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diff --git a/src/libcore/iter/iterator.rs b/src/libcore/iter/iterator.rs new file mode 100644 index 00000000000..0cc83d42ce0 --- /dev/null +++ b/src/libcore/iter/iterator.rs @@ -0,0 +1,2109 @@ +// Copyright 2013-2016 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or +// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license +// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +use clone::Clone; +use cmp::{Ord, PartialOrd, PartialEq, Ordering}; +use default::Default; +use marker; +use num::{Zero, One}; +use ops::{Add, FnMut, Mul}; +use option::Option::{self, Some, None}; +use marker::Sized; + +use super::{Chain, Cycle, Cloned, Enumerate, Filter, FilterMap, FlatMap, Fuse, Inspect, Map, Peekable, Scan, Skip, SkipWhile, Take, TakeWhile, Rev, Zip}; +use super::ChainState; +use super::{DoubleEndedIterator, ExactSizeIterator, Extend, FromIterator, IntoIterator}; + +fn _assert_is_object_safe(_: &Iterator<Item=()>) {} + +/// An interface for dealing with iterators. +/// +/// This is the main iterator trait. For more about the concept of iterators +/// generally, please see the [module-level documentation]. In particular, you +/// may want to know how to [implement `Iterator`][impl]. +/// +/// [module-level documentation]: index.html +/// [impl]: index.html#implementing-iterator +#[stable(feature = "rust1", since = "1.0.0")] +#[rustc_on_unimplemented = "`{Self}` is not an iterator; maybe try calling \ + `.iter()` or a similar method"] +pub trait Iterator { + /// The type of the elements being iterated over. + #[stable(feature = "rust1", since = "1.0.0")] + type Item; + + /// Advances the iterator and returns the next value. + /// + /// Returns `None` when iteration is finished. Individual iterator + /// implementations may choose to resume iteration, and so calling `next()` + /// again may or may not eventually start returning `Some(Item)` again at some + /// point. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.iter(); + /// + /// // A call to next() returns the next value... + /// assert_eq!(Some(&1), iter.next()); + /// assert_eq!(Some(&2), iter.next()); + /// assert_eq!(Some(&3), iter.next()); + /// + /// // ... and then None once it's over. + /// assert_eq!(None, iter.next()); + /// + /// // More calls may or may not return None. Here, they always will. + /// assert_eq!(None, iter.next()); + /// assert_eq!(None, iter.next()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + fn next(&mut self) -> Option<Self::Item>; + + /// Returns the bounds on the remaining length of the iterator. + /// + /// Specifically, `size_hint()` returns a tuple where the first element + /// is the lower bound, and the second element is the upper bound. + /// + /// The second half of the tuple that is returned is an `Option<usize>`. A + /// `None` here means that either there is no known upper bound, or the + /// upper bound is larger than `usize`. + /// + /// # Implementation notes + /// + /// It is not enforced that an iterator implementation yields the declared + /// number of elements. A buggy iterator may yield less than the lower bound + /// or more than the upper bound of elements. + /// + /// `size_hint()` is primarily intended to be used for optimizations such as + /// reserving space for the elements of the iterator, but must not be + /// trusted to e.g. omit bounds checks in unsafe code. An incorrect + /// implementation of `size_hint()` should not lead to memory safety + /// violations. + /// + /// That said, the implementation should provide a correct estimation, + /// because otherwise it would be a violation of the trait's protocol. + /// + /// The default implementation returns `(0, None)` which is correct for any + /// iterator. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// let iter = a.iter(); + /// + /// assert_eq!((3, Some(3)), iter.size_hint()); + /// ``` + /// + /// A more complex example: + /// + /// ``` + /// // The even numbers from zero to ten. + /// let iter = (0..10).filter(|x| x % 2 == 0); + /// + /// // We might iterate from zero to ten times. Knowing that it's five + /// // exactly wouldn't be possible without executing filter(). + /// assert_eq!((0, Some(10)), iter.size_hint()); + /// + /// // Let's add one five more numbers with chain() + /// let iter = (0..10).filter(|x| x % 2 == 0).chain(15..20); + /// + /// // now both bounds are increased by five + /// assert_eq!((5, Some(15)), iter.size_hint()); + /// ``` + /// + /// Returning `None` for an upper bound: + /// + /// ``` + /// // an infinite iterator has no upper bound + /// let iter = 0..; + /// + /// assert_eq!((0, None), iter.size_hint()); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn size_hint(&self) -> (usize, Option<usize>) { (0, None) } + + /// Consumes the iterator, counting the number of iterations and returning it. + /// + /// This method will evaluate the iterator until its [`next()`] returns + /// `None`. Once `None` is encountered, `count()` returns the number of + /// times it called [`next()`]. + /// + /// [`next()`]: #tymethod.next + /// + /// # Overflow Behavior + /// + /// The method does no guarding against overflows, so counting elements of + /// an iterator with more than `usize::MAX` elements either produces the + /// wrong result or panics. If debug assertions are enabled, a panic is + /// guaranteed. + /// + /// # Panics + /// + /// This function might panic if the iterator has more than `usize::MAX` + /// elements. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// assert_eq!(a.iter().count(), 3); + /// + /// let a = [1, 2, 3, 4, 5]; + /// assert_eq!(a.iter().count(), 5); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn count(self) -> usize where Self: Sized { + // Might overflow. + self.fold(0, |cnt, _| cnt + 1) + } + + /// Consumes the iterator, returning the last element. + /// + /// This method will evaluate the iterator until it returns `None`. While + /// doing so, it keeps track of the current element. After `None` is + /// returned, `last()` will then return the last element it saw. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// assert_eq!(a.iter().last(), Some(&3)); + /// + /// let a = [1, 2, 3, 4, 5]; + /// assert_eq!(a.iter().last(), Some(&5)); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn last(self) -> Option<Self::Item> where Self: Sized { + let mut last = None; + for x in self { last = Some(x); } + last + } + + /// Consumes the `n` first elements of the iterator, then returns the + /// `next()` one. + /// + /// This method will evaluate the iterator `n` times, discarding those elements. + /// After it does so, it will call [`next()`] and return its value. + /// + /// [`next()`]: #tymethod.next + /// + /// Like most indexing operations, the count starts from zero, so `nth(0)` + /// returns the first value, `nth(1)` the second, and so on. + /// + /// `nth()` will return `None` if `n` is larger than the length of the + /// iterator. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// assert_eq!(a.iter().nth(1), Some(&2)); + /// ``` + /// + /// Calling `nth()` multiple times doesn't rewind the iterator: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.iter(); + /// + /// assert_eq!(iter.nth(1), Some(&2)); + /// assert_eq!(iter.nth(1), None); + /// ``` + /// + /// Returning `None` if there are less than `n` elements: + /// + /// ``` + /// let a = [1, 2, 3]; + /// assert_eq!(a.iter().nth(10), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn nth(&mut self, mut n: usize) -> Option<Self::Item> where Self: Sized { + for x in self { + if n == 0 { return Some(x) } + n -= 1; + } + None + } + + /// Takes two iterators and creates a new iterator over both in sequence. + /// + /// `chain()` will return a new iterator which will first iterate over + /// values from the first iterator and then over values from the second + /// iterator. + /// + /// In other words, it links two iterators together, in a chain. 🔗 + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a1 = [1, 2, 3]; + /// let a2 = [4, 5, 6]; + /// + /// let mut iter = a1.iter().chain(a2.iter()); + /// + /// assert_eq!(iter.next(), Some(&1)); + /// assert_eq!(iter.next(), Some(&2)); + /// assert_eq!(iter.next(), Some(&3)); + /// assert_eq!(iter.next(), Some(&4)); + /// assert_eq!(iter.next(), Some(&5)); + /// assert_eq!(iter.next(), Some(&6)); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// Since the argument to `chain()` uses [`IntoIterator`], we can pass + /// anything that can be converted into an [`Iterator`], not just an + /// [`Iterator`] itself. For example, slices (`&[T]`) implement + /// [`IntoIterator`], and so can be passed to `chain()` directly: + /// + /// [`IntoIterator`]: trait.IntoIterator.html + /// [`Iterator`]: trait.Iterator.html + /// + /// ``` + /// let s1 = &[1, 2, 3]; + /// let s2 = &[4, 5, 6]; + /// + /// let mut iter = s1.iter().chain(s2); + /// + /// assert_eq!(iter.next(), Some(&1)); + /// assert_eq!(iter.next(), Some(&2)); + /// assert_eq!(iter.next(), Some(&3)); + /// assert_eq!(iter.next(), Some(&4)); + /// assert_eq!(iter.next(), Some(&5)); + /// assert_eq!(iter.next(), Some(&6)); + /// assert_eq!(iter.next(), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> where + Self: Sized, U: IntoIterator<Item=Self::Item>, + { + Chain{a: self, b: other.into_iter(), state: ChainState::Both} + } + + /// 'Zips up' two iterators into a single iterator of pairs. + /// + /// `zip()` returns a new iterator that will iterate over two other + /// iterators, returning a tuple where the first element comes from the + /// first iterator, and the second element comes from the second iterator. + /// + /// In other words, it zips two iterators together, into a single one. + /// + /// When either iterator returns `None`, all further calls to `next()` + /// will return `None`. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a1 = [1, 2, 3]; + /// let a2 = [4, 5, 6]; + /// + /// let mut iter = a1.iter().zip(a2.iter()); + /// + /// assert_eq!(iter.next(), Some((&1, &4))); + /// assert_eq!(iter.next(), Some((&2, &5))); + /// assert_eq!(iter.next(), Some((&3, &6))); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// Since the argument to `zip()` uses [`IntoIterator`], we can pass + /// anything that can be converted into an [`Iterator`], not just an + /// [`Iterator`] itself. For example, slices (`&[T]`) implement + /// [`IntoIterator`], and so can be passed to `zip()` directly: + /// + /// [`IntoIterator`]: trait.IntoIterator.html + /// [`Iterator`]: trait.Iterator.html + /// + /// ``` + /// let s1 = &[1, 2, 3]; + /// let s2 = &[4, 5, 6]; + /// + /// let mut iter = s1.iter().zip(s2); + /// + /// assert_eq!(iter.next(), Some((&1, &4))); + /// assert_eq!(iter.next(), Some((&2, &5))); + /// assert_eq!(iter.next(), Some((&3, &6))); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// `zip()` is often used to zip an infinite iterator to a finite one. + /// This works because the finite iterator will eventually return `None`, + /// ending the zipper. Zipping with `(0..)` can look a lot like [`enumerate()`]: + /// + /// ``` + /// let enumerate: Vec<_> = "foo".chars().enumerate().collect(); + /// + /// let zipper: Vec<_> = (0..).zip("foo".chars()).collect(); + /// + /// assert_eq!((0, 'f'), enumerate[0]); + /// assert_eq!((0, 'f'), zipper[0]); + /// + /// assert_eq!((1, 'o'), enumerate[1]); + /// assert_eq!((1, 'o'), zipper[1]); + /// + /// assert_eq!((2, 'o'), enumerate[2]); + /// assert_eq!((2, 'o'), zipper[2]); + /// ``` + /// + /// [`enumerate()`]: trait.Iterator.html#method.enumerate + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> where + Self: Sized, U: IntoIterator + { + Zip{a: self, b: other.into_iter()} + } + + /// Takes a closure and creates an iterator which calls that closure on each + /// element. + /// + /// `map()` transforms one iterator into another, by means of its argument: + /// something that implements `FnMut`. It produces a new iterator which + /// calls this closure on each element of the original iterator. + /// + /// If you are good at thinking in types, you can think of `map()` like this: + /// If you have an iterator that gives you elements of some type `A`, and + /// you want an iterator of some other type `B`, you can use `map()`, + /// passing a closure that takes an `A` and returns a `B`. + /// + /// `map()` is conceptually similar to a [`for`] loop. However, as `map()` is + /// lazy, it is best used when you're already working with other iterators. + /// If you're doing some sort of looping for a side effect, it's considered + /// more idiomatic to use [`for`] than `map()`. + /// + /// [`for`]: ../../book/loops.html#for + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.into_iter().map(|x| 2 * x); + /// + /// assert_eq!(iter.next(), Some(2)); + /// assert_eq!(iter.next(), Some(4)); + /// assert_eq!(iter.next(), Some(6)); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// If you're doing some sort of side effect, prefer [`for`] to `map()`: + /// + /// ``` + /// # #![allow(unused_must_use)] + /// // don't do this: + /// (0..5).map(|x| println!("{}", x)); + /// + /// // it won't even execute, as it is lazy. Rust will warn you about this. + /// + /// // Instead, use for: + /// for x in 0..5 { + /// println!("{}", x); + /// } + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn map<B, F>(self, f: F) -> Map<Self, F> where + Self: Sized, F: FnMut(Self::Item) -> B, + { + Map{iter: self, f: f} + } + + /// Creates an iterator which uses a closure to determine if an element + /// should be yielded. + /// + /// The closure must return `true` or `false`. `filter()` creates an + /// iterator which calls this closure on each element. If the closure + /// returns `true`, then the element is returned. If the closure returns + /// `false`, it will try again, and call the closure on the next element, + /// seeing if it passes the test. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [0i32, 1, 2]; + /// + /// let mut iter = a.into_iter().filter(|x| x.is_positive()); + /// + /// assert_eq!(iter.next(), Some(&1)); + /// assert_eq!(iter.next(), Some(&2)); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// Because the closure passed to `filter()` takes a reference, and many + /// iterators iterate over references, this leads to a possibly confusing + /// situation, where the type of the closure is a double reference: + /// + /// ``` + /// let a = [0, 1, 2]; + /// + /// let mut iter = a.into_iter().filter(|x| **x > 1); // need two *s! + /// + /// assert_eq!(iter.next(), Some(&2)); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// It's common to instead use destructuring on the argument to strip away + /// one: + /// + /// ``` + /// let a = [0, 1, 2]; + /// + /// let mut iter = a.into_iter().filter(|&x| *x > 1); // both & and * + /// + /// assert_eq!(iter.next(), Some(&2)); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// or both: + /// + /// ``` + /// let a = [0, 1, 2]; + /// + /// let mut iter = a.into_iter().filter(|&&x| x > 1); // two &s + /// + /// assert_eq!(iter.next(), Some(&2)); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// of these layers. + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn filter<P>(self, predicate: P) -> Filter<Self, P> where + Self: Sized, P: FnMut(&Self::Item) -> bool, + { + Filter{iter: self, predicate: predicate} + } + + /// Creates an iterator that both filters and maps. + /// + /// The closure must return an [`Option<T>`]. `filter_map()` creates an + /// iterator which calls this closure on each element. If the closure + /// returns `Some(element)`, then that element is returned. If the + /// closure returns `None`, it will try again, and call the closure on the + /// next element, seeing if it will return `Some`. + /// + /// [`Option<T>`]: ../../std/option/enum.Option.html + /// + /// Why `filter_map()` and not just [`filter()`].[`map()`]? The key is in this + /// part: + /// + /// [`filter()`]: #method.filter + /// [`map()`]: #method.map + /// + /// > If the closure returns `Some(element)`, then that element is returned. + /// + /// In other words, it removes the [`Option<T>`] layer automatically. If your + /// mapping is already returning an [`Option<T>`] and you want to skip over + /// `None`s, then `filter_map()` is much, much nicer to use. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = ["1", "2", "lol"]; + /// + /// let mut iter = a.iter().filter_map(|s| s.parse().ok()); + /// + /// assert_eq!(iter.next(), Some(1)); + /// assert_eq!(iter.next(), Some(2)); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// Here's the same example, but with [`filter()`] and [`map()`]: + /// + /// ``` + /// let a = ["1", "2", "lol"]; + /// + /// let mut iter = a.iter() + /// .map(|s| s.parse().ok()) + /// .filter(|s| s.is_some()); + /// + /// assert_eq!(iter.next(), Some(Some(1))); + /// assert_eq!(iter.next(), Some(Some(2))); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// There's an extra layer of `Some` in there. + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where + Self: Sized, F: FnMut(Self::Item) -> Option<B>, + { + FilterMap { iter: self, f: f } + } + + /// Creates an iterator which gives the current iteration count as well as + /// the next value. + /// + /// The iterator returned yields pairs `(i, val)`, where `i` is the + /// current index of iteration and `val` is the value returned by the + /// iterator. + /// + /// `enumerate()` keeps its count as a [`usize`]. If you want to count by a + /// different sized integer, the [`zip()`] function provides similar + /// functionality. + /// + /// [`usize`]: ../../std/primitive.usize.html + /// [`zip()`]: #method.zip + /// + /// # Overflow Behavior + /// + /// The method does no guarding against overflows, so enumerating more than + /// [`usize::MAX`] elements either produces the wrong result or panics. If + /// debug assertions are enabled, a panic is guaranteed. + /// + /// [`usize::MAX`]: ../../std/usize/constant.MAX.html + /// + /// # Panics + /// + /// The returned iterator might panic if the to-be-returned index would + /// overflow a `usize`. + /// + /// # Examples + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.iter().enumerate(); + /// + /// assert_eq!(iter.next(), Some((0, &1))); + /// assert_eq!(iter.next(), Some((1, &2))); + /// assert_eq!(iter.next(), Some((2, &3))); + /// assert_eq!(iter.next(), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn enumerate(self) -> Enumerate<Self> where Self: Sized { + Enumerate { iter: self, count: 0 } + } + + /// Creates an iterator which can use `peek` to look at the next element of + /// the iterator without consuming it. + /// + /// Adds a [`peek()`] method to an iterator. See its documentation for + /// more information. + /// + /// Note that the underlying iterator is still advanced when `peek` is + /// called for the first time: In order to retrieve the next element, + /// `next` is called on the underlying iterator, hence any side effects of + /// the `next` method will occur. + /// + /// [`peek()`]: struct.Peekable.html#method.peek + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let xs = [1, 2, 3]; + /// + /// let mut iter = xs.iter().peekable(); + /// + /// // peek() lets us see into the future + /// assert_eq!(iter.peek(), Some(&&1)); + /// assert_eq!(iter.next(), Some(&1)); + /// + /// assert_eq!(iter.next(), Some(&2)); + /// + /// // we can peek() multiple times, the iterator won't advance + /// assert_eq!(iter.peek(), Some(&&3)); + /// assert_eq!(iter.peek(), Some(&&3)); + /// + /// assert_eq!(iter.next(), Some(&3)); + /// + /// // after the iterator is finished, so is peek() + /// assert_eq!(iter.peek(), None); + /// assert_eq!(iter.next(), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn peekable(self) -> Peekable<Self> where Self: Sized { + Peekable{iter: self, peeked: None} + } + + /// Creates an iterator that [`skip()`]s elements based on a predicate. + /// + /// [`skip()`]: #method.skip + /// + /// `skip_while()` takes a closure as an argument. It will call this + /// closure on each element of the iterator, and ignore elements + /// until it returns `false`. + /// + /// After `false` is returned, `skip_while()`'s job is over, and the + /// rest of the elements are yielded. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [-1i32, 0, 1]; + /// + /// let mut iter = a.into_iter().skip_while(|x| x.is_negative()); + /// + /// assert_eq!(iter.next(), Some(&0)); + /// assert_eq!(iter.next(), Some(&1)); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// Because the closure passed to `skip_while()` takes a reference, and many + /// iterators iterate over references, this leads to a possibly confusing + /// situation, where the type of the closure is a double reference: + /// + /// ``` + /// let a = [-1, 0, 1]; + /// + /// let mut iter = a.into_iter().skip_while(|x| **x < 0); // need two *s! + /// + /// assert_eq!(iter.next(), Some(&0)); + /// assert_eq!(iter.next(), Some(&1)); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// Stopping after an initial `false`: + /// + /// ``` + /// let a = [-1, 0, 1, -2]; + /// + /// let mut iter = a.into_iter().skip_while(|x| **x < 0); + /// + /// assert_eq!(iter.next(), Some(&0)); + /// assert_eq!(iter.next(), Some(&1)); + /// + /// // while this would have been false, since we already got a false, + /// // skip_while() isn't used any more + /// assert_eq!(iter.next(), Some(&-2)); + /// + /// assert_eq!(iter.next(), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where + Self: Sized, P: FnMut(&Self::Item) -> bool, + { + SkipWhile{iter: self, flag: false, predicate: predicate} + } + + /// Creates an iterator that yields elements based on a predicate. + /// + /// `take_while()` takes a closure as an argument. It will call this + /// closure on each element of the iterator, and yield elements + /// while it returns `true`. + /// + /// After `false` is returned, `take_while()`'s job is over, and the + /// rest of the elements are ignored. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [-1i32, 0, 1]; + /// + /// let mut iter = a.into_iter().take_while(|x| x.is_negative()); + /// + /// assert_eq!(iter.next(), Some(&-1)); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// Because the closure passed to `take_while()` takes a reference, and many + /// iterators iterate over references, this leads to a possibly confusing + /// situation, where the type of the closure is a double reference: + /// + /// ``` + /// let a = [-1, 0, 1]; + /// + /// let mut iter = a.into_iter().take_while(|x| **x < 0); // need two *s! + /// + /// assert_eq!(iter.next(), Some(&-1)); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// Stopping after an initial `false`: + /// + /// ``` + /// let a = [-1, 0, 1, -2]; + /// + /// let mut iter = a.into_iter().take_while(|x| **x < 0); + /// + /// assert_eq!(iter.next(), Some(&-1)); + /// + /// // We have more elements that are less than zero, but since we already + /// // got a false, take_while() isn't used any more + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// Because `take_while()` needs to look at the value in order to see if it + /// should be included or not, consuming iterators will see that it is + /// removed: + /// + /// ``` + /// let a = [1, 2, 3, 4]; + /// let mut iter = a.into_iter(); + /// + /// let result: Vec<i32> = iter.by_ref() + /// .take_while(|n| **n != 3) + /// .cloned() + /// .collect(); + /// + /// assert_eq!(result, &[1, 2]); + /// + /// let result: Vec<i32> = iter.cloned().collect(); + /// + /// assert_eq!(result, &[4]); + /// ``` + /// + /// The `3` is no longer there, because it was consumed in order to see if + /// the iteration should stop, but wasn't placed back into the iterator or + /// some similar thing. + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where + Self: Sized, P: FnMut(&Self::Item) -> bool, + { + TakeWhile{iter: self, flag: false, predicate: predicate} + } + + /// Creates an iterator that skips the first `n` elements. + /// + /// After they have been consumed, the rest of the elements are yielded. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.iter().skip(2); + /// + /// assert_eq!(iter.next(), Some(&3)); + /// assert_eq!(iter.next(), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn skip(self, n: usize) -> Skip<Self> where Self: Sized { + Skip{iter: self, n: n} + } + + /// Creates an iterator that yields its first `n` elements. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.iter().take(2); + /// + /// assert_eq!(iter.next(), Some(&1)); + /// assert_eq!(iter.next(), Some(&2)); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// `take()` is often used with an infinite iterator, to make it finite: + /// + /// ``` + /// let mut iter = (0..).take(3); + /// + /// assert_eq!(iter.next(), Some(0)); + /// assert_eq!(iter.next(), Some(1)); + /// assert_eq!(iter.next(), Some(2)); + /// assert_eq!(iter.next(), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn take(self, n: usize) -> Take<Self> where Self: Sized, { + Take{iter: self, n: n} + } + + /// An iterator adaptor similar to [`fold()`] that holds internal state and + /// produces a new iterator. + /// + /// [`fold()`]: #method.fold + /// + /// `scan()` takes two arguments: an initial value which seeds the internal + /// state, and a closure with two arguments, the first being a mutable + /// reference to the internal state and the second an iterator element. + /// The closure can assign to the internal state to share state between + /// iterations. + /// + /// On iteration, the closure will be applied to each element of the + /// iterator and the return value from the closure, an [`Option`], is + /// yielded by the iterator. + /// + /// [`Option`]: ../../std/option/enum.Option.html + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.iter().scan(1, |state, &x| { + /// // each iteration, we'll multiply the state by the element + /// *state = *state * x; + /// + /// // the value passed on to the next iteration + /// Some(*state) + /// }); + /// + /// assert_eq!(iter.next(), Some(1)); + /// assert_eq!(iter.next(), Some(2)); + /// assert_eq!(iter.next(), Some(6)); + /// assert_eq!(iter.next(), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> + where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option<B>, + { + Scan{iter: self, f: f, state: initial_state} + } + + /// Creates an iterator that works like map, but flattens nested structure. + /// + /// The [`map()`] adapter is very useful, but only when the closure + /// argument produces values. If it produces an iterator instead, there's + /// an extra layer of indirection. `flat_map()` will remove this extra layer + /// on its own. + /// + /// [`map()`]: #method.map + /// + /// Another way of thinking about `flat_map()`: [`map()`]'s closure returns + /// one item for each element, and `flat_map()`'s closure returns an + /// iterator for each element. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let words = ["alpha", "beta", "gamma"]; + /// + /// // chars() returns an iterator + /// let merged: String = words.iter() + /// .flat_map(|s| s.chars()) + /// .collect(); + /// assert_eq!(merged, "alphabetagamma"); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> + where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U, + { + FlatMap{iter: self, f: f, frontiter: None, backiter: None } + } + + /// Creates an iterator which ends after the first `None`. + /// + /// After an iterator returns `None`, future calls may or may not yield + /// `Some(T)` again. `fuse()` adapts an iterator, ensuring that after a + /// `None` is given, it will always return `None` forever. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// // an iterator which alternates between Some and None + /// struct Alternate { + /// state: i32, + /// } + /// + /// impl Iterator for Alternate { + /// type Item = i32; + /// + /// fn next(&mut self) -> Option<i32> { + /// let val = self.state; + /// self.state = self.state + 1; + /// + /// // if it's even, Some(i32), else None + /// if val % 2 == 0 { + /// Some(val) + /// } else { + /// None + /// } + /// } + /// } + /// + /// let mut iter = Alternate { state: 0 }; + /// + /// // we can see our iterator going back and forth + /// assert_eq!(iter.next(), Some(0)); + /// assert_eq!(iter.next(), None); + /// assert_eq!(iter.next(), Some(2)); + /// assert_eq!(iter.next(), None); + /// + /// // however, once we fuse it... + /// let mut iter = iter.fuse(); + /// + /// assert_eq!(iter.next(), Some(4)); + /// assert_eq!(iter.next(), None); + /// + /// // it will always return None after the first time. + /// assert_eq!(iter.next(), None); + /// assert_eq!(iter.next(), None); + /// assert_eq!(iter.next(), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn fuse(self) -> Fuse<Self> where Self: Sized { + Fuse{iter: self, done: false} + } + + /// Do something with each element of an iterator, passing the value on. + /// + /// When using iterators, you'll often chain several of them together. + /// While working on such code, you might want to check out what's + /// happening at various parts in the pipeline. To do that, insert + /// a call to `inspect()`. + /// + /// It's much more common for `inspect()` to be used as a debugging tool + /// than to exist in your final code, but never say never. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 4, 2, 3]; + /// + /// // this iterator sequence is complex. + /// let sum = a.iter() + /// .cloned() + /// .filter(|&x| x % 2 == 0) + /// .fold(0, |sum, i| sum + i); + /// + /// println!("{}", sum); + /// + /// // let's add some inspect() calls to investigate what's happening + /// let sum = a.iter() + /// .cloned() + /// .inspect(|x| println!("about to filter: {}", x)) + /// .filter(|&x| x % 2 == 0) + /// .inspect(|x| println!("made it through filter: {}", x)) + /// .fold(0, |sum, i| sum + i); + /// + /// println!("{}", sum); + /// ``` + /// + /// This will print: + /// + /// ```text + /// about to filter: 1 + /// about to filter: 4 + /// made it through filter: 4 + /// about to filter: 2 + /// made it through filter: 2 + /// about to filter: 3 + /// 6 + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn inspect<F>(self, f: F) -> Inspect<Self, F> where + Self: Sized, F: FnMut(&Self::Item), + { + Inspect{iter: self, f: f} + } + + /// Borrows an iterator, rather than consuming it. + /// + /// This is useful to allow applying iterator adaptors while still + /// retaining ownership of the original iterator. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let iter = a.into_iter(); + /// + /// let sum: i32 = iter.take(5) + /// .fold(0, |acc, &i| acc + i ); + /// + /// assert_eq!(sum, 6); + /// + /// // if we try to use iter again, it won't work. The following line + /// // gives "error: use of moved value: `iter` + /// // assert_eq!(iter.next(), None); + /// + /// // let's try that again + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.into_iter(); + /// + /// // instead, we add in a .by_ref() + /// let sum: i32 = iter.by_ref() + /// .take(2) + /// .fold(0, |acc, &i| acc + i ); + /// + /// assert_eq!(sum, 3); + /// + /// // now this is just fine: + /// assert_eq!(iter.next(), Some(&3)); + /// assert_eq!(iter.next(), None); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + fn by_ref(&mut self) -> &mut Self where Self: Sized { self } + + /// Transforms an iterator into a collection. + /// + /// `collect()` can take anything iterable, and turn it into a relevant + /// collection. This is one of the more powerful methods in the standard + /// library, used in a variety of contexts. + /// + /// The most basic pattern in which `collect()` is used is to turn one + /// collection into another. You take a collection, call `iter()` on it, + /// do a bunch of transformations, and then `collect()` at the end. + /// + /// One of the keys to `collect()`'s power is that many things you might + /// not think of as 'collections' actually are. For example, a [`String`] + /// is a collection of [`char`]s. And a collection of [`Result<T, E>`] can + /// be thought of as single `Result<Collection<T>, E>`. See the examples + /// below for more. + /// + /// [`String`]: ../../std/string/struct.String.html + /// [`Result<T, E>`]: ../../std/result/enum.Result.html + /// [`char`]: ../../std/primitive.char.html + /// + /// Because `collect()` is so general, it can cause problems with type + /// inference. As such, `collect()` is one of the few times you'll see + /// the syntax affectionately known as the 'turbofish': `::<>`. This + /// helps the inference algorithm understand specifically which collection + /// you're trying to collect into. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let doubled: Vec<i32> = a.iter() + /// .map(|&x| x * 2) + /// .collect(); + /// + /// assert_eq!(vec![2, 4, 6], doubled); + /// ``` + /// + /// Note that we needed the `: Vec<i32>` on the left-hand side. This is because + /// we could collect into, for example, a [`VecDeque<T>`] instead: + /// + /// [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let a = [1, 2, 3]; + /// + /// let doubled: VecDeque<i32> = a.iter() + /// .map(|&x| x * 2) + /// .collect(); + /// + /// assert_eq!(2, doubled[0]); + /// assert_eq!(4, doubled[1]); + /// assert_eq!(6, doubled[2]); + /// ``` + /// + /// Using the 'turbofish' instead of annotating `doubled`: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let doubled = a.iter() + /// .map(|&x| x * 2) + /// .collect::<Vec<i32>>(); + /// + /// assert_eq!(vec![2, 4, 6], doubled); + /// ``` + /// + /// Because `collect()` cares about what you're collecting into, you can + /// still use a partial type hint, `_`, with the turbofish: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let doubled = a.iter() + /// .map(|&x| x * 2) + /// .collect::<Vec<_>>(); + /// + /// assert_eq!(vec![2, 4, 6], doubled); + /// ``` + /// + /// Using `collect()` to make a [`String`]: + /// + /// ``` + /// let chars = ['g', 'd', 'k', 'k', 'n']; + /// + /// let hello: String = chars.iter() + /// .map(|&x| x as u8) + /// .map(|x| (x + 1) as char) + /// .collect(); + /// + /// assert_eq!("hello", hello); + /// ``` + /// + /// If you have a list of [`Result<T, E>`]s, you can use `collect()` to + /// see if any of them failed: + /// + /// ``` + /// let results = [Ok(1), Err("nope"), Ok(3), Err("bad")]; + /// + /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect(); + /// + /// // gives us the first error + /// assert_eq!(Err("nope"), result); + /// + /// let results = [Ok(1), Ok(3)]; + /// + /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect(); + /// + /// // gives us the list of answers + /// assert_eq!(Ok(vec![1, 3]), result); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn collect<B: FromIterator<Self::Item>>(self) -> B where Self: Sized { + FromIterator::from_iter(self) + } + + /// Consumes an iterator, creating two collections from it. + /// + /// The predicate passed to `partition()` can return `true`, or `false`. + /// `partition()` returns a pair, all of the elements for which it returned + /// `true`, and all of the elements for which it returned `false`. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let (even, odd): (Vec<i32>, Vec<i32>) = a.into_iter() + /// .partition(|&n| n % 2 == 0); + /// + /// assert_eq!(even, vec![2]); + /// assert_eq!(odd, vec![1, 3]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + fn partition<B, F>(self, mut f: F) -> (B, B) where + Self: Sized, + B: Default + Extend<Self::Item>, + F: FnMut(&Self::Item) -> bool + { + let mut left: B = Default::default(); + let mut right: B = Default::default(); + + for x in self { + if f(&x) { + left.extend(Some(x)) + } else { + right.extend(Some(x)) + } + } + + (left, right) + } + + /// An iterator adaptor that applies a function, producing a single, final value. + /// + /// `fold()` takes two arguments: an initial value, and a closure with two + /// arguments: an 'accumulator', and an element. The closure returns the value that + /// the accumulator should have for the next iteration. + /// + /// The initial value is the value the accumulator will have on the first + /// call. + /// + /// After applying this closure to every element of the iterator, `fold()` + /// returns the accumulator. + /// + /// This operation is sometimes called 'reduce' or 'inject'. + /// + /// Folding is useful whenever you have a collection of something, and want + /// to produce a single value from it. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// // the sum of all of the elements of a + /// let sum = a.iter() + /// .fold(0, |acc, &x| acc + x); + /// + /// assert_eq!(sum, 6); + /// ``` + /// + /// Let's walk through each step of the iteration here: + /// + /// | element | acc | x | result | + /// |---------|-----|---|--------| + /// | | 0 | | | + /// | 1 | 0 | 1 | 1 | + /// | 2 | 1 | 2 | 3 | + /// | 3 | 3 | 3 | 6 | + /// + /// And so, our final result, `6`. + /// + /// It's common for people who haven't used iterators a lot to + /// use a `for` loop with a list of things to build up a result. Those + /// can be turned into `fold()`s: + /// + /// ``` + /// let numbers = [1, 2, 3, 4, 5]; + /// + /// let mut result = 0; + /// + /// // for loop: + /// for i in &numbers { + /// result = result + i; + /// } + /// + /// // fold: + /// let result2 = numbers.iter().fold(0, |acc, &x| acc + x); + /// + /// // they're the same + /// assert_eq!(result, result2); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn fold<B, F>(self, init: B, mut f: F) -> B where + Self: Sized, F: FnMut(B, Self::Item) -> B, + { + let mut accum = init; + for x in self { + accum = f(accum, x); + } + accum + } + + /// Tests if every element of the iterator matches a predicate. + /// + /// `all()` takes a closure that returns `true` or `false`. It applies + /// this closure to each element of the iterator, and if they all return + /// `true`, then so does `all()`. If any of them return `false`, it + /// returns `false`. + /// + /// `all()` is short-circuiting; in other words, it will stop processing + /// as soon as it finds a `false`, given that no matter what else happens, + /// the result will also be `false`. + /// + /// An empty iterator returns `true`. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// assert!(a.iter().all(|&x| x > 0)); + /// + /// assert!(!a.iter().all(|&x| x > 2)); + /// ``` + /// + /// Stopping at the first `false`: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.iter(); + /// + /// assert!(!iter.all(|&x| x != 2)); + /// + /// // we can still use `iter`, as there are more elements. + /// assert_eq!(iter.next(), Some(&3)); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn all<F>(&mut self, mut f: F) -> bool where + Self: Sized, F: FnMut(Self::Item) -> bool + { + for x in self { + if !f(x) { + return false; + } + } + true + } + + /// Tests if any element of the iterator matches a predicate. + /// + /// `any()` takes a closure that returns `true` or `false`. It applies + /// this closure to each element of the iterator, and if any of them return + /// `true`, then so does `any()`. If they all return `false`, it + /// returns `false`. + /// + /// `any()` is short-circuiting; in other words, it will stop processing + /// as soon as it finds a `true`, given that no matter what else happens, + /// the result will also be `true`. + /// + /// An empty iterator returns `false`. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// assert!(a.iter().any(|&x| x > 0)); + /// + /// assert!(!a.iter().any(|&x| x > 5)); + /// ``` + /// + /// Stopping at the first `true`: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.iter(); + /// + /// assert!(iter.any(|&x| x != 2)); + /// + /// // we can still use `iter`, as there are more elements. + /// assert_eq!(iter.next(), Some(&2)); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn any<F>(&mut self, mut f: F) -> bool where + Self: Sized, + F: FnMut(Self::Item) -> bool + { + for x in self { + if f(x) { + return true; + } + } + false + } + + /// Searches for an element of an iterator that satisfies a predicate. + /// + /// `find()` takes a closure that returns `true` or `false`. It applies + /// this closure to each element of the iterator, and if any of them return + /// `true`, then `find()` returns `Some(element)`. If they all return + /// `false`, it returns `None`. + /// + /// `find()` is short-circuiting; in other words, it will stop processing + /// as soon as the closure returns `true`. + /// + /// Because `find()` takes a reference, and many iterators iterate over + /// references, this leads to a possibly confusing situation where the + /// argument is a double reference. You can see this effect in the + /// examples below, with `&&x`. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// assert_eq!(a.iter().find(|&&x| x == 2), Some(&2)); + /// + /// assert_eq!(a.iter().find(|&&x| x == 5), None); + /// ``` + /// + /// Stopping at the first `true`: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.iter(); + /// + /// assert_eq!(iter.find(|&&x| x == 2), Some(&2)); + /// + /// // we can still use `iter`, as there are more elements. + /// assert_eq!(iter.next(), Some(&3)); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn find<P>(&mut self, mut predicate: P) -> Option<Self::Item> where + Self: Sized, + P: FnMut(&Self::Item) -> bool, + { + for x in self { + if predicate(&x) { return Some(x) } + } + None + } + + /// Searches for an element in an iterator, returning its index. + /// + /// `position()` takes a closure that returns `true` or `false`. It applies + /// this closure to each element of the iterator, and if one of them + /// returns `true`, then `position()` returns `Some(index)`. If all of + /// them return `false`, it returns `None`. + /// + /// `position()` is short-circuiting; in other words, it will stop + /// processing as soon as it finds a `true`. + /// + /// # Overflow Behavior + /// + /// The method does no guarding against overflows, so if there are more + /// than `usize::MAX` non-matching elements, it either produces the wrong + /// result or panics. If debug assertions are enabled, a panic is + /// guaranteed. + /// + /// # Panics + /// + /// This function might panic if the iterator has more than `usize::MAX` + /// non-matching elements. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// assert_eq!(a.iter().position(|&x| x == 2), Some(1)); + /// + /// assert_eq!(a.iter().position(|&x| x == 5), None); + /// ``` + /// + /// Stopping at the first `true`: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.iter(); + /// + /// assert_eq!(iter.position(|&x| x == 2), Some(1)); + /// + /// // we can still use `iter`, as there are more elements. + /// assert_eq!(iter.next(), Some(&3)); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn position<P>(&mut self, mut predicate: P) -> Option<usize> where + Self: Sized, + P: FnMut(Self::Item) -> bool, + { + // `enumerate` might overflow. + for (i, x) in self.enumerate() { + if predicate(x) { + return Some(i); + } + } + None + } + + /// Searches for an element in an iterator from the right, returning its + /// index. + /// + /// `rposition()` takes a closure that returns `true` or `false`. It applies + /// this closure to each element of the iterator, starting from the end, + /// and if one of them returns `true`, then `rposition()` returns + /// `Some(index)`. If all of them return `false`, it returns `None`. + /// + /// `rposition()` is short-circuiting; in other words, it will stop + /// processing as soon as it finds a `true`. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// assert_eq!(a.iter().rposition(|&x| x == 3), Some(2)); + /// + /// assert_eq!(a.iter().rposition(|&x| x == 5), None); + /// ``` + /// + /// Stopping at the first `true`: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.iter(); + /// + /// assert_eq!(iter.rposition(|&x| x == 2), Some(1)); + /// + /// // we can still use `iter`, as there are more elements. + /// assert_eq!(iter.next(), Some(&1)); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn rposition<P>(&mut self, mut predicate: P) -> Option<usize> where + P: FnMut(Self::Item) -> bool, + Self: Sized + ExactSizeIterator + DoubleEndedIterator + { + let mut i = self.len(); + + while let Some(v) = self.next_back() { + if predicate(v) { + return Some(i - 1); + } + // No need for an overflow check here, because `ExactSizeIterator` + // implies that the number of elements fits into a `usize`. + i -= 1; + } + None + } + + /// Returns the maximum element of an iterator. + /// + /// If the two elements are equally maximum, the latest element is + /// returned. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// assert_eq!(a.iter().max(), Some(&3)); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn max(self) -> Option<Self::Item> where Self: Sized, Self::Item: Ord + { + select_fold1(self, + |_| (), + // switch to y even if it is only equal, to preserve + // stability. + |_, x, _, y| *x <= *y) + .map(|(_, x)| x) + } + + /// Returns the minimum element of an iterator. + /// + /// If the two elements are equally minimum, the first element is + /// returned. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// assert_eq!(a.iter().min(), Some(&1)); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn min(self) -> Option<Self::Item> where Self: Sized, Self::Item: Ord + { + select_fold1(self, + |_| (), + // only switch to y if it is strictly smaller, to + // preserve stability. + |_, x, _, y| *x > *y) + .map(|(_, x)| x) + } + + /// Returns the element that gives the maximum value from the + /// specified function. + /// + /// Returns the rightmost element if the comparison determines two elements + /// to be equally maximum. + /// + /// # Examples + /// + /// ``` + /// let a = [-3_i32, 0, 1, 5, -10]; + /// assert_eq!(*a.iter().max_by_key(|x| x.abs()).unwrap(), -10); + /// ``` + #[inline] + #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] + fn max_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item> + where Self: Sized, F: FnMut(&Self::Item) -> B, + { + select_fold1(self, + f, + // switch to y even if it is only equal, to preserve + // stability. + |x_p, _, y_p, _| x_p <= y_p) + .map(|(_, x)| x) + } + + /// Returns the element that gives the minimum value from the + /// specified function. + /// + /// Returns the latest element if the comparison determines two elements + /// to be equally minimum. + /// + /// # Examples + /// + /// ``` + /// let a = [-3_i32, 0, 1, 5, -10]; + /// assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0); + /// ``` + #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] + fn min_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item> + where Self: Sized, F: FnMut(&Self::Item) -> B, + { + select_fold1(self, + f, + // only switch to y if it is strictly smaller, to + // preserve stability. + |x_p, _, y_p, _| x_p > y_p) + .map(|(_, x)| x) + } + + /// Reverses an iterator's direction. + /// + /// Usually, iterators iterate from left to right. After using `rev()`, + /// an iterator will instead iterate from right to left. + /// + /// This is only possible if the iterator has an end, so `rev()` only + /// works on [`DoubleEndedIterator`]s. + /// + /// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html + /// + /// # Examples + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut iter = a.iter().rev(); + /// + /// assert_eq!(iter.next(), Some(&3)); + /// assert_eq!(iter.next(), Some(&2)); + /// assert_eq!(iter.next(), Some(&1)); + /// + /// assert_eq!(iter.next(), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn rev(self) -> Rev<Self> where Self: Sized + DoubleEndedIterator { + Rev{iter: self} + } + + /// Converts an iterator of pairs into a pair of containers. + /// + /// `unzip()` consumes an entire iterator of pairs, producing two + /// collections: one from the left elements of the pairs, and one + /// from the right elements. + /// + /// This function is, in some sense, the opposite of [`zip()`]. + /// + /// [`zip()`]: #method.zip + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [(1, 2), (3, 4)]; + /// + /// let (left, right): (Vec<_>, Vec<_>) = a.iter().cloned().unzip(); + /// + /// assert_eq!(left, [1, 3]); + /// assert_eq!(right, [2, 4]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where + FromA: Default + Extend<A>, + FromB: Default + Extend<B>, + Self: Sized + Iterator<Item=(A, B)>, + { + struct SizeHint<A>(usize, Option<usize>, marker::PhantomData<A>); + impl<A> Iterator for SizeHint<A> { + type Item = A; + + fn next(&mut self) -> Option<A> { None } + fn size_hint(&self) -> (usize, Option<usize>) { + (self.0, self.1) + } + } + + let (lo, hi) = self.size_hint(); + let mut ts: FromA = Default::default(); + let mut us: FromB = Default::default(); + + ts.extend(SizeHint(lo, hi, marker::PhantomData)); + us.extend(SizeHint(lo, hi, marker::PhantomData)); + + for (t, u) in self { + ts.extend(Some(t)); + us.extend(Some(u)); + } + + (ts, us) + } + + /// Creates an iterator which `clone()`s all of its elements. + /// + /// This is useful when you have an iterator over `&T`, but you need an + /// iterator over `T`. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let v_cloned: Vec<_> = a.iter().cloned().collect(); + /// + /// // cloned is the same as .map(|&x| x), for integers + /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); + /// + /// assert_eq!(v_cloned, vec![1, 2, 3]); + /// assert_eq!(v_map, vec![1, 2, 3]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + fn cloned<'a, T: 'a>(self) -> Cloned<Self> + where Self: Sized + Iterator<Item=&'a T>, T: Clone + { + Cloned { it: self } + } + + /// Repeats an iterator endlessly. + /// + /// Instead of stopping at `None`, the iterator will instead start again, + /// from the beginning. After iterating again, it will start at the + /// beginning again. And again. And again. Forever. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// let a = [1, 2, 3]; + /// + /// let mut it = a.iter().cycle(); + /// + /// assert_eq!(it.next(), Some(&1)); + /// assert_eq!(it.next(), Some(&2)); + /// assert_eq!(it.next(), Some(&3)); + /// assert_eq!(it.next(), Some(&1)); + /// assert_eq!(it.next(), Some(&2)); + /// assert_eq!(it.next(), Some(&3)); + /// assert_eq!(it.next(), Some(&1)); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + fn cycle(self) -> Cycle<Self> where Self: Sized + Clone { + Cycle{orig: self.clone(), iter: self} + } + + /// Sums the elements of an iterator. + /// + /// Takes each element, adds them together, and returns the result. + /// + /// An empty iterator returns the zero value of the type. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// #![feature(iter_arith)] + /// + /// let a = [1, 2, 3]; + /// let sum: i32 = a.iter().sum(); + /// + /// assert_eq!(sum, 6); + /// ``` + #[unstable(feature = "iter_arith", reason = "bounds recently changed", + issue = "27739")] + fn sum<S>(self) -> S where + S: Add<Self::Item, Output=S> + Zero, + Self: Sized, + { + self.fold(Zero::zero(), |s, e| s + e) + } + + /// Iterates over the entire iterator, multiplying all the elements + /// + /// An empty iterator returns the one value of the type. + /// + /// # Examples + /// + /// ``` + /// #![feature(iter_arith)] + /// + /// fn factorial(n: u32) -> u32 { + /// (1..).take_while(|&i| i <= n).product() + /// } + /// assert_eq!(factorial(0), 1); + /// assert_eq!(factorial(1), 1); + /// assert_eq!(factorial(5), 120); + /// ``` + #[unstable(feature="iter_arith", reason = "bounds recently changed", + issue = "27739")] + fn product<P>(self) -> P where + P: Mul<Self::Item, Output=P> + One, + Self: Sized, + { + self.fold(One::one(), |p, e| p * e) + } + + /// Lexicographically compares the elements of this `Iterator` with those + /// of another. + #[stable(feature = "iter_order", since = "1.5.0")] + fn cmp<I>(mut self, other: I) -> Ordering where + I: IntoIterator<Item = Self::Item>, + Self::Item: Ord, + Self: Sized, + { + let mut other = other.into_iter(); + + loop { + match (self.next(), other.next()) { + (None, None) => return Ordering::Equal, + (None, _ ) => return Ordering::Less, + (_ , None) => return Ordering::Greater, + (Some(x), Some(y)) => match x.cmp(&y) { + Ordering::Equal => (), + non_eq => return non_eq, + }, + } + } + } + + /// Lexicographically compares the elements of this `Iterator` with those + /// of another. + #[stable(feature = "iter_order", since = "1.5.0")] + fn partial_cmp<I>(mut self, other: I) -> Option<Ordering> where + I: IntoIterator, + Self::Item: PartialOrd<I::Item>, + Self: Sized, + { + let mut other = other.into_iter(); + + loop { + match (self.next(), other.next()) { + (None, None) => return Some(Ordering::Equal), + (None, _ ) => return Some(Ordering::Less), + (_ , None) => return Some(Ordering::Greater), + (Some(x), Some(y)) => match x.partial_cmp(&y) { + Some(Ordering::Equal) => (), + non_eq => return non_eq, + }, + } + } + } + + /// Determines if the elements of this `Iterator` are equal to those of + /// another. + #[stable(feature = "iter_order", since = "1.5.0")] + fn eq<I>(mut self, other: I) -> bool where + I: IntoIterator, + Self::Item: PartialEq<I::Item>, + Self: Sized, + { + let mut other = other.into_iter(); + + loop { + match (self.next(), other.next()) { + (None, None) => return true, + (None, _) | (_, None) => return false, + (Some(x), Some(y)) => if x != y { return false }, + } + } + } + + /// Determines if the elements of this `Iterator` are unequal to those of + /// another. + #[stable(feature = "iter_order", since = "1.5.0")] + fn ne<I>(mut self, other: I) -> bool where + I: IntoIterator, + Self::Item: PartialEq<I::Item>, + Self: Sized, + { + let mut other = other.into_iter(); + + loop { + match (self.next(), other.next()) { + (None, None) => return false, + (None, _) | (_, None) => return true, + (Some(x), Some(y)) => if x.ne(&y) { return true }, + } + } + } + + /// Determines if the elements of this `Iterator` are lexicographically + /// less than those of another. + #[stable(feature = "iter_order", since = "1.5.0")] + fn lt<I>(mut self, other: I) -> bool where + I: IntoIterator, + Self::Item: PartialOrd<I::Item>, + Self: Sized, + { + let mut other = other.into_iter(); + + loop { + match (self.next(), other.next()) { + (None, None) => return false, + (None, _ ) => return true, + (_ , None) => return false, + (Some(x), Some(y)) => { + match x.partial_cmp(&y) { + Some(Ordering::Less) => return true, + Some(Ordering::Equal) => {} + Some(Ordering::Greater) => return false, + None => return false, + } + }, + } + } + } + + /// Determines if the elements of this `Iterator` are lexicographically + /// less or equal to those of another. + #[stable(feature = "iter_order", since = "1.5.0")] + fn le<I>(mut self, other: I) -> bool where + I: IntoIterator, + Self::Item: PartialOrd<I::Item>, + Self: Sized, + { + let mut other = other.into_iter(); + + loop { + match (self.next(), other.next()) { + (None, None) => return true, + (None, _ ) => return true, + (_ , None) => return false, + (Some(x), Some(y)) => { + match x.partial_cmp(&y) { + Some(Ordering::Less) => return true, + Some(Ordering::Equal) => {} + Some(Ordering::Greater) => return false, + None => return false, + } + }, + } + } + } + + /// Determines if the elements of this `Iterator` are lexicographically + /// greater than those of another. + #[stable(feature = "iter_order", since = "1.5.0")] + fn gt<I>(mut self, other: I) -> bool where + I: IntoIterator, + Self::Item: PartialOrd<I::Item>, + Self: Sized, + { + let mut other = other.into_iter(); + + loop { + match (self.next(), other.next()) { + (None, None) => return false, + (None, _ ) => return false, + (_ , None) => return true, + (Some(x), Some(y)) => { + match x.partial_cmp(&y) { + Some(Ordering::Less) => return false, + Some(Ordering::Equal) => {} + Some(Ordering::Greater) => return true, + None => return false, + } + } + } + } + } + + /// Determines if the elements of this `Iterator` are lexicographically + /// greater than or equal to those of another. + #[stable(feature = "iter_order", since = "1.5.0")] + fn ge<I>(mut self, other: I) -> bool where + I: IntoIterator, + Self::Item: PartialOrd<I::Item>, + Self: Sized, + { + let mut other = other.into_iter(); + + loop { + match (self.next(), other.next()) { + (None, None) => return true, + (None, _ ) => return false, + (_ , None) => return true, + (Some(x), Some(y)) => { + match x.partial_cmp(&y) { + Some(Ordering::Less) => return false, + Some(Ordering::Equal) => {} + Some(Ordering::Greater) => return true, + None => return false, + } + }, + } + } + } +} + +/// Select an element from an iterator based on the given projection +/// and "comparison" function. +/// +/// This is an idiosyncratic helper to try to factor out the +/// commonalities of {max,min}{,_by}. In particular, this avoids +/// having to implement optimizations several times. +#[inline] +fn select_fold1<I,B, FProj, FCmp>(mut it: I, + mut f_proj: FProj, + mut f_cmp: FCmp) -> Option<(B, I::Item)> + where I: Iterator, + FProj: FnMut(&I::Item) -> B, + FCmp: FnMut(&B, &I::Item, &B, &I::Item) -> bool +{ + // start with the first element as our selection. This avoids + // having to use `Option`s inside the loop, translating to a + // sizeable performance gain (6x in one case). + it.next().map(|mut sel| { + let mut sel_p = f_proj(&sel); + + for x in it { + let x_p = f_proj(&x); + if f_cmp(&sel_p, &sel, &x_p, &x) { + sel = x; + sel_p = x_p; + } + } + (sel_p, sel) + }) +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, I: Iterator + ?Sized> Iterator for &'a mut I { + type Item = I::Item; + fn next(&mut self) -> Option<I::Item> { (**self).next() } + fn size_hint(&self) -> (usize, Option<usize>) { (**self).size_hint() } +} + |