the checked sum of all of the elements of the array
1455 /// let sum = a.iter().try_fold(0i8, |acc, &x| acc.checked_add(x));
1457 /// assert_eq!(sum, Some(6));
1460 /// Short-circuiting:
1463 /// let a = [10, 20, 30, 100, 40, 50];
1464 /// let mut it = a.iter();
1466 /// // This sum overflows when adding the 100 element
1467 /// let sum = it.try_fold(0i8, |acc, &x| acc.checked_add(x));
1468 /// assert_eq!(sum, None);
1470 /// // Because it short-circuited, the remaining elements are still
1471 /// // available through the iterator.
1472 /// assert_eq!(it.len(), 2);
1473 /// assert_eq!(it.next(), Some(&40));
1476 #[stable(feature = "iterator_try_fold", since = "1.27.0")]
1477 fn try_fold
<B
, F
, R
>(&mut self, init
: B
, mut f
: F
) -> R
where
1478 Self: Sized
, F
: FnMut(B
, Self::Item
) -> R
, R
: Try
<Ok
=B
>
1480 let mut accum
= init
;
1481 while let Some(x
) = self.next() {
1482 accum
= f(accum
, x
)?
;
1487 /// An iterator method that applies a fallible function to each item in the
1488 /// iterator, stopping at the first error and returning that error.
1490 /// This can also be thought of as the fallible form of [`for_each()`]
1491 /// or as the stateless version of [`try_fold()`].
1493 /// [`for_each()`]: #method.for_each
1494 /// [`try_fold()`]: #method.try_fold
1499 /// use std::fs::rename;
1500 /// use std::io::{stdout, Write};
1501 /// use std::path::Path;
1503 /// let data = ["no_tea.txt", "stale_bread.json", "torrential_rain.png"];
1505 /// let res = data.iter().try_for_each(|x| writeln!(stdout(), "{}", x));
1506 /// assert!(res.is_ok());
1508 /// let mut it = data.iter().cloned();
1509 /// let res = it.try_for_each(|x| rename(x, Path::new(x).with_extension("old")));
1510 /// assert!(res.is_err());
1511 /// // It short-circuited, so the remaining items are still in the iterator:
1512 /// assert_eq!(it.next(), Some("stale_bread.json"));
1515 #[stable(feature = "iterator_try_fold", since = "1.27.0")]
1516 fn try_for_each
<F
, R
>(&mut self, mut f
: F
) -> R
where
1517 Self: Sized
, F
: FnMut(Self::Item
) -> R
, R
: Try
<Ok
=()>
1519 self.try_fold((), move |(), x
| f(x
))
1522 /// An iterator method that applies a function, producing a single, final value.
1524 /// `fold()` takes two arguments: an initial value, and a closure with two
1525 /// arguments: an 'accumulator', and an element. The closure returns the value that
1526 /// the accumulator should have for the next iteration.
1528 /// The initial value is the value the accumulator will have on the first
1531 /// After applying this closure to every element of the iterator, `fold()`
1532 /// returns the accumulator.
1534 /// This operation is sometimes called 'reduce' or 'inject'.
1536 /// Folding is useful whenever you have a collection of something, and want
1537 /// to produce a single value from it.
1539 /// Note: `fold()`, and similar methods that traverse the entire iterator,
1540 /// may not terminate for infinite iterators, even on traits for which a
1541 /// result is determinable in finite time.
1548 /// let a = [1, 2, 3];
1550 /// // the sum of all of the elements of the array
1551 /// let sum = a.iter().fold(0, |acc, x| acc + x);
1553 /// assert_eq!(sum, 6);
1556 /// Let's walk through each step of the iteration here:
1558 /// | element | acc | x | result |
1559 /// |---------|-----|---|--------|
1561 /// | 1 | 0 | 1 | 1 |
1562 /// | 2 | 1 | 2 | 3 |
1563 /// | 3 | 3 | 3 | 6 |
1565 /// And so, our final result, `6`.
1567 /// It's common for people who haven't used iterators a lot to
1568 /// use a `for` loop with a list of things to build up a result. Those
1569 /// can be turned into `fold()`s:
1571 /// [`for`]: ../../book/first-edition/loops.html#for
1574 /// let numbers = [1, 2, 3, 4, 5];
1576 /// let mut result = 0;
1579 /// for i in &numbers {
1580 /// result = result + i;
1584 /// let result2 = numbers.iter().fold(0, |acc, &x| acc + x);
1586 /// // they're the same
1587 /// assert_eq!(result, result2);
1590 #[stable(feature = "rust1", since = "1.0.0")]
1591 fn fold
<B
, F
>(mut self, init
: B
, mut f
: F
) -> B
where
1592 Self: Sized
, F
: FnMut(B
, Self::Item
) -> B
,
1594 self.try_fold(init
, move |acc
, x
| AlwaysOk(f(acc
, x
))).0
1597 /// Tests if every element of the iterator matches a predicate.
1599 /// `all()` takes a closure that returns `true` or `false`. It applies
1600 /// this closure to each element of the iterator, and if they all return
1601 /// `true`, then so does `all()`. If any of them return `false`, it
1602 /// returns `false`.
1604 /// `all()` is short-circuiting; in other words, it will stop processing
1605 /// as soon as it finds a `false`, given that no matter what else happens,
1606 /// the result will also be `false`.
1608 /// An empty iterator returns `true`.
1615 /// let a = [1, 2, 3];
1617 /// assert!(a.iter().all(|&x| x > 0));
1619 /// assert!(!a.iter().all(|&x| x > 2));
1622 /// Stopping at the first `false`:
1625 /// let a = [1, 2, 3];
1627 /// let mut iter = a.iter();
1629 /// assert!(!iter.all(|&x| x != 2));
1631 /// // we can still use `iter`, as there are more elements.
1632 /// assert_eq!(iter.next(), Some(&3));
1635 #[stable(feature = "rust1", since = "1.0.0")]
1636 fn all
<F
>(&mut self, mut f
: F
) -> bool
where
1637 Self: Sized
, F
: FnMut(Self::Item
) -> bool
1639 self.try_for_each(move |x
| {
1640 if f(x
) { LoopState::Continue(()) }
1641 else { LoopState::Break(()) }
1642 }) == LoopState
::Continue(())
1645 /// Tests if any element of the iterator matches a predicate.
1647 /// `any()` takes a closure that returns `true` or `false`. It applies
1648 /// this closure to each element of the iterator, and if any of them return
1649 /// `true`, then so does `any()`. If they all return `false`, it
1650 /// returns `false`.
1652 /// `any()` is short-circuiting; in other words, it will stop processing
1653 /// as soon as it finds a `true`, given that no matter what else happens,
1654 /// the result will also be `true`.
1656 /// An empty iterator returns `false`.
1663 /// let a = [1, 2, 3];
1665 /// assert!(a.iter().any(|&x| x > 0));
1667 /// assert!(!a.iter().any(|&x| x > 5));
1670 /// Stopping at the first `true`:
1673 /// let a = [1, 2, 3];
1675 /// let mut iter = a.iter();
1677 /// assert!(iter.any(|&x| x != 2));
1679 /// // we can still use `iter`, as there are more elements.
1680 /// assert_eq!(iter.next(), Some(&2));
1683 #[stable(feature = "rust1", since = "1.0.0")]
1684 fn any
<F
>(&mut self, mut f
: F
) -> bool
where
1686 F
: FnMut(Self::Item
) -> bool
1688 self.try_for_each(move |x
| {
1689 if f(x
) { LoopState::Break(()) }
1690 else { LoopState::Continue(()) }
1691 }) == LoopState
::Break(())
1694 /// Searches for an element of an iterator that satisfies a predicate.
1696 /// `find()` takes a closure that returns `true` or `false`. It applies
1697 /// this closure to each element of the iterator, and if any of them return
1698 /// `true`, then `find()` returns [`Some(element)`]. If they all return
1699 /// `false`, it returns [`None`].
1701 /// `find()` is short-circuiting; in other words, it will stop processing
1702 /// as soon as the closure returns `true`.
1704 /// Because `find()` takes a reference, and many iterators iterate over
1705 /// references, this leads to a possibly confusing situation where the
1706 /// argument is a double reference. You can see this effect in the
1707 /// examples below, with `&&x`.
1709 /// [`Some(element)`]: ../../std/option/enum.Option.html#variant.Some
1710 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1717 /// let a = [1, 2, 3];
1719 /// assert_eq!(a.iter().find(|&&x| x == 2), Some(&2));
1721 /// assert_eq!(a.iter().find(|&&x| x == 5), None);
1724 /// Stopping at the first `true`:
1727 /// let a = [1, 2, 3];
1729 /// let mut iter = a.iter();
1731 /// assert_eq!(iter.find(|&&x| x == 2), Some(&2));
1733 /// // we can still use `iter`, as there are more elements.
1734 /// assert_eq!(iter.next(), Some(&3));
1737 #[stable(feature = "rust1", since = "1.0.0")]
1738 fn find
<P
>(&mut self, mut predicate
: P
) -> Option
<Self::Item
> where
1740 P
: FnMut(&Self::Item
) -> bool
,
1742 self.try_for_each(move |x
| {
1743 if predicate(&x
) { LoopState::Break(x) }
1744 else { LoopState::Continue(()) }
1748 /// Applies function to the elements of iterator and returns
1749 /// the first non-none result.
1751 /// `iter.find_map(f)` is equivalent to `iter.filter_map(f).next()`.
1757 /// #![feature(iterator_find_map)]
1758 /// let a = ["lol", "NaN", "2", "5"];
1760 /// let mut first_number = a.iter().find_map(|s| s.parse().ok());
1762 /// assert_eq!(first_number, Some(2));
1765 #[unstable(feature = "iterator_find_map",
1766 reason
= "unstable new API",
1768 fn find_map
<B
, F
>(&mut self, mut f
: F
) -> Option
<B
> where
1770 F
: FnMut(Self::Item
) -> Option
<B
>,
1772 self.try_for_each(move |x
| {
1774 Some(x
) => LoopState
::Break(x
),
1775 None
=> LoopState
::Continue(()),
1780 /// Searches for an element in an iterator, returning its index.
1782 /// `position()` takes a closure that returns `true` or `false`. It applies
1783 /// this closure to each element of the iterator, and if one of them
1784 /// returns `true`, then `position()` returns [`Some(index)`]. If all of
1785 /// them return `false`, it returns [`None`].
1787 /// `position()` is short-circuiting; in other words, it will stop
1788 /// processing as soon as it finds a `true`.
1790 /// # Overflow Behavior
1792 /// The method does no guarding against overflows, so if there are more
1793 /// than [`usize::MAX`] non-matching elements, it either produces the wrong
1794 /// result or panics. If debug assertions are enabled, a panic is
1799 /// This function might panic if the iterator has more than `usize::MAX`
1800 /// non-matching elements.
1802 /// [`Some(index)`]: ../../std/option/enum.Option.html#variant.Some
1803 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1804 /// [`usize::MAX`]: ../../std/usize/constant.MAX.html
1811 /// let a = [1, 2, 3];
1813 /// assert_eq!(a.iter().position(|&x| x == 2), Some(1));
1815 /// assert_eq!(a.iter().position(|&x| x == 5), None);
1818 /// Stopping at the first `true`:
1821 /// let a = [1, 2, 3, 4];
1823 /// let mut iter = a.iter();
1825 /// assert_eq!(iter.position(|&x| x >= 2), Some(1));
1827 /// // we can still use `iter`, as there are more elements.
1828 /// assert_eq!(iter.next(), Some(&3));
1830 /// // The returned index depends on iterator state
1831 /// assert_eq!(iter.position(|&x| x == 4), Some(0));
1835 #[rustc_inherit_overflow_checks]
1836 #[stable(feature = "rust1", since = "1.0.0")]
1837 fn position
<P
>(&mut self, mut predicate
: P
) -> Option
<usize> where
1839 P
: FnMut(Self::Item
) -> bool
,
1841 // The addition might panic on overflow
1842 self.try_fold(0, move |i
, x
| {
1843 if predicate(x
) { LoopState::Break(i) }
1844 else { LoopState::Continue(i + 1) }
1848 /// Searches for an element in an iterator from the right, returning its
1851 /// `rposition()` takes a closure that returns `true` or `false`. It applies
1852 /// this closure to each element of the iterator, starting from the end,
1853 /// and if one of them returns `true`, then `rposition()` returns
1854 /// [`Some(index)`]. If all of them return `false`, it returns [`None`].
1856 /// `rposition()` is short-circuiting; in other words, it will stop
1857 /// processing as soon as it finds a `true`.
1859 /// [`Some(index)`]: ../../std/option/enum.Option.html#variant.Some
1860 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1867 /// let a = [1, 2, 3];
1869 /// assert_eq!(a.iter().rposition(|&x| x == 3), Some(2));
1871 /// assert_eq!(a.iter().rposition(|&x| x == 5), None);
1874 /// Stopping at the first `true`:
1877 /// let a = [1, 2, 3];
1879 /// let mut iter = a.iter();
1881 /// assert_eq!(iter.rposition(|&x| x == 2), Some(1));
1883 /// // we can still use `iter`, as there are more elements.
1884 /// assert_eq!(iter.next(), Some(&1));
1887 #[stable(feature = "rust1", since = "1.0.0")]
1888 fn rposition
<P
>(&mut self, mut predicate
: P
) -> Option
<usize> where
1889 P
: FnMut(Self::Item
) -> bool
,
1890 Self: Sized
+ ExactSizeIterator
+ DoubleEndedIterator
1892 // No need for an overflow check here, because `ExactSizeIterator`
1893 // implies that the number of elements fits into a `usize`.
1895 self.try_rfold(n
, move |i
, x
| {
1897 if predicate(x
) { LoopState::Break(i) }
1898 else { LoopState::Continue(i) }
1902 /// Returns the maximum element of an iterator.
1904 /// If several elements are equally maximum, the last element is
1905 /// returned. If the iterator is empty, [`None`] is returned.
1907 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1914 /// let a = [1, 2, 3];
1915 /// let b: Vec<u32> = Vec::new();
1917 /// assert_eq!(a.iter().max(), Some(&3));
1918 /// assert_eq!(b.iter().max(), None);
1921 #[stable(feature = "rust1", since = "1.0.0")]
1922 fn max(self) -> Option
<Self::Item
> where Self: Sized
, Self::Item
: Ord
1926 // switch to y even if it is only equal, to preserve
1928 |_
, x
, _
, y
| *x
<= *y
)
1932 /// Returns the minimum element of an iterator.
1934 /// If several elements are equally minimum, the first element is
1935 /// returned. If the iterator is empty, [`None`] is returned.
1937 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1944 /// let a = [1, 2, 3];
1945 /// let b: Vec<u32> = Vec::new();
1947 /// assert_eq!(a.iter().min(), Some(&1));
1948 /// assert_eq!(b.iter().min(), None);
1951 #[stable(feature = "rust1", since = "1.0.0")]
1952 fn min(self) -> Option
<Self::Item
> where Self: Sized
, Self::Item
: Ord
1956 // only switch to y if it is strictly smaller, to
1957 // preserve stability.
1958 |_
, x
, _
, y
| *x
> *y
)
1962 /// Returns the element that gives the maximum value from the
1963 /// specified function.
1965 /// If several elements are equally maximum, the last element is
1966 /// returned. If the iterator is empty, [`None`] is returned.
1968 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1973 /// let a = [-3_i32, 0, 1, 5, -10];
1974 /// assert_eq!(*a.iter().max_by_key(|x| x.abs()).unwrap(), -10);
1977 #[stable(feature = "iter_cmp_by_key", since = "1.6.0")]
1978 fn max_by_key
<B
: Ord
, F
>(self, f
: F
) -> Option
<Self::Item
>
1979 where Self: Sized
, F
: FnMut(&Self::Item
) -> B
,
1983 // switch to y even if it is only equal, to preserve
1985 |x_p
, _
, y_p
, _
| x_p
<= y_p
)
1989 /// Returns the element that gives the maximum value with respect to the
1990 /// specified comparison function.
1992 /// If several elements are equally maximum, the last element is
1993 /// returned. If the iterator is empty, [`None`] is returned.
1995 /// [`None`]: ../../std/option/enum.Option.html#variant.None
2000 /// let a = [-3_i32, 0, 1, 5, -10];
2001 /// assert_eq!(*a.iter().max_by(|x, y| x.cmp(y)).unwrap(), 5);
2004 #[stable(feature = "iter_max_by", since = "1.15.0")]
2005 fn max_by
<F
>(self, mut compare
: F
) -> Option
<Self::Item
>
2006 where Self: Sized
, F
: FnMut(&Self::Item
, &Self::Item
) -> Ordering
,
2010 // switch to y even if it is only equal, to preserve
2012 |_
, x
, _
, y
| Ordering
::Greater
!= compare(x
, y
))
2016 /// Returns the element that gives the minimum value from the
2017 /// specified function.
2019 /// If several elements are equally minimum, the first element is
2020 /// returned. If the iterator is empty, [`None`] is returned.
2022 /// [`None`]: ../../std/option/enum.Option.html#variant.None
2027 /// let a = [-3_i32, 0, 1, 5, -10];
2028 /// assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0);
2030 #[stable(feature = "iter_cmp_by_key", since = "1.6.0")]
2031 fn min_by_key
<B
: Ord
, F
>(self, f
: F
) -> Option
<Self::Item
>
2032 where Self: Sized
, F
: FnMut(&Self::Item
) -> B
,
2036 // only switch to y if it is strictly smaller, to
2037 // preserve stability.
2038 |x_p
, _
, y_p
, _
| x_p
> y_p
)
2042 /// Returns the element that gives the minimum value with respect to the
2043 /// specified comparison function.
2045 /// If several elements are equally minimum, the first element is
2046 /// returned. If the iterator is empty, [`None`] is returned.
2048 /// [`None`]: ../../std/option/enum.Option.html#variant.None
2053 /// let a = [-3_i32, 0, 1, 5, -10];
2054 /// assert_eq!(*a.iter().min_by(|x, y| x.cmp(y)).unwrap(), -10);
2057 #[stable(feature = "iter_min_by", since = "1.15.0")]
2058 fn min_by
<F
>(self, mut compare
: F
) -> Option
<Self::Item
>
2059 where Self: Sized
, F
: FnMut(&Self::Item
, &Self::Item
) -> Ordering
,
2063 // switch to y even if it is strictly smaller, to
2064 // preserve stability.
2065 |_
, x
, _
, y
| Ordering
::Greater
== compare(x
, y
))
2070 /// Reverses an iterator's direction.
2072 /// Usually, iterators iterate from left to right. After using `rev()`,
2073 /// an iterator will instead iterate from right to left.
2075 /// This is only possible if the iterator has an end, so `rev()` only
2076 /// works on [`DoubleEndedIterator`]s.
2078 /// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html
2083 /// let a = [1, 2, 3];
2085 /// let mut iter = a.iter().rev();
2087 /// assert_eq!(iter.next(), Some(&3));
2088 /// assert_eq!(iter.next(), Some(&2));
2089 /// assert_eq!(iter.next(), Some(&1));
2091 /// assert_eq!(iter.next(), None);
2094 #[stable(feature = "rust1", since = "1.0.0")]
2095 fn rev(self) -> Rev
<Self> where Self: Sized
+ DoubleEndedIterator
{
2099 /// Converts an iterator of pairs into a pair of containers.
2101 /// `unzip()` consumes an entire iterator of pairs, producing two
2102 /// collections: one from the left elements of the pairs, and one
2103 /// from the right elements.
2105 /// This function is, in some sense, the opposite of [`zip`].
2107 /// [`zip`]: #method.zip
2114 /// let a = [(1, 2), (3, 4)];
2116 /// let (left, right): (Vec<_>, Vec<_>) = a.iter().cloned().unzip();
2118 /// assert_eq!(left, [1, 3]);
2119 /// assert_eq!(right, [2, 4]);
2121 #[stable(feature = "rust1", since = "1.0.0")]
2122 fn unzip
<A
, B
, FromA
, FromB
>(self) -> (FromA
, FromB
) where
2123 FromA
: Default
+ Extend
<A
>,
2124 FromB
: Default
+ Extend
<B
>,
2125 Self: Sized
+ Iterator
<Item
=(A
, B
)>,
2127 let mut ts
: FromA
= Default
::default();
2128 let mut us
: FromB
= Default
::default();
2130 self.for_each(|(t
, u
)| {
2138 /// Creates an iterator which [`clone`]s all of its elements.
2140 /// This is useful when you have an iterator over `&T`, but you need an
2141 /// iterator over `T`.
2143 /// [`clone`]: ../../std/clone/trait.Clone.html#tymethod.clone
2150 /// let a = [1, 2, 3];
2152 /// let v_cloned: Vec<_> = a.iter().cloned().collect();
2154 /// // cloned is the same as .map(|&x| x), for integers
2155 /// let v_map: Vec<_> = a.iter().map(|&x| x).collect();
2157 /// assert_eq!(v_cloned, vec![1, 2, 3]);
2158 /// assert_eq!(v_map, vec![1, 2, 3]);
2160 #[stable(feature = "rust1", since = "1.0.0")]
2161 fn cloned
<'a
, T
: 'a
>(self) -> Cloned
<Self>
2162 where Self: Sized
+ Iterator
<Item
=&'a T
>, T
: Clone
2167 /// Repeats an iterator endlessly.
2169 /// Instead of stopping at [`None`], the iterator will instead start again,
2170 /// from the beginning. After iterating again, it will start at the
2171 /// beginning again. And again. And again. Forever.
2173 /// [`None`]: ../../std/option/enum.Option.html#variant.None
2180 /// let a = [1, 2, 3];
2182 /// let mut it = a.iter().cycle();
2184 /// assert_eq!(it.next(), Some(&1));
2185 /// assert_eq!(it.next(), Some(&2));
2186 /// assert_eq!(it.next(), Some(&3));
2187 /// assert_eq!(it.next(), Some(&1));
2188 /// assert_eq!(it.next(), Some(&2));
2189 /// assert_eq!(it.next(), Some(&3));
2190 /// assert_eq!(it.next(), Some(&1));
2192 #[stable(feature = "rust1", since = "1.0.0")]
2194 fn cycle(self) -> Cycle
<Self> where Self: Sized
+ Clone
{
2195 Cycle{orig: self.clone(), iter: self}
2198 /// Sums the elements of an iterator.
2200 /// Takes each element, adds them together, and returns the result.
2202 /// An empty iterator returns the zero value of the type.
2206 /// When calling `sum()` and a primitive integer type is being returned, this
2207 /// method will panic if the computation overflows and debug assertions are
2215 /// let a = [1, 2, 3];
2216 /// let sum: i32 = a.iter().sum();
2218 /// assert_eq!(sum, 6);
2220 #[stable(feature = "iter_arith", since = "1.11.0")]
2221 fn sum
<S
>(self) -> S
2228 /// Iterates over the entire iterator, multiplying all the elements
2230 /// An empty iterator returns the one value of the type.
2234 /// When calling `product()` and a primitive integer type is being returned,
2235 /// method will panic if the computation overflows and debug assertions are
2241 /// fn factorial(n: u32) -> u32 {
2242 /// (1..).take_while(|&i| i <= n).product()
2244 /// assert_eq!(factorial(0), 1);
2245 /// assert_eq!(factorial(1), 1);
2246 /// assert_eq!(factorial(5), 120);
2248 #[stable(feature = "iter_arith", since = "1.11.0")]
2249 fn product
<P
>(self) -> P
2251 P
: Product
<Self::Item
>,
2253 Product
::product(self)
2256 /// Lexicographically compares the elements of this `Iterator` with those
2258 #[stable(feature = "iter_order", since = "1.5.0")]
2259 fn cmp
<I
>(mut self, other
: I
) -> Ordering
where
2260 I
: IntoIterator
<Item
= Self::Item
>,
2264 let mut other
= other
.into_iter();
2267 let x
= match self.next() {
2268 None
=> if other
.next().is_none() {
2269 return Ordering
::Equal
2271 return Ordering
::Less
2276 let y
= match other
.next() {
2277 None
=> return Ordering
::Greater
,
2282 Ordering
::Equal
=> (),
2283 non_eq
=> return non_eq
,
2288 /// Lexicographically compares the elements of this `Iterator` with those
2290 #[stable(feature = "iter_order", since = "1.5.0")]
2291 fn partial_cmp
<I
>(mut self, other
: I
) -> Option
<Ordering
> where
2293 Self::Item
: PartialOrd
<I
::Item
>,
2296 let mut other
= other
.into_iter();
2299 let x
= match self.next() {
2300 None
=> if other
.next().is_none() {
2301 return Some(Ordering
::Equal
)
2303 return Some(Ordering
::Less
)
2308 let y
= match other
.next() {
2309 None
=> return Some(Ordering
::Greater
),
2313 match x
.partial_cmp(&y
) {
2314 Some(Ordering
::Equal
) => (),
2315 non_eq
=> return non_eq
,
2320 /// Determines if the elements of this `Iterator` are equal to those of
2322 #[stable(feature = "iter_order", since = "1.5.0")]
2323 fn eq
<I
>(mut self, other
: I
) -> bool
where
2325 Self::Item
: PartialEq
<I
::Item
>,
2328 let mut other
= other
.into_iter();
2331 let x
= match self.next() {
2332 None
=> return other
.next().is_none(),
2336 let y
= match other
.next() {
2337 None
=> return false,
2341 if x
!= y { return false }
2345 /// Determines if the elements of this `Iterator` are unequal to those of
2347 #[stable(feature = "iter_order", since = "1.5.0")]
2348 fn ne
<I
>(mut self, other
: I
) -> bool
where
2350 Self::Item
: PartialEq
<I
::Item
>,
2353 let mut other
= other
.into_iter();
2356 let x
= match self.next() {
2357 None
=> return other
.next().is_some(),
2361 let y
= match other
.next() {
2362 None
=> return true,
2366 if x
!= y { return true }
2370 /// Determines if the elements of this `Iterator` are lexicographically
2371 /// less than those of another.
2372 #[stable(feature = "iter_order", since = "1.5.0")]
2373 fn lt
<I
>(mut self, other
: I
) -> bool
where
2375 Self::Item
: PartialOrd
<I
::Item
>,
2378 let mut other
= other
.into_iter();
2381 let x
= match self.next() {
2382 None
=> return other
.next().is_some(),
2386 let y
= match other
.next() {
2387 None
=> return false,
2391 match x
.partial_cmp(&y
) {
2392 Some(Ordering
::Less
) => return true,
2393 Some(Ordering
::Equal
) => (),
2394 Some(Ordering
::Greater
) => return false,
2395 None
=> return false,
2400 /// Determines if the elements of this `Iterator` are lexicographically
2401 /// less or equal to those of another.
2402 #[stable(feature = "iter_order", since = "1.5.0")]
2403 fn le
<I
>(mut self, other
: I
) -> bool
where
2405 Self::Item
: PartialOrd
<I
::Item
>,
2408 let mut other
= other
.into_iter();
2411 let x
= match self.next() {
2412 None
=> { other.next(); return true; }
,
2416 let y
= match other
.next() {
2417 None
=> return false,
2421 match x
.partial_cmp(&y
) {
2422 Some(Ordering
::Less
) => return true,
2423 Some(Ordering
::Equal
) => (),
2424 Some(Ordering
::Greater
) => return false,
2425 None
=> return false,
2430 /// Determines if the elements of this `Iterator` are lexicographically
2431 /// greater than those of another.
2432 #[stable(feature = "iter_order", since = "1.5.0")]
2433 fn gt
<I
>(mut self, other
: I
) -> bool
where
2435 Self::Item
: PartialOrd
<I
::Item
>,
2438 let mut other
= other
.into_iter();
2441 let x
= match self.next() {
2442 None
=> { other.next(); return false; }
,
2446 let y
= match other
.next() {
2447 None
=> return true,
2451 match x
.partial_cmp(&y
) {
2452 Some(Ordering
::Less
) => return false,
2453 Some(Ordering
::Equal
) => (),
2454 Some(Ordering
::Greater
) => return true,
2455 None
=> return false,
2460 /// Determines if the elements of this `Iterator` are lexicographically
2461 /// greater than or equal to those of another.
2462 #[stable(feature = "iter_order", since = "1.5.0")]
2463 fn ge
<I
>(mut self, other
: I
) -> bool
where
2465 Self::Item
: PartialOrd
<I
::Item
>,
2468 let mut other
= other
.into_iter();
2471 let x
= match self.next() {
2472 None
=> return other
.next().is_none(),
2476 let y
= match other
.next() {
2477 None
=> return true,
2481 match x
.partial_cmp(&y
) {
2482 Some(Ordering
::Less
) => return false,
2483 Some(Ordering
::Equal
) => (),
2484 Some(Ordering
::Greater
) => return true,
2485 None
=> return false,
2491 /// Select an element from an iterator based on the given "projection"
2492 /// and "comparison" function.
2494 /// This is an idiosyncratic helper to try to factor out the
2495 /// commonalities of {max,min}{,_by}. In particular, this avoids
2496 /// having to implement optimizations several times.
2498 fn select_fold1
<I
, B
, FProj
, FCmp
>(mut it
: I
,
2500 mut f_cmp
: FCmp
) -> Option
<(B
, I
::Item
)>
2502 FProj
: FnMut(&I
::Item
) -> B
,
2503 FCmp
: FnMut(&B
, &I
::Item
, &B
, &I
::Item
) -> bool
2505 // start with the first element as our selection. This avoids
2506 // having to use `Option`s inside the loop, translating to a
2507 // sizeable performance gain (6x in one case).
2508 it
.next().map(|first
| {
2509 let first_p
= f_proj(&first
);
2511 it
.fold((first_p
, first
), |(sel_p
, sel
), x
| {
2512 let x_p
= f_proj(&x
);
2513 if f_cmp(&sel_p
, &sel
, &x_p
, &x
) {
2522 #[stable(feature = "rust1", since = "1.0.0")]
2523 impl<'a
, I
: Iterator
+ ?Sized
> Iterator
for &'a
mut I
{
2524 type Item
= I
::Item
;
2525 fn next(&mut self) -> Option
<I
::Item
> { (**self).next() }
2526 fn size_hint(&self) -> (usize, Option
<usize>) { (**self).size_hint() }
2527 fn nth(&mut self, n
: usize) -> Option
<Self::Item
> {