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// 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 ops::FnMut;
use option::Option::{self, Some, None};
use marker::Sized;
use super::{Chain, Cycle, Cloned, Enumerate, Filter, FilterMap, FlatMap, Fuse};
use super::{Inspect, Map, Peekable, Scan, Skip, SkipWhile, Take, TakeWhile, Rev};
use super::{Zip, Sum, Product};
use super::ChainState;
use super::{DoubleEndedIterator, ExactSizeIterator, Extend, FromIterator};
use super::{IntoIterator, ZipImpl};
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]
#[rustc_inherit_overflow_checks]
#[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 greater than or equal to 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 + 1` 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::new(self, 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 = ['a', 'b', 'c'];
///
/// let mut iter = a.iter().enumerate();
///
/// assert_eq!(iter.next(), Some((0, &'a')));
/// assert_eq!(iter.next(), Some((1, &'b')));
/// assert_eq!(iter.next(), Some((2, &'c')));
/// 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)>,
{
let mut ts: FromA = Default::default();
let mut us: FromB = Default::default();
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.
///
/// # Panics
///
/// When calling `sum` and a primitive integer type is being returned, this
/// method will panic if the computation overflows.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
/// let sum: i32 = a.iter().sum();
///
/// assert_eq!(sum, 6);
/// ```
#[stable(feature = "iter_arith", since = "1.11.0")]
fn sum<S>(self) -> S
where Self: Sized,
S: Sum<Self::Item>,
{
Sum::sum(self)
}
/// Iterates over the entire iterator, multiplying all the elements
///
/// An empty iterator returns the one value of the type.
///
/// # Panics
///
/// When calling `product` and a primitive integer type is being returned,
/// this method will panic if the computation overflows.
///
/// # Examples
///
/// ```
/// 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);
/// ```
#[stable(feature = "iter_arith", since = "1.11.0")]
fn product<P>(self) -> P
where Self: Sized,
P: Product<Self::Item>,
{
Product::product(self)
}
/// 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() }
}