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// Copyright 2013-2014 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.
//! Composable external iteration
//!
//! If you've found yourself with a collection of some kind, and needed to
//! perform an operation on the elements of said collection, you'll quickly run
//! into 'iterators'. Iterators are heavily used in idiomatic Rust code, so
//! it's worth becoming familiar with them.
//!
//! Before explaining more, let's talk about how this module is structured:
//!
//! # Organization
//!
//! This module is largely organized by type:
//!
//! * [Traits] are the core portion: these traits define what kind of iterators
//! exist and what you can do with them. The methods of these traits are worth
//! putting some extra study time into.
//! * [Functions] provide some helpful ways to create some basic iterators.
//! * [Structs] are often the return types of the various methods on this
//! module's traits. You'll usually want to look at the method that creates
//! the `struct`, rather than the `struct` itself. For more detail about why,
//! see '[Implementing Iterator](#implementing-iterator)'.
//!
//! [Traits]: #traits
//! [Functions]: #functions
//! [Structs]: #structs
//!
//! That's it! Let's dig into iterators.
//!
//! # Iterator
//!
//! The heart and soul of this module is the [`Iterator`] trait. The core of
//! [`Iterator`] looks like this:
//!
//! ```
//! trait Iterator {
//! type Item;
//! fn next(&mut self) -> Option<Self::Item>;
//! }
//! ```
//!
//! An iterator has a method, [`next()`], which when called, returns an
//! [`Option`]`<Item>`. [`next()`] will return `Some(Item)` as long as there
//! are elements, and once they've all been exhausted, will return `None` to
//! indicate that iteration is finished. Individual iterators may choose to
//! resume iteration, and so calling [`next()`] again may or may not eventually
//! start returning `Some(Item)` again at some point.
//!
//! [`Iterator`]'s full definition includes a number of other methods as well,
//! but they are default methods, built on top of [`next()`], and so you get
//! them for free.
//!
//! Iterators are also composable, and it's common to chain them together to do
//! more complex forms of processing. See the [Adapters](#adapters) section
//! below for more details.
//!
//! [`Iterator`]: trait.Iterator.html
//! [`next()`]: trait.Iterator.html#tymethod.next
//! [`Option`]: ../option/enum.Option.html
//!
//! # The three forms of iteration
//!
//! There are three common methods which can create iterators from a collection:
//!
//! * `iter()`, which iterates over `&T`.
//! * `iter_mut()`, which iterates over `&mut T`.
//! * `into_iter()`, which iterates over `T`.
//!
//! Various things in the standard library may implement one or more of the
//! three, where appropriate.
//!
//! # Implementing Iterator
//!
//! Creating an iterator of your own involves two steps: creating a `struct` to
//! hold the iterator's state, and then `impl`ementing [`Iterator`] for that
//! `struct`. This is why there are so many `struct`s in this module: there is
//! one for each iterator and iterator adapter.
//!
//! Let's make an iterator named `Counter` which counts from `1` to `5`:
//!
//! ```
//! // First, the struct:
//!
//! /// An iterator which counts from one to five
//! struct Counter {
//! count: usize,
//! }
//!
//! // we want our count to start at one, so let's add a new() method to help.
//! // This isn't strictly necessary, but is convenient. Note that we start
//! // `count` at zero, we'll see why in `next()`'s implementation below.
//! impl Counter {
//! fn new() -> Counter {
//! Counter { count: 0 }
//! }
//! }
//!
//! // Then, we implement `Iterator` for our `Counter`:
//!
//! impl Iterator for Counter {
//! // we will be counting with usize
//! type Item = usize;
//!
//! // next() is the only required method
//! fn next(&mut self) -> Option<usize> {
//! // increment our count. This is why we started at zero.
//! self.count += 1;
//!
//! // check to see if we've finished counting or not.
//! if self.count < 6 {
//! Some(self.count)
//! } else {
//! None
//! }
//! }
//! }
//!
//! // And now we can use it!
//!
//! let mut counter = Counter::new();
//!
//! let x = counter.next().unwrap();
//! println!("{}", x);
//!
//! let x = counter.next().unwrap();
//! println!("{}", x);
//!
//! let x = counter.next().unwrap();
//! println!("{}", x);
//!
//! let x = counter.next().unwrap();
//! println!("{}", x);
//!
//! let x = counter.next().unwrap();
//! println!("{}", x);
//! ```
//!
//! This will print `1` through `5`, each on their own line.
//!
//! Calling `next()` this way gets repetitive. Rust has a construct which can
//! call `next()` on your iterator, until it reaches `None`. Let's go over that
//! next.
//!
//! # for Loops and IntoIterator
//!
//! Rust's `for` loop syntax is actually sugar for iterators. Here's a basic
//! example of `for`:
//!
//! ```
//! let values = vec![1, 2, 3, 4, 5];
//!
//! for x in values {
//! println!("{}", x);
//! }
//! ```
//!
//! This will print the numbers one through five, each on their own line. But
//! you'll notice something here: we never called anything on our vector to
//! produce an iterator. What gives?
//!
//! There's a trait in the standard library for converting something into an
//! iterator: [`IntoIterator`]. This trait has one method, [`into_iter()`],
//! which converts the thing implementing [`IntoIterator`] into an iterator.
//! Let's take a look at that `for` loop again, and what the compiler converts
//! it into:
//!
//! [`IntoIterator`]: trait.IntoIterator.html
//! [`into_iter()`]: trait.IntoIterator.html#tymethod.into_iter
//!
//! ```
//! let values = vec![1, 2, 3, 4, 5];
//!
//! for x in values {
//! println!("{}", x);
//! }
//! ```
//!
//! Rust de-sugars this into:
//!
//! ```
//! let values = vec![1, 2, 3, 4, 5];
//! {
//! let result = match values.into_iter() {
//! mut iter => loop {
//! match iter.next() {
//! Some(x) => { println!("{}", x); },
//! None => break,
//! }
//! },
//! };
//! result
//! }
//! ```
//!
//! First, we call `into_iter()` on the value. Then, we match on the iterator
//! that returns, calling [`next()`] over and over until we see a `None`. At
//! that point, we `break` out of the loop, and we're done iterating.
//!
//! There's one more subtle bit here: the standard library contains an
//! interesting implementation of [`IntoIterator`]:
//!
//! ```ignore
//! impl<I: Iterator> IntoIterator for I
//! ```
//!
//! In other words, all [`Iterator`]s implement [`IntoIterator`], by just
//! returning themselves. This means two things:
//!
//! 1. If you're writing an [`Iterator`], you can use it with a `for` loop.
//! 2. If you're creating a collection, implementing [`IntoIterator`] for it
//! will allow your collection to be used with the `for` loop.
//!
//! # Adapters
//!
//! Functions which take an [`Iterator`] and return another [`Iterator`] are
//! often called 'iterator adapters', as they're a form of the 'adapter
//! pattern'.
//!
//! Common iterator adapters include [`map()`], [`take()`], and [`collect()`].
//! For more, see their documentation.
//!
//! [`map()`]: trait.Iterator.html#method.map
//! [`take()`]: trait.Iterator.html#method.take
//! [`collect()`]: trait.Iterator.html#method.collect
//!
//! # Laziness
//!
//! Iterators (and iterator [adapters](#adapters)) are *lazy*. This means that
//! just creating an iterator doesn't _do_ a whole lot. Nothing really happens
//! until you call [`next()`]. This is sometimes a source of confusion when
//! creating an iterator solely for its side effects. For example, the [`map()`]
//! method calls a closure on each element it iterates over:
//!
//! ```
//! # #![allow(unused_must_use)]
//! let v = vec![1, 2, 3, 4, 5];
//! v.iter().map(|x| println!("{}", x));
//! ```
//!
//! This will not print any values, as we only created an iterator, rather than
//! using it. The compiler will warn us about this kind of behavior:
//!
//! ```text
//! warning: unused result which must be used: iterator adaptors are lazy and
//! do nothing unless consumed
//! ```
//!
//! The idiomatic way to write a [`map()`] for its side effects is to use a
//! `for` loop instead:
//!
//! ```
//! let v = vec![1, 2, 3, 4, 5];
//!
//! for x in &v {
//! println!("{}", x);
//! }
//! ```
//!
//! [`map()`]: trait.Iterator.html#method.map
//!
//! The two most common ways to evaluate an iterator are to use a `for` loop
//! like this, or using the [`collect()`] adapter to produce a new collection.
//!
//! [`collect()`]: trait.Iterator.html#method.collect
//!
//! # Infinity
//!
//! Iterators do not have to be finite. As an example, an open-ended range is
//! an infinite iterator:
//!
//! ```
//! let numbers = 0..;
//! ```
//!
//! It is common to use the [`take()`] iterator adapter to turn an infinite
//! iterator into a finite one:
//!
//! ```
//! let numbers = 0..;
//! let five_numbers = numbers.take(5);
//!
//! for number in five_numbers {
//! println!("{}", number);
//! }
//! ```
//!
//! This will print the numbers `0` through `4`, each on their own line.
//!
//! [`take()`]: trait.Iterator.html#method.take
#![stable(feature = "rust1", since = "1.0.0")]
use clone::Clone;
use cmp;
use cmp::{Ord, PartialOrd, PartialEq, Ordering};
use default::Default;
use marker;
use mem;
use num::{Zero, One};
use ops::{self, Add, Sub, FnMut, Mul, RangeFrom};
use option::Option::{self, Some, None};
use marker::Sized;
use usize;
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()`]: #method.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()`]: #method.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>`]: ../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`]: ../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`]: ../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 look at the `next()` element without
/// consuming it.
///
/// Adds a [`peek()`] method to an iterator. See its documentation for
/// more information.
///
/// [`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);
/// ```
#[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`]: ../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`]: ../string/struct.String.html
/// [`Result<T, E>`]: ../result/enum.Result.html
/// [`char`]: ../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>`]: ../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 annotationg `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. It 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-circuting; 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-circuting; 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-circuting; 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-circuting; 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-circuting; 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)
}
#[allow(missing_docs)]
#[inline]
#[unstable(feature = "iter_cmp",
reason = "may want to produce an Ordering directly; see #15311",
issue = "27724")]
#[rustc_deprecated(reason = "renamed to max_by_key", since = "1.6.0")]
fn max_by<B: Ord, F>(self, f: F) -> Option<Self::Item> where
Self: Sized,
F: FnMut(&Self::Item) -> B,
{
self.max_by_key(f)
}
/// 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)
}
#[inline]
#[allow(missing_docs)]
#[unstable(feature = "iter_cmp",
reason = "may want to produce an Ordering directly; see #15311",
issue = "27724")]
#[rustc_deprecated(reason = "renamed to min_by_key", since = "1.6.0")]
fn min_by<B: Ord, F>(self, f: F) -> Option<Self::Item> where
Self: Sized,
F: FnMut(&Self::Item) -> B,
{
self.min_by_key(f)
}
/// 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() }
}
/// Conversion from an `Iterator`.
///
/// By implementing `FromIterator` for a type, you define how it will be
/// created from an iterator. This is common for types which describe a
/// collection of some kind.
///
/// `FromIterator`'s [`from_iter()`] is rarely called explicitly, and is instead
/// used through [`Iterator`]'s [`collect()`] method. See [`collect()`]'s
/// documentation for more examples.
///
/// [`from_iter()`]: #tymethod.from_iter
/// [`Iterator`]: trait.Iterator.html
/// [`collect()`]: trait.Iterator.html#method.collect
///
/// See also: [`IntoIterator`].
///
/// [`IntoIterator`]: trait.IntoIterator.html
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter::FromIterator;
///
/// let five_fives = std::iter::repeat(5).take(5);
///
/// let v = Vec::from_iter(five_fives);
///
/// assert_eq!(v, vec![5, 5, 5, 5, 5]);
/// ```
///
/// Using [`collect()`] to implicitly use `FromIterator`:
///
/// ```
/// let five_fives = std::iter::repeat(5).take(5);
///
/// let v: Vec<i32> = five_fives.collect();
///
/// assert_eq!(v, vec![5, 5, 5, 5, 5]);
/// ```
///
/// Implementing `FromIterator` for your type:
///
/// ```
/// use std::iter::FromIterator;
///
/// // A sample collection, that's just a wrapper over Vec<T>
/// #[derive(Debug)]
/// struct MyCollection(Vec<i32>);
///
/// // Let's give it some methods so we can create one and add things
/// // to it.
/// impl MyCollection {
/// fn new() -> MyCollection {
/// MyCollection(Vec::new())
/// }
///
/// fn add(&mut self, elem: i32) {
/// self.0.push(elem);
/// }
/// }
///
/// // and we'll implement FromIterator
/// impl FromIterator<i32> for MyCollection {
/// fn from_iter<I: IntoIterator<Item=i32>>(iterator: I) -> Self {
/// let mut c = MyCollection::new();
///
/// for i in iterator {
/// c.add(i);
/// }
///
/// c
/// }
/// }
///
/// // Now we can make a new iterator...
/// let iter = (0..5).into_iter();
///
/// // ... and make a MyCollection out of it
/// let c = MyCollection::from_iter(iter);
///
/// assert_eq!(c.0, vec![0, 1, 2, 3, 4]);
///
/// // collect works too!
///
/// let iter = (0..5).into_iter();
/// let c: MyCollection = iter.collect();
///
/// assert_eq!(c.0, vec![0, 1, 2, 3, 4]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_on_unimplemented="a collection of type `{Self}` cannot be \
built from an iterator over elements of type `{A}`"]
pub trait FromIterator<A>: Sized {
/// Creates a value from an iterator.
///
/// See the [module-level documentation] for more.
///
/// [module-level documentation]: trait.FromIterator.html
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter::FromIterator;
///
/// let five_fives = std::iter::repeat(5).take(5);
///
/// let v = Vec::from_iter(five_fives);
///
/// assert_eq!(v, vec![5, 5, 5, 5, 5]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn from_iter<T: IntoIterator<Item=A>>(iterator: T) -> Self;
}
/// Conversion into an `Iterator`.
///
/// By implementing `IntoIterator` for a type, you define how it will be
/// converted to an iterator. This is common for types which describe a
/// collection of some kind.
///
/// One benefit of implementing `IntoIterator` is that your type will [work
/// with Rust's `for` loop syntax](index.html#for-loops-and-intoiterator).
///
/// See also: [`FromIterator`].
///
/// [`FromIterator`]: trait.FromIterator.html
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let v = vec![1, 2, 3];
///
/// let mut iter = v.into_iter();
///
/// let n = iter.next();
/// assert_eq!(Some(1), n);
///
/// let n = iter.next();
/// assert_eq!(Some(2), n);
///
/// let n = iter.next();
/// assert_eq!(Some(3), n);
///
/// let n = iter.next();
/// assert_eq!(None, n);
/// ```
///
/// Implementing `IntoIterator` for your type:
///
/// ```
/// // A sample collection, that's just a wrapper over Vec<T>
/// #[derive(Debug)]
/// struct MyCollection(Vec<i32>);
///
/// // Let's give it some methods so we can create one and add things
/// // to it.
/// impl MyCollection {
/// fn new() -> MyCollection {
/// MyCollection(Vec::new())
/// }
///
/// fn add(&mut self, elem: i32) {
/// self.0.push(elem);
/// }
/// }
///
/// // and we'll implement IntoIterator
/// impl IntoIterator for MyCollection {
/// type Item = i32;
/// type IntoIter = ::std::vec::IntoIter<i32>;
///
/// fn into_iter(self) -> Self::IntoIter {
/// self.0.into_iter()
/// }
/// }
///
/// // Now we can make a new collection...
/// let mut c = MyCollection::new();
///
/// // ... add some stuff to it ...
/// c.add(0);
/// c.add(1);
/// c.add(2);
///
/// // ... and then turn it into an Iterator:
/// for (i, n) in c.into_iter().enumerate() {
/// assert_eq!(i as i32, n);
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait IntoIterator {
/// The type of the elements being iterated over.
#[stable(feature = "rust1", since = "1.0.0")]
type Item;
/// Which kind of iterator are we turning this into?
#[stable(feature = "rust1", since = "1.0.0")]
type IntoIter: Iterator<Item=Self::Item>;
/// Creates an iterator from a value.
///
/// See the [module-level documentation] for more.
///
/// [module-level documentation]: trait.IntoIterator.html
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let v = vec![1, 2, 3];
///
/// let mut iter = v.into_iter();
///
/// let n = iter.next();
/// assert_eq!(Some(1), n);
///
/// let n = iter.next();
/// assert_eq!(Some(2), n);
///
/// let n = iter.next();
/// assert_eq!(Some(3), n);
///
/// let n = iter.next();
/// assert_eq!(None, n);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn into_iter(self) -> Self::IntoIter;
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator> IntoIterator for I {
type Item = I::Item;
type IntoIter = I;
fn into_iter(self) -> I {
self
}
}
/// Extend a collection with the contents of an iterator.
///
/// Iterators produce a series of values, and collections can also be thought
/// of as a series of values. The `Extend` trait bridges this gap, allowing you
/// to extend a collection by including the contents of that iterator.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// // You can extend a String with some chars:
/// let mut message = String::from("The first three letters are: ");
///
/// message.extend(&['a', 'b', 'c']);
///
/// assert_eq!("abc", &message[29..32]);
/// ```
///
/// Implementing `Extend`:
///
/// ```
/// // A sample collection, that's just a wrapper over Vec<T>
/// #[derive(Debug)]
/// struct MyCollection(Vec<i32>);
///
/// // Let's give it some methods so we can create one and add things
/// // to it.
/// impl MyCollection {
/// fn new() -> MyCollection {
/// MyCollection(Vec::new())
/// }
///
/// fn add(&mut self, elem: i32) {
/// self.0.push(elem);
/// }
/// }
///
/// // since MyCollection has a list of i32s, we implement Extend for i32
/// impl Extend<i32> for MyCollection {
///
/// // This is a bit simpler with the concrete type signature: we can call
/// // extend on anything which can be turned into an Iterator which gives
/// // us i32s. Because we need i32s to put into MyCollection.
/// fn extend<T: IntoIterator<Item=i32>>(&mut self, iterable: T) {
///
/// // The implementation is very straightforward: loop through the
/// // iterator, and add() each element to ourselves.
/// for elem in iterable {
/// self.add(elem);
/// }
/// }
/// }
///
/// let mut c = MyCollection::new();
///
/// c.add(5);
/// c.add(6);
/// c.add(7);
///
/// // let's extend our collection with three more numbers
/// c.extend(vec![1, 2, 3]);
///
/// // we've added these elements onto the end
/// assert_eq!("MyCollection([5, 6, 7, 1, 2, 3])", format!("{:?}", c));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Extend<A> {
/// Extends a collection with the contents of an iterator.
///
/// As this is the only method for this trait, the [trait-level] docs
/// contain more details.
///
/// [trait-level]: trait.Extend.html
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// // You can extend a String with some chars:
/// let mut message = String::from("abc");
///
/// message.extend(['d', 'e', 'f'].iter());
///
/// assert_eq!("abcdef", &message);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn extend<T: IntoIterator<Item=A>>(&mut self, iterable: T);
}
/// An iterator able to yield elements from both ends.
///
/// Something that implements `DoubleEndedIterator` has one extra capability
/// over something that implements [`Iterator`]: the ability to also take
/// `Item`s from the back, as well as the front.
///
/// It is important to note that both back and forth work on the same range,
/// and do not cross: iteration is over when they meet in the middle.
///
/// [`Iterator`]: trait.Iterator.html
/// # Examples
///
/// Basic usage:
///
/// ```
/// let numbers = vec![1, 2, 3];
///
/// let mut iter = numbers.iter();
///
/// let n = iter.next();
/// assert_eq!(Some(&1), n);
///
/// let n = iter.next_back();
/// assert_eq!(Some(&3), n);
///
/// let n = iter.next_back();
/// assert_eq!(Some(&2), n);
///
/// let n = iter.next();
/// assert_eq!(None, n);
///
/// let n = iter.next_back();
/// assert_eq!(None, n);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait DoubleEndedIterator: Iterator {
/// An iterator able to yield elements from both ends.
///
/// As this is the only method for this trait, the [trait-level] docs
/// contain more details.
///
/// [trait-level]: trait.DoubleEndedIterator.html
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let numbers = vec![1, 2, 3];
///
/// let mut iter = numbers.iter();
///
/// let n = iter.next();
/// assert_eq!(Some(&1), n);
///
/// let n = iter.next_back();
/// assert_eq!(Some(&3), n);
///
/// let n = iter.next_back();
/// assert_eq!(Some(&2), n);
///
/// let n = iter.next();
/// assert_eq!(None, n);
///
/// let n = iter.next_back();
/// assert_eq!(None, n);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn next_back(&mut self) -> Option<Self::Item>;
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for &'a mut I {
fn next_back(&mut self) -> Option<I::Item> { (**self).next_back() }
}
/// An iterator that knows its exact length.
///
/// Many [`Iterator`]s don't know how many times they will iterate, but some do.
/// If an iterator knows how many times it can iterate, providing access to
/// that information can be useful. For example, if you want to iterate
/// backwards, a good start is to know where the end is.
///
/// When implementing an `ExactSizeIterator`, You must also implement
/// [`Iterator`]. When doing so, the implementation of [`size_hint()`] *must*
/// return the exact size of the iterator.
///
/// [`Iterator`]: trait.Iterator.html
/// [`size_hint()`]: trait.Iterator.html#method.size_hint
///
/// The [`len()`] method has a default implementation, so you usually shouldn't
/// implement it. However, you may be able to provide a more performant
/// implementation than the default, so overriding it in this case makes sense.
///
/// [`len()`]: #method.len
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// // a finite range knows exactly how many times it will iterate
/// let five = 0..5;
///
/// assert_eq!(5, five.len());
/// ```
///
/// In the [module level docs][moddocs], we implemented an [`Iterator`],
/// `Counter`. Let's implement `ExactSizeIterator` for it as well:
///
/// [moddocs]: index.html
///
/// ```
/// # struct Counter {
/// # count: usize,
/// # }
/// # impl Counter {
/// # fn new() -> Counter {
/// # Counter { count: 0 }
/// # }
/// # }
/// # impl Iterator for Counter {
/// # type Item = usize;
/// # fn next(&mut self) -> Option<usize> {
/// # self.count += 1;
/// # if self.count < 6 {
/// # Some(self.count)
/// # } else {
/// # None
/// # }
/// # }
/// # }
/// impl ExactSizeIterator for Counter {
/// // We already have the number of iterations, so we can use it directly.
/// fn len(&self) -> usize {
/// self.count
/// }
/// }
///
/// // And now we can use it!
///
/// let counter = Counter::new();
///
/// assert_eq!(0, counter.len());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait ExactSizeIterator: Iterator {
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
/// Returns the exact number of times the iterator will iterate.
///
/// This method has a default implementation, so you usually should not
/// implement it directly. However, if you can provide a more efficient
/// implementation, you can do so. See the [trait-level] docs for an
/// example.
///
/// This function has the same safety guarantees as the [`size_hint()`]
/// function.
///
/// [trait-level]: trait.ExactSizeIterator.html
/// [`size_hint()`]: trait.Iterator.html#method.size_hint
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// // a finite range knows exactly how many times it will iterate
/// let five = 0..5;
///
/// assert_eq!(5, five.len());
/// ```
fn len(&self) -> usize {
let (lower, upper) = self.size_hint();
// Note: This assertion is overly defensive, but it checks the invariant
// guaranteed by the trait. If this trait were rust-internal,
// we could use debug_assert!; assert_eq! will check all Rust user
// implementations too.
assert_eq!(upper, Some(lower));
lower
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, I: ExactSizeIterator + ?Sized> ExactSizeIterator for &'a mut I {}
// All adaptors that preserve the size of the wrapped iterator are fine
// Adaptors that may overflow in `size_hint` are not, i.e. `Chain`.
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Enumerate<I> where I: ExactSizeIterator {}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: ExactSizeIterator, F> ExactSizeIterator for Inspect<I, F> where
F: FnMut(&I::Item),
{}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Rev<I>
where I: ExactSizeIterator + DoubleEndedIterator {}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: ExactSizeIterator, F> ExactSizeIterator for Map<I, F> where
F: FnMut(I::Item) -> B,
{}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B> ExactSizeIterator for Zip<A, B>
where A: ExactSizeIterator, B: ExactSizeIterator {}
/// An double-ended iterator with the direction inverted.
///
/// This `struct` is created by the [`rev()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`rev()`]: trait.Iterator.html#method.rev
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Rev<T> {
iter: T
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Rev<I> where I: DoubleEndedIterator {
type Item = <I as Iterator>::Item;
#[inline]
fn next(&mut self) -> Option<<I as Iterator>::Item> { self.iter.next_back() }
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> DoubleEndedIterator for Rev<I> where I: DoubleEndedIterator {
#[inline]
fn next_back(&mut self) -> Option<<I as Iterator>::Item> { self.iter.next() }
}
/// An iterator that clones the elements of an underlying iterator.
///
/// This `struct` is created by the [`cloned()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`cloned()`]: trait.Iterator.html#method.cloned
/// [`Iterator`]: trait.Iterator.html
#[stable(feature = "iter_cloned", since = "1.1.0")]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[derive(Clone)]
pub struct Cloned<I> {
it: I,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, I, T: 'a> Iterator for Cloned<I>
where I: Iterator<Item=&'a T>, T: Clone
{
type Item = T;
fn next(&mut self) -> Option<T> {
self.it.next().cloned()
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.it.size_hint()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, I, T: 'a> DoubleEndedIterator for Cloned<I>
where I: DoubleEndedIterator<Item=&'a T>, T: Clone
{
fn next_back(&mut self) -> Option<T> {
self.it.next_back().cloned()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, I, T: 'a> ExactSizeIterator for Cloned<I>
where I: ExactSizeIterator<Item=&'a T>, T: Clone
{}
/// An iterator that repeats endlessly.
///
/// This `struct` is created by the [`cycle()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`cycle()`]: trait.Iterator.html#method.cycle
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Cycle<I> {
orig: I,
iter: I,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Cycle<I> where I: Clone + Iterator {
type Item = <I as Iterator>::Item;
#[inline]
fn next(&mut self) -> Option<<I as Iterator>::Item> {
match self.iter.next() {
None => { self.iter = self.orig.clone(); self.iter.next() }
y => y
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
// the cycle iterator is either empty or infinite
match self.orig.size_hint() {
sz @ (0, Some(0)) => sz,
(0, _) => (0, None),
_ => (usize::MAX, None)
}
}
}
/// An iterator that strings two iterators together.
///
/// This `struct` is created by the [`chain()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`chain()`]: trait.Iterator.html#method.chain
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Chain<A, B> {
a: A,
b: B,
state: ChainState,
}
// The iterator protocol specifies that iteration ends with the return value
// `None` from `.next()` (or `.next_back()`) and it is unspecified what
// further calls return. The chain adaptor must account for this since it uses
// two subiterators.
//
// It uses three states:
//
// - Both: `a` and `b` are remaining
// - Front: `a` remaining
// - Back: `b` remaining
//
// The fourth state (neither iterator is remaining) only occurs after Chain has
// returned None once, so we don't need to store this state.
#[derive(Clone)]
enum ChainState {
// both front and back iterator are remaining
Both,
// only front is remaining
Front,
// only back is remaining
Back,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B> Iterator for Chain<A, B> where
A: Iterator,
B: Iterator<Item = A::Item>
{
type Item = A::Item;
#[inline]
fn next(&mut self) -> Option<A::Item> {
match self.state {
ChainState::Both => match self.a.next() {
elt @ Some(..) => elt,
None => {
self.state = ChainState::Back;
self.b.next()
}
},
ChainState::Front => self.a.next(),
ChainState::Back => self.b.next(),
}
}
#[inline]
fn count(self) -> usize {
match self.state {
ChainState::Both => self.a.count() + self.b.count(),
ChainState::Front => self.a.count(),
ChainState::Back => self.b.count(),
}
}
#[inline]
fn nth(&mut self, mut n: usize) -> Option<A::Item> {
match self.state {
ChainState::Both | ChainState::Front => {
for x in self.a.by_ref() {
if n == 0 {
return Some(x)
}
n -= 1;
}
if let ChainState::Both = self.state {
self.state = ChainState::Back;
}
}
ChainState::Back => {}
}
if let ChainState::Back = self.state {
self.b.nth(n)
} else {
None
}
}
#[inline]
fn last(self) -> Option<A::Item> {
match self.state {
ChainState::Both => {
// Must exhaust a before b.
let a_last = self.a.last();
let b_last = self.b.last();
b_last.or(a_last)
},
ChainState::Front => self.a.last(),
ChainState::Back => self.b.last()
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (a_lower, a_upper) = self.a.size_hint();
let (b_lower, b_upper) = self.b.size_hint();
let lower = a_lower.saturating_add(b_lower);
let upper = match (a_upper, b_upper) {
(Some(x), Some(y)) => x.checked_add(y),
_ => None
};
(lower, upper)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B> DoubleEndedIterator for Chain<A, B> where
A: DoubleEndedIterator,
B: DoubleEndedIterator<Item=A::Item>,
{
#[inline]
fn next_back(&mut self) -> Option<A::Item> {
match self.state {
ChainState::Both => match self.b.next_back() {
elt @ Some(..) => elt,
None => {
self.state = ChainState::Front;
self.a.next_back()
}
},
ChainState::Front => self.a.next_back(),
ChainState::Back => self.b.next_back(),
}
}
}
/// An iterator that iterates two other iterators simultaneously.
///
/// This `struct` is created by the [`zip()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`zip()`]: trait.Iterator.html#method.zip
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Zip<A, B> {
a: A,
b: B
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B> Iterator for Zip<A, B> where A: Iterator, B: Iterator
{
type Item = (A::Item, B::Item);
#[inline]
fn next(&mut self) -> Option<(A::Item, B::Item)> {
self.a.next().and_then(|x| {
self.b.next().and_then(|y| {
Some((x, y))
})
})
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (a_lower, a_upper) = self.a.size_hint();
let (b_lower, b_upper) = self.b.size_hint();
let lower = cmp::min(a_lower, b_lower);
let upper = match (a_upper, b_upper) {
(Some(x), Some(y)) => Some(cmp::min(x,y)),
(Some(x), None) => Some(x),
(None, Some(y)) => Some(y),
(None, None) => None
};
(lower, upper)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B> DoubleEndedIterator for Zip<A, B> where
A: DoubleEndedIterator + ExactSizeIterator,
B: DoubleEndedIterator + ExactSizeIterator,
{
#[inline]
fn next_back(&mut self) -> Option<(A::Item, B::Item)> {
let a_sz = self.a.len();
let b_sz = self.b.len();
if a_sz != b_sz {
// Adjust a, b to equal length
if a_sz > b_sz {
for _ in 0..a_sz - b_sz { self.a.next_back(); }
} else {
for _ in 0..b_sz - a_sz { self.b.next_back(); }
}
}
match (self.a.next_back(), self.b.next_back()) {
(Some(x), Some(y)) => Some((x, y)),
(None, None) => None,
_ => unreachable!(),
}
}
}
/// An iterator that maps the values of `iter` with `f`.
///
/// This `struct` is created by the [`map()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`map()`]: trait.Iterator.html#method.map
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Map<I, F> {
iter: I,
f: F,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: Iterator, F> Iterator for Map<I, F> where F: FnMut(I::Item) -> B {
type Item = B;
#[inline]
fn next(&mut self) -> Option<B> {
self.iter.next().map(&mut self.f)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for Map<I, F> where
F: FnMut(I::Item) -> B,
{
#[inline]
fn next_back(&mut self) -> Option<B> {
self.iter.next_back().map(&mut self.f)
}
}
/// An iterator that filters the elements of `iter` with `predicate`.
///
/// This `struct` is created by the [`filter()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`filter()`]: trait.Iterator.html#method.filter
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Filter<I, P> {
iter: I,
predicate: P,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, P> Iterator for Filter<I, P> where P: FnMut(&I::Item) -> bool {
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
for x in self.iter.by_ref() {
if (self.predicate)(&x) {
return Some(x);
}
}
None
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: DoubleEndedIterator, P> DoubleEndedIterator for Filter<I, P>
where P: FnMut(&I::Item) -> bool,
{
#[inline]
fn next_back(&mut self) -> Option<I::Item> {
for x in self.iter.by_ref().rev() {
if (self.predicate)(&x) {
return Some(x);
}
}
None
}
}
/// An iterator that uses `f` to both filter and map elements from `iter`.
///
/// This `struct` is created by the [`filter_map()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`filter_map()`]: trait.Iterator.html#method.filter_map
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct FilterMap<I, F> {
iter: I,
f: F,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: Iterator, F> Iterator for FilterMap<I, F>
where F: FnMut(I::Item) -> Option<B>,
{
type Item = B;
#[inline]
fn next(&mut self) -> Option<B> {
for x in self.iter.by_ref() {
if let Some(y) = (self.f)(x) {
return Some(y);
}
}
None
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for FilterMap<I, F>
where F: FnMut(I::Item) -> Option<B>,
{
#[inline]
fn next_back(&mut self) -> Option<B> {
for x in self.iter.by_ref().rev() {
if let Some(y) = (self.f)(x) {
return Some(y);
}
}
None
}
}
/// An iterator that yields the current count and the element during iteration.
///
/// This `struct` is created by the [`enumerate()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`enumerate()`]: trait.Iterator.html#method.enumerate
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Enumerate<I> {
iter: I,
count: usize,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Enumerate<I> where I: Iterator {
type Item = (usize, <I as Iterator>::Item);
/// # 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.
///
/// # Panics
///
/// Might panic if the index of the element overflows a `usize`.
#[inline]
fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
self.iter.next().map(|a| {
let ret = (self.count, a);
// Possible undefined overflow.
self.count += 1;
ret
})
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
#[inline]
fn nth(&mut self, n: usize) -> Option<(usize, I::Item)> {
self.iter.nth(n).map(|a| {
let i = self.count + n;
self.count = i + 1;
(i, a)
})
}
#[inline]
fn count(self) -> usize {
self.iter.count()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> DoubleEndedIterator for Enumerate<I> where
I: ExactSizeIterator + DoubleEndedIterator
{
#[inline]
fn next_back(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
self.iter.next_back().map(|a| {
let len = self.iter.len();
// Can safely add, `ExactSizeIterator` promises that the number of
// elements fits into a `usize`.
(self.count + len, a)
})
}
}
/// An iterator with a `peek()` that returns an optional reference to the next
/// element.
///
/// This `struct` is created by the [`peekable()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`peekable()`]: trait.Iterator.html#method.peekable
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Peekable<I: Iterator> {
iter: I,
peeked: Option<I::Item>,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator> Iterator for Peekable<I> {
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
match self.peeked {
Some(_) => self.peeked.take(),
None => self.iter.next(),
}
}
#[inline]
fn count(self) -> usize {
(if self.peeked.is_some() { 1 } else { 0 }) + self.iter.count()
}
#[inline]
fn nth(&mut self, n: usize) -> Option<I::Item> {
match self.peeked {
Some(_) if n == 0 => self.peeked.take(),
Some(_) => {
self.peeked = None;
self.iter.nth(n-1)
},
None => self.iter.nth(n)
}
}
#[inline]
fn last(self) -> Option<I::Item> {
self.iter.last().or(self.peeked)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (lo, hi) = self.iter.size_hint();
if self.peeked.is_some() {
let lo = lo.saturating_add(1);
let hi = hi.and_then(|x| x.checked_add(1));
(lo, hi)
} else {
(lo, hi)
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: ExactSizeIterator> ExactSizeIterator for Peekable<I> {}
impl<I: Iterator> Peekable<I> {
/// Returns a reference to the next() value without advancing the iterator.
///
/// The `peek()` method will return the value that a call to [`next()`] would
/// return, but does not advance the iterator. Like [`next()`], if there is
/// a value, it's wrapped in a `Some(T)`, but if the iterator is over, it
/// will return `None`.
///
/// [`next()`]: trait.Iterator.html#tymethod.next
///
/// Because `peek()` returns reference, and many iterators iterate over
/// references, this leads to a possibly confusing situation where the
/// return value is a double reference. You can see this effect in the
/// examples below, with `&&i32`.
///
/// # 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")]
pub fn peek(&mut self) -> Option<&I::Item> {
if self.peeked.is_none() {
self.peeked = self.iter.next();
}
match self.peeked {
Some(ref value) => Some(value),
None => None,
}
}
/// Checks if the iterator has finished iterating.
///
/// Returns `true` if there are no more elements in the iterator, and
/// `false` if there are.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(peekable_is_empty)]
///
/// let xs = [1, 2, 3];
///
/// let mut iter = xs.iter().peekable();
///
/// // there are still elements to iterate over
/// assert_eq!(iter.is_empty(), false);
///
/// // let's consume the iterator
/// iter.next();
/// iter.next();
/// iter.next();
///
/// assert_eq!(iter.is_empty(), true);
/// ```
#[unstable(feature = "peekable_is_empty", issue = "27701")]
#[inline]
pub fn is_empty(&mut self) -> bool {
self.peek().is_none()
}
}
/// An iterator that rejects elements while `predicate` is true.
///
/// This `struct` is created by the [`skip_while()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`skip_while()`]: trait.Iterator.html#method.skip_while
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct SkipWhile<I, P> {
iter: I,
flag: bool,
predicate: P,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, P> Iterator for SkipWhile<I, P>
where P: FnMut(&I::Item) -> bool
{
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
for x in self.iter.by_ref() {
if self.flag || !(self.predicate)(&x) {
self.flag = true;
return Some(x);
}
}
None
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
}
}
/// An iterator that only accepts elements while `predicate` is true.
///
/// This `struct` is created by the [`take_while()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`take_while()`]: trait.Iterator.html#method.take_while
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct TakeWhile<I, P> {
iter: I,
flag: bool,
predicate: P,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, P> Iterator for TakeWhile<I, P>
where P: FnMut(&I::Item) -> bool
{
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
if self.flag {
None
} else {
self.iter.next().and_then(|x| {
if (self.predicate)(&x) {
Some(x)
} else {
self.flag = true;
None
}
})
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
}
}
/// An iterator that skips over `n` elements of `iter`.
///
/// This `struct` is created by the [`skip()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`skip()`]: trait.Iterator.html#method.skip
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Skip<I> {
iter: I,
n: usize
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Skip<I> where I: Iterator {
type Item = <I as Iterator>::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
if self.n == 0 {
self.iter.next()
} else {
let old_n = self.n;
self.n = 0;
self.iter.nth(old_n)
}
}
#[inline]
fn nth(&mut self, n: usize) -> Option<I::Item> {
// Can't just add n + self.n due to overflow.
if self.n == 0 {
self.iter.nth(n)
} else {
let to_skip = self.n;
self.n = 0;
// nth(n) skips n+1
if self.iter.nth(to_skip-1).is_none() {
return None;
}
self.iter.nth(n)
}
}
#[inline]
fn count(self) -> usize {
self.iter.count().saturating_sub(self.n)
}
#[inline]
fn last(mut self) -> Option<I::Item> {
if self.n == 0 {
self.iter.last()
} else {
let next = self.next();
if next.is_some() {
// recurse. n should be 0.
self.last().or(next)
} else {
None
}
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (lower, upper) = self.iter.size_hint();
let lower = lower.saturating_sub(self.n);
let upper = upper.map(|x| x.saturating_sub(self.n));
(lower, upper)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Skip<I> where I: ExactSizeIterator {}
/// An iterator that only iterates over the first `n` iterations of `iter`.
///
/// This `struct` is created by the [`take()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`take()`]: trait.Iterator.html#method.take
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Take<I> {
iter: I,
n: usize
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Take<I> where I: Iterator{
type Item = <I as Iterator>::Item;
#[inline]
fn next(&mut self) -> Option<<I as Iterator>::Item> {
if self.n != 0 {
self.n -= 1;
self.iter.next()
} else {
None
}
}
#[inline]
fn nth(&mut self, n: usize) -> Option<I::Item> {
if self.n > n {
self.n -= n + 1;
self.iter.nth(n)
} else {
if self.n > 0 {
self.iter.nth(self.n - 1);
self.n = 0;
}
None
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (lower, upper) = self.iter.size_hint();
let lower = cmp::min(lower, self.n);
let upper = match upper {
Some(x) if x < self.n => Some(x),
_ => Some(self.n)
};
(lower, upper)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Take<I> where I: ExactSizeIterator {}
/// An iterator to maintain state while iterating another iterator.
///
/// This `struct` is created by the [`scan()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`scan()`]: trait.Iterator.html#method.scan
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Scan<I, St, F> {
iter: I,
f: F,
state: St,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I, St, F> Iterator for Scan<I, St, F> where
I: Iterator,
F: FnMut(&mut St, I::Item) -> Option<B>,
{
type Item = B;
#[inline]
fn next(&mut self) -> Option<B> {
self.iter.next().and_then(|a| (self.f)(&mut self.state, a))
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the scan function
}
}
/// An iterator that maps each element to an iterator, and yields the elements
/// of the produced iterators.
///
/// This `struct` is created by the [`flat_map()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`flat_map()`]: trait.Iterator.html#method.flat_map
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct FlatMap<I, U: IntoIterator, F> {
iter: I,
f: F,
frontiter: Option<U::IntoIter>,
backiter: Option<U::IntoIter>,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, U: IntoIterator, F> Iterator for FlatMap<I, U, F>
where F: FnMut(I::Item) -> U,
{
type Item = U::Item;
#[inline]
fn next(&mut self) -> Option<U::Item> {
loop {
if let Some(ref mut inner) = self.frontiter {
if let Some(x) = inner.by_ref().next() {
return Some(x)
}
}
match self.iter.next().map(&mut self.f) {
None => return self.backiter.as_mut().and_then(|it| it.next()),
next => self.frontiter = next.map(IntoIterator::into_iter),
}
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (flo, fhi) = self.frontiter.as_ref().map_or((0, Some(0)), |it| it.size_hint());
let (blo, bhi) = self.backiter.as_ref().map_or((0, Some(0)), |it| it.size_hint());
let lo = flo.saturating_add(blo);
match (self.iter.size_hint(), fhi, bhi) {
((0, Some(0)), Some(a), Some(b)) => (lo, a.checked_add(b)),
_ => (lo, None)
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: DoubleEndedIterator, U, F> DoubleEndedIterator for FlatMap<I, U, F> where
F: FnMut(I::Item) -> U,
U: IntoIterator,
U::IntoIter: DoubleEndedIterator
{
#[inline]
fn next_back(&mut self) -> Option<U::Item> {
loop {
if let Some(ref mut inner) = self.backiter {
if let Some(y) = inner.next_back() {
return Some(y)
}
}
match self.iter.next_back().map(&mut self.f) {
None => return self.frontiter.as_mut().and_then(|it| it.next_back()),
next => self.backiter = next.map(IntoIterator::into_iter),
}
}
}
}
/// An iterator that yields `None` forever after the underlying iterator
/// yields `None` once.
///
/// This `struct` is created by the [`fuse()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`fuse()`]: trait.Iterator.html#method.fuse
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Fuse<I> {
iter: I,
done: bool
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Fuse<I> where I: Iterator {
type Item = <I as Iterator>::Item;
#[inline]
fn next(&mut self) -> Option<<I as Iterator>::Item> {
if self.done {
None
} else {
let next = self.iter.next();
self.done = next.is_none();
next
}
}
#[inline]
fn nth(&mut self, n: usize) -> Option<I::Item> {
if self.done {
None
} else {
let nth = self.iter.nth(n);
self.done = nth.is_none();
nth
}
}
#[inline]
fn last(self) -> Option<I::Item> {
if self.done {
None
} else {
self.iter.last()
}
}
#[inline]
fn count(self) -> usize {
if self.done {
0
} else {
self.iter.count()
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
if self.done {
(0, Some(0))
} else {
self.iter.size_hint()
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> DoubleEndedIterator for Fuse<I> where I: DoubleEndedIterator {
#[inline]
fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
if self.done {
None
} else {
let next = self.iter.next_back();
self.done = next.is_none();
next
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Fuse<I> where I: ExactSizeIterator {}
/// An iterator that calls a function with a reference to each element before
/// yielding it.
///
/// This `struct` is created by the [`inspect()`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`inspect()`]: trait.Iterator.html#method.inspect
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Inspect<I, F> {
iter: I,
f: F,
}
impl<I: Iterator, F> Inspect<I, F> where F: FnMut(&I::Item) {
#[inline]
fn do_inspect(&mut self, elt: Option<I::Item>) -> Option<I::Item> {
if let Some(ref a) = elt {
(self.f)(a);
}
elt
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, F> Iterator for Inspect<I, F> where F: FnMut(&I::Item) {
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
let next = self.iter.next();
self.do_inspect(next)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: DoubleEndedIterator, F> DoubleEndedIterator for Inspect<I, F>
where F: FnMut(&I::Item),
{
#[inline]
fn next_back(&mut self) -> Option<I::Item> {
let next = self.iter.next_back();
self.do_inspect(next)
}
}
/// Objects that can be stepped over in both directions.
///
/// The `steps_between` function provides a way to efficiently compare
/// two `Step` objects.
#[unstable(feature = "step_trait",
reason = "likely to be replaced by finer-grained traits",
issue = "27741")]
pub trait Step: PartialOrd + Sized {
/// Steps `self` if possible.
fn step(&self, by: &Self) -> Option<Self>;
/// Returns the number of steps between two step objects. The count is
/// inclusive of `start` and exclusive of `end`.
///
/// Returns `None` if it is not possible to calculate `steps_between`
/// without overflow.
fn steps_between(start: &Self, end: &Self, by: &Self) -> Option<usize>;
}
macro_rules! step_impl_unsigned {
($($t:ty)*) => ($(
#[unstable(feature = "step_trait",
reason = "likely to be replaced by finer-grained traits",
issue = "27741")]
impl Step for $t {
#[inline]
fn step(&self, by: &$t) -> Option<$t> {
(*self).checked_add(*by)
}
#[inline]
#[allow(trivial_numeric_casts)]
fn steps_between(start: &$t, end: &$t, by: &$t) -> Option<usize> {
if *by == 0 { return None; }
if *start < *end {
// Note: We assume $t <= usize here
let diff = (*end - *start) as usize;
let by = *by as usize;
if diff % by > 0 {
Some(diff / by + 1)
} else {
Some(diff / by)
}
} else {
Some(0)
}
}
}
)*)
}
macro_rules! step_impl_signed {
($($t:ty)*) => ($(
#[unstable(feature = "step_trait",
reason = "likely to be replaced by finer-grained traits",
issue = "27741")]
impl Step for $t {
#[inline]
fn step(&self, by: &$t) -> Option<$t> {
(*self).checked_add(*by)
}
#[inline]
#[allow(trivial_numeric_casts)]
fn steps_between(start: &$t, end: &$t, by: &$t) -> Option<usize> {
if *by == 0 { return None; }
let diff: usize;
let by_u: usize;
if *by > 0 {
if *start >= *end {
return Some(0);
}
// Note: We assume $t <= isize here
// Use .wrapping_sub and cast to usize to compute the
// difference that may not fit inside the range of isize.
diff = (*end as isize).wrapping_sub(*start as isize) as usize;
by_u = *by as usize;
} else {
if *start <= *end {
return Some(0);
}
diff = (*start as isize).wrapping_sub(*end as isize) as usize;
by_u = (*by as isize).wrapping_mul(-1) as usize;
}
if diff % by_u > 0 {
Some(diff / by_u + 1)
} else {
Some(diff / by_u)
}
}
}
)*)
}
macro_rules! step_impl_no_between {
($($t:ty)*) => ($(
#[unstable(feature = "step_trait",
reason = "likely to be replaced by finer-grained traits",
issue = "27741")]
impl Step for $t {
#[inline]
fn step(&self, by: &$t) -> Option<$t> {
(*self).checked_add(*by)
}
#[inline]
fn steps_between(_a: &$t, _b: &$t, _by: &$t) -> Option<usize> {
None
}
}
)*)
}
step_impl_unsigned!(usize u8 u16 u32);
step_impl_signed!(isize i8 i16 i32);
#[cfg(target_pointer_width = "64")]
step_impl_unsigned!(u64);
#[cfg(target_pointer_width = "64")]
step_impl_signed!(i64);
// If the target pointer width is not 64-bits, we
// assume here that it is less than 64-bits.
#[cfg(not(target_pointer_width = "64"))]
step_impl_no_between!(u64 i64);
/// An adapter for stepping range iterators by a custom amount.
///
/// The resulting iterator handles overflow by stopping. The `A`
/// parameter is the type being iterated over, while `R` is the range
/// type (usually one of `std::ops::{Range, RangeFrom}`.
#[derive(Clone)]
#[unstable(feature = "step_by", reason = "recent addition",
issue = "27741")]
pub struct StepBy<A, R> {
step_by: A,
range: R,
}
impl<A: Step> RangeFrom<A> {
/// Creates an iterator starting at the same point, but stepping by
/// the given amount at each iteration.
///
/// # Examples
///
/// ```ignore
/// for i in (0u8..).step_by(2) {
/// println!("{}", i);
/// }
/// ```
///
/// This prints all even `u8` values.
#[unstable(feature = "step_by", reason = "recent addition",
issue = "27741")]
pub fn step_by(self, by: A) -> StepBy<A, Self> {
StepBy {
step_by: by,
range: self
}
}
}
impl<A: Step> ops::Range<A> {
/// Creates an iterator with the same range, but stepping by the
/// given amount at each iteration.
///
/// The resulting iterator handles overflow by stopping.
///
/// # Examples
///
/// ```
/// #![feature(step_by)]
///
/// for i in (0..10).step_by(2) {
/// println!("{}", i);
/// }
/// ```
///
/// This prints:
///
/// ```text
/// 0
/// 2
/// 4
/// 6
/// 8
/// ```
#[unstable(feature = "step_by", reason = "recent addition",
issue = "27741")]
pub fn step_by(self, by: A) -> StepBy<A, Self> {
StepBy {
step_by: by,
range: self
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A> Iterator for StepBy<A, RangeFrom<A>> where
A: Clone,
for<'a> &'a A: Add<&'a A, Output = A>
{
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> {
let mut n = &self.range.start + &self.step_by;
mem::swap(&mut n, &mut self.range.start);
Some(n)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
(usize::MAX, None) // Too bad we can't specify an infinite lower bound
}
}
/// An iterator over the range [start, stop]
#[derive(Clone)]
#[unstable(feature = "range_inclusive",
reason = "likely to be replaced by range notation and adapters",
issue = "27777")]
#[rustc_deprecated(since = "1.5.0", reason = "replaced with ... syntax")]
#[allow(deprecated)]
pub struct RangeInclusive<A> {
range: ops::Range<A>,
done: bool,
}
/// Returns an iterator over the range [start, stop].
#[inline]
#[unstable(feature = "range_inclusive",
reason = "likely to be replaced by range notation and adapters",
issue = "27777")]
#[rustc_deprecated(since = "1.5.0", reason = "replaced with ... syntax")]
#[allow(deprecated)]
pub fn range_inclusive<A>(start: A, stop: A) -> RangeInclusive<A>
where A: Step + One + Clone
{
RangeInclusive {
range: start..stop,
done: false,
}
}
#[unstable(feature = "range_inclusive",
reason = "likely to be replaced by range notation and adapters",
issue = "27777")]
#[rustc_deprecated(since = "1.5.0", reason = "replaced with ... syntax")]
#[allow(deprecated)]
impl<A> Iterator for RangeInclusive<A> where
A: PartialEq + Step + One + Clone,
for<'a> &'a A: Add<&'a A, Output = A>
{
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> {
self.range.next().or_else(|| {
if !self.done && self.range.start == self.range.end {
self.done = true;
Some(self.range.end.clone())
} else {
None
}
})
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (lo, hi) = self.range.size_hint();
if self.done {
(lo, hi)
} else {
let lo = lo.saturating_add(1);
let hi = hi.and_then(|x| x.checked_add(1));
(lo, hi)
}
}
}
#[unstable(feature = "range_inclusive",
reason = "likely to be replaced by range notation and adapters",
issue = "27777")]
#[rustc_deprecated(since = "1.5.0", reason = "replaced with ... syntax")]
#[allow(deprecated)]
impl<A> DoubleEndedIterator for RangeInclusive<A> where
A: PartialEq + Step + One + Clone,
for<'a> &'a A: Add<&'a A, Output = A>,
for<'a> &'a A: Sub<Output=A>
{
#[inline]
fn next_back(&mut self) -> Option<A> {
if self.range.end > self.range.start {
let result = self.range.end.clone();
self.range.end = &self.range.end - &A::one();
Some(result)
} else if !self.done && self.range.start == self.range.end {
self.done = true;
Some(self.range.end.clone())
} else {
None
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Step + Zero + Clone> Iterator for StepBy<A, ops::Range<A>> {
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> {
let rev = self.step_by < A::zero();
if (rev && self.range.start > self.range.end) ||
(!rev && self.range.start < self.range.end)
{
match self.range.start.step(&self.step_by) {
Some(mut n) => {
mem::swap(&mut self.range.start, &mut n);
Some(n)
},
None => {
let mut n = self.range.end.clone();
mem::swap(&mut self.range.start, &mut n);
Some(n)
}
}
} else {
None
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
match Step::steps_between(&self.range.start,
&self.range.end,
&self.step_by) {
Some(hint) => (hint, Some(hint)),
None => (0, None)
}
}
}
macro_rules! range_exact_iter_impl {
($($t:ty)*) => ($(
#[stable(feature = "rust1", since = "1.0.0")]
impl ExactSizeIterator for ops::Range<$t> { }
)*)
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Step + One> Iterator for ops::Range<A> where
for<'a> &'a A: Add<&'a A, Output = A>
{
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> {
if self.start < self.end {
let mut n = &self.start + &A::one();
mem::swap(&mut n, &mut self.start);
Some(n)
} else {
None
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
match Step::steps_between(&self.start, &self.end, &A::one()) {
Some(hint) => (hint, Some(hint)),
None => (0, None)
}
}
}
// Ranges of u64 and i64 are excluded because they cannot guarantee having
// a length <= usize::MAX, which is required by ExactSizeIterator.
range_exact_iter_impl!(usize u8 u16 u32 isize i8 i16 i32);
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Step + One + Clone> DoubleEndedIterator for ops::Range<A> where
for<'a> &'a A: Add<&'a A, Output = A>,
for<'a> &'a A: Sub<&'a A, Output = A>
{
#[inline]
fn next_back(&mut self) -> Option<A> {
if self.start < self.end {
self.end = &self.end - &A::one();
Some(self.end.clone())
} else {
None
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Step + One> Iterator for ops::RangeFrom<A> where
for<'a> &'a A: Add<&'a A, Output = A>
{
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> {
let mut n = &self.start + &A::one();
mem::swap(&mut n, &mut self.start);
Some(n)
}
}
/// An iterator that repeats an element endlessly.
///
/// This `struct` is created by the [`repeat()`] function. See its documentation for more.
///
/// [`repeat()`]: fn.repeat.html
#[derive(Clone)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Repeat<A> {
element: A
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Clone> Iterator for Repeat<A> {
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> { Some(self.element.clone()) }
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) { (usize::MAX, None) }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Clone> DoubleEndedIterator for Repeat<A> {
#[inline]
fn next_back(&mut self) -> Option<A> { Some(self.element.clone()) }
}
/// Creates a new iterator that endlessly repeats a single element.
///
/// The `repeat()` function repeats a single value over and over and over and
/// over and over and 🔁.
///
/// Infinite iterators like `repeat()` are often used with adapters like
/// [`take()`], in order to make them finite.
///
/// [`take()`]: trait.Iterator.html#method.take
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // the number four 4ever:
/// let mut fours = iter::repeat(4);
///
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
///
/// // yup, still four
/// assert_eq!(Some(4), fours.next());
/// ```
///
/// Going finite with [`take()`]:
///
/// ```
/// use std::iter;
///
/// // that last example was too many fours. Let's only have four fours.
/// let mut four_fours = iter::repeat(4).take(4);
///
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
///
/// // ... and now we're done
/// assert_eq!(None, four_fours.next());
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn repeat<T: Clone>(elt: T) -> Repeat<T> {
Repeat{element: elt}
}
/// An iterator that yields nothing.
///
/// This `struct` is created by the [`empty()`] function. See its documentation for more.
///
/// [`empty()`]: fn.empty.html
#[stable(feature = "iter_empty", since = "1.2.0")]
pub struct Empty<T>(marker::PhantomData<T>);
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> Iterator for Empty<T> {
type Item = T;
fn next(&mut self) -> Option<T> {
None
}
fn size_hint(&self) -> (usize, Option<usize>){
(0, Some(0))
}
}
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> DoubleEndedIterator for Empty<T> {
fn next_back(&mut self) -> Option<T> {
None
}
}
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> ExactSizeIterator for Empty<T> {
fn len(&self) -> usize {
0
}
}
// not #[derive] because that adds a Clone bound on T,
// which isn't necessary.
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> Clone for Empty<T> {
fn clone(&self) -> Empty<T> {
Empty(marker::PhantomData)
}
}
// not #[derive] because that adds a Default bound on T,
// which isn't necessary.
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> Default for Empty<T> {
fn default() -> Empty<T> {
Empty(marker::PhantomData)
}
}
/// Creates an iterator that yields nothing.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // this could have been an iterator over i32, but alas, it's just not.
/// let mut nope = iter::empty::<i32>();
///
/// assert_eq!(None, nope.next());
/// ```
#[stable(feature = "iter_empty", since = "1.2.0")]
pub fn empty<T>() -> Empty<T> {
Empty(marker::PhantomData)
}
/// An iterator that yields an element exactly once.
///
/// This `struct` is created by the [`once()`] function. See its documentation for more.
///
/// [`once()`]: fn.once.html
#[derive(Clone)]
#[stable(feature = "iter_once", since = "1.2.0")]
pub struct Once<T> {
inner: ::option::IntoIter<T>
}
#[stable(feature = "iter_once", since = "1.2.0")]
impl<T> Iterator for Once<T> {
type Item = T;
fn next(&mut self) -> Option<T> {
self.inner.next()
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.inner.size_hint()
}
}
#[stable(feature = "iter_once", since = "1.2.0")]
impl<T> DoubleEndedIterator for Once<T> {
fn next_back(&mut self) -> Option<T> {
self.inner.next_back()
}
}
#[stable(feature = "iter_once", since = "1.2.0")]
impl<T> ExactSizeIterator for Once<T> {
fn len(&self) -> usize {
self.inner.len()
}
}
/// Creates an iterator that yields an element exactly once.
///
/// This is commonly used to adapt a single value into a [`chain()`] of other
/// kinds of iteration. Maybe you have an iterator that covers almost
/// everything, but you need an extra special case. Maybe you have a function
/// which works on iterators, but you only need to process one value.
///
/// [`chain()`]: trait.Iterator.html#method.chain
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // one is the loneliest number
/// let mut one = iter::once(1);
///
/// assert_eq!(Some(1), one.next());
///
/// // just one, that's all we get
/// assert_eq!(None, one.next());
/// ```
///
/// Chaining together with another iterator. Let's say that we want to iterate
/// over each file of the `.foo` directory, but also a configuration file,
/// `.foorc`:
///
/// ```no_run
/// use std::iter;
/// use std::fs;
/// use std::path::PathBuf;
///
/// let dirs = fs::read_dir(".foo").unwrap();
///
/// // we need to convert from an iterator of DirEntry-s to an iterator of
/// // PathBufs, so we use map
/// let dirs = dirs.map(|file| file.unwrap().path());
///
/// // now, our iterator just for our config file
/// let config = iter::once(PathBuf::from(".foorc"));
///
/// // chain the two iterators together into one big iterator
/// let files = dirs.chain(config);
///
/// // this will give us all of the files in .foo as well as .foorc
/// for f in files {
/// println!("{:?}", f);
/// }
/// ```
#[stable(feature = "iter_once", since = "1.2.0")]
pub fn once<T>(value: T) -> Once<T> {
Once { inner: Some(value).into_iter() }
}