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fuchsia / third_party / rust / 20d43d03dd27568f609d621ce44673393e838892 / . / src / libcore / iter / traits / iterator.rs
blob: c09df3f7f22cbd8c650cf85a33a93fe5c77061ff [file] [log] [blame]
use crate::cmp::Ordering;
use crate::ops::{Add, Try};
use super::super::LoopState;
use super::super::{Chain, Cycle, Copied, Cloned, Enumerate, Filter, FilterMap, Fuse};
use super::super::{Flatten, FlatMap};
use super::super::{Inspect, Map, Peekable, Scan, Skip, SkipWhile, StepBy, Take, TakeWhile, Rev};
use super::super::{Zip, Sum, Product, FromIterator};
fn _assert_is_object_safe(_: &dyn 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(
on(
_Self="[std::ops::Range<Idx>; 1]",
label="if you meant to iterate between two values, remove the square brackets",
note="`[start..end]` is an array of one `Range`; you might have meant to have a `Range` \
without the brackets: `start..end`"
),
on(
_Self="[std::ops::RangeFrom<Idx>; 1]",
label="if you meant to iterate from a value onwards, remove the square brackets",
note="`[start..]` is an array of one `RangeFrom`; you might have meant to have a \
`RangeFrom` without the brackets: `start..`, keeping in mind that iterating over an \
unbounded iterator will run forever unless you `break` or `return` from within the \
loop"
),
on(
_Self="[std::ops::RangeTo<Idx>; 1]",
label="if you meant to iterate until a value, remove the square brackets and add a \
starting value",
note="`[..end]` is an array of one `RangeTo`; you might have meant to have a bounded \
`Range` without the brackets: `0..end`"
),
on(
_Self="[std::ops::RangeInclusive<Idx>; 1]",
label="if you meant to iterate between two values, remove the square brackets",
note="`[start..=end]` is an array of one `RangeInclusive`; you might have meant to have a \
`RangeInclusive` without the brackets: `start..=end`"
),
on(
_Self="[std::ops::RangeToInclusive<Idx>; 1]",
label="if you meant to iterate until a value (including it), remove the square brackets \
and add a starting value",
note="`[..=end]` is an array of one `RangeToInclusive`; you might have meant to have a \
bounded `RangeInclusive` without the brackets: `0..=end`"
),
on(
_Self="std::ops::RangeTo<Idx>",
label="if you meant to iterate until a value, add a starting value",
note="`..end` is a `RangeTo`, which cannot be iterated on; you might have meant to have a \
bounded `Range`: `0..end`"
),
on(
_Self="std::ops::RangeToInclusive<Idx>",
label="if you meant to iterate until a value (including it), add a starting value",
note="`..=end` is a `RangeToInclusive`, which cannot be iterated on; you might have meant \
to have a bounded `RangeInclusive`: `0..=end`"
),
on(
_Self="&str",
label="`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`"
),
on(
_Self="std::string::String",
label="`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`"
),
on(
_Self="[]",
label="borrow the array with `&` or call `.iter()` on it to iterate over it",
note="arrays are not iterators, but slices like the following are: `&[1, 2, 3]`"
),
on(
_Self="{integral}",
note="if you want to iterate between `start` until a value `end`, use the exclusive range \
syntax `start..end` or the inclusive range syntax `start..=end`"
),
label="`{Self}` is not an iterator",
message="`{Self}` is not an iterator"
)]
#[doc(spotlight)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
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.
///
/// [`None`]: ../../std/option/enum.Option.html#variant.None
/// [`Some(Item)`]: ../../std/option/enum.Option.html#variant.Some
///
/// # 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.
///
/// [`usize`]: ../../std/primitive.usize.html
/// [`Option`]: ../../std/option/enum.Option.html
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # 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 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
/// // and the maximum possible lower bound
/// let iter = 0..;
///
/// assert_eq!((usize::max_value(), None), iter.size_hint());
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn size_hint(&self) -> (usize, Option<usize>) { (0, None) }
/// Consumes the iterator, counting the number of iterations and returning it.
///
/// This method will evaluate the iterator until its [`next`] returns
/// [`None`]. Once [`None`] is encountered, `count()` returns the number of
/// times it called [`next`].
///
/// [`next`]: #tymethod.next
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # 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.
///
/// [`usize::MAX`]: ../../std/usize/constant.MAX.html
///
/// # 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 {
#[inline]
fn add1<T>(count: usize, _: T) -> usize {
// Might overflow.
Add::add(count, 1)
}
self.fold(0, add1)
}
/// 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.
///
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # 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 {
#[inline]
fn some<T>(_: Option<T>, x: T) -> Option<T> {
Some(x)
}
self.fold(None, some)
}
/// Returns the `n`th element of the iterator.
///
/// Like most indexing operations, the count starts from zero, so `nth(0)`
/// returns the first value, `nth(1)` the second, and so on.
///
/// Note that all preceding elements, as well as the returned element, will be
/// consumed from the iterator. That means that the preceding elements will be
/// discarded, and also that calling `nth(0)` multiple times on the same iterator
/// will return different elements.
///
/// `nth()` will return [`None`] if `n` is greater than or equal to the length of the
/// iterator.
///
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
/// assert_eq!(a.iter().nth(1), Some(&2));
/// ```
///
/// Calling `nth()` multiple times doesn't rewind the iterator:
///
/// ```
/// let a = [1, 2, 3];
///
/// let mut iter = a.iter();
///
/// assert_eq!(iter.nth(1), Some(&2));
/// assert_eq!(iter.nth(1), None);
/// ```
///
/// Returning `None` if there are less than `n + 1` elements:
///
/// ```
/// let a = [1, 2, 3];
/// assert_eq!(a.iter().nth(10), None);
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn nth(&mut self, mut n: usize) -> Option<Self::Item> {
for x in self {
if n == 0 { return Some(x) }
n -= 1;
}
None
}
/// Creates an iterator starting at the same point, but stepping by
/// the given amount at each iteration.
///
/// Note 1: The first element of the iterator will always be returned,
/// regardless of the step given.
///
/// Note 2: The time at which ignored elements are pulled is not fixed.
/// `StepBy` behaves like the sequence `next(), nth(step-1), nth(step-1), …`,
/// but is also free to behave like the sequence
/// `advance_n_and_return_first(step), advance_n_and_return_first(step), …`
/// Which way is used may change for some iterators for performance reasons.
/// The second way will advance the iterator earlier and may consume more items.
///
/// `advance_n_and_return_first` is the equivalent of:
/// ```
/// fn advance_n_and_return_first<I>(iter: &mut I, total_step: usize) -> Option<I::Item>
/// where
/// I: Iterator,
/// {
/// let next = iter.next();
/// if total_step > 1 {
/// iter.nth(total_step-2);
/// }
/// next
/// }
/// ```
///
/// # Panics
///
/// The method will panic if the given step is `0`.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [0, 1, 2, 3, 4, 5];
/// let mut iter = a.iter().step_by(2);
///
/// assert_eq!(iter.next(), Some(&0));
/// assert_eq!(iter.next(), Some(&2));
/// assert_eq!(iter.next(), Some(&4));
/// assert_eq!(iter.next(), None);
/// ```
#[inline]
#[stable(feature = "iterator_step_by", since = "1.28.0")]
fn step_by(self, step: usize) -> StepBy<Self> where Self: Sized {
StepBy::new(self, step)
}
/// 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::new(self, other.into_iter())
}
/// '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.
///
/// If either iterator returns [`None`], [`next`] from the zipped iterator
/// will return [`None`]. If the first iterator returns [`None`], `zip` will
/// short-circuit and `next` will not be called on the second iterator.
///
/// # 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
/// [`next`]: ../../std/iter/trait.Iterator.html#tymethod.next
/// [`None`]: ../../std/option/enum.Option.html#variant.None
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> where
Self: Sized, U: IntoIterator
{
Zip::new(self, other.into_iter())
}
/// Takes a closure and creates an iterator which calls that closure on each
/// element.
///
/// `map()` transforms one iterator into another, by means of its argument:
/// something that implements [`FnMut`]. It produces a new iterator which
/// calls this closure on each element of the original iterator.
///
/// If you are good at thinking in types, you can think of `map()` like this:
/// If you have an iterator that gives you elements of some type `A`, and
/// you want an iterator of some other type `B`, you can use `map()`,
/// passing a closure that takes an `A` and returns a `B`.
///
/// `map()` is conceptually similar to a [`for`] loop. However, as `map()` is
/// lazy, it is best used when you're already working with other iterators.
/// If you're doing some sort of looping for a side effect, it's considered
/// more idiomatic to use [`for`] than `map()`.
///
/// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for
/// [`FnMut`]: ../../std/ops/trait.FnMut.html
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
///
/// let mut iter = a.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::new(self, f)
}
/// Calls a closure on each element of an iterator.
///
/// This is equivalent to using a [`for`] loop on the iterator, although
/// `break` and `continue` are not possible from a closure. It's generally
/// more idiomatic to use a `for` loop, but `for_each` may be more legible
/// when processing items at the end of longer iterator chains. In some
/// cases `for_each` may also be faster than a loop, because it will use
/// internal iteration on adaptors like `Chain`.
///
/// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::sync::mpsc::channel;
///
/// let (tx, rx) = channel();
/// (0..5).map(|x| x * 2 + 1)
/// .for_each(move |x| tx.send(x).unwrap());
///
/// let v: Vec<_> = rx.iter().collect();
/// assert_eq!(v, vec![1, 3, 5, 7, 9]);
/// ```
///
/// For such a small example, a `for` loop may be cleaner, but `for_each`
/// might be preferable to keep a functional style with longer iterators:
///
/// ```
/// (0..5).flat_map(|x| x * 100 .. x * 110)
/// .enumerate()
/// .filter(|&(i, x)| (i + x) % 3 == 0)
/// .for_each(|(i, x)| println!("{}:{}", i, x));
/// ```
#[inline]
#[stable(feature = "iterator_for_each", since = "1.21.0")]
fn for_each<F>(self, f: F) where
Self: Sized, F: FnMut(Self::Item),
{
#[inline]
fn call<T>(mut f: impl FnMut(T)) -> impl FnMut((), T) {
move |(), item| f(item)
}
self.fold((), call(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.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.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.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.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::new(self, 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)`][`Some`], 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`].
///
/// Why `filter_map` and not just [`filter`] and [`map`]? The key is in this
/// part:
///
/// [`filter`]: #method.filter
/// [`map`]: #method.map
///
/// > If the closure returns [`Some(element)`][`Some`], 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", "lol", "3", "NaN", "5"];
///
/// let mut iter = a.iter().filter_map(|s| s.parse().ok());
///
/// assert_eq!(iter.next(), Some(1));
/// assert_eq!(iter.next(), Some(3));
/// assert_eq!(iter.next(), Some(5));
/// assert_eq!(iter.next(), None);
/// ```
///
/// Here's the same example, but with [`filter`] and [`map`]:
///
/// ```
/// let a = ["1", "lol", "3", "NaN", "5"];
/// let mut iter = a.iter().map(|s| s.parse()).filter(|s| s.is_ok()).map(|s| s.unwrap());
/// assert_eq!(iter.next(), Some(1));
/// assert_eq!(iter.next(), Some(3));
/// assert_eq!(iter.next(), Some(5));
/// assert_eq!(iter.next(), None);
/// ```
///
/// [`Option<T>`]: ../../std/option/enum.Option.html
/// [`Some`]: ../../std/option/enum.Option.html#variant.Some
/// [`None`]: ../../std/option/enum.Option.html#variant.None
#[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::new(self, 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.
///
/// # 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
///
/// The returned iterator might panic if the to-be-returned index would
/// overflow a [`usize`].
///
/// [`usize::MAX`]: ../../std/usize/constant.MAX.html
/// [`usize`]: ../../std/primitive.usize.html
/// [`zip`]: #method.zip
///
/// # Examples
///
/// ```
/// let a = ['a', 'b', 'c'];
///
/// let mut iter = a.iter().enumerate();
///
/// assert_eq!(iter.next(), Some((0, &'a')));
/// assert_eq!(iter.next(), Some((1, &'b')));
/// assert_eq!(iter.next(), Some((2, &'c')));
/// assert_eq!(iter.next(), None);
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn enumerate(self) -> Enumerate<Self> where Self: Sized {
Enumerate::new(self)
}
/// Creates an iterator which can use `peek` to look at the next element of
/// the iterator without consuming it.
///
/// Adds a [`peek`] method to an iterator. See its documentation for
/// more information.
///
/// Note that the underlying iterator is still advanced when [`peek`] is
/// called for the first time: In order to retrieve the next element,
/// [`next`] is called on the underlying iterator, hence any side effects (i.e.
/// anything other than fetching the next value) of the [`next`] method
/// will occur.
///
/// [`peek`]: struct.Peekable.html#method.peek
/// [`next`]: ../../std/iter/trait.Iterator.html#tymethod.next
///
/// # 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::new(self)
}
/// 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.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.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.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::new(self, 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.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.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.iter().take_while(|x| **x < 0);
///
/// assert_eq!(iter.next(), Some(&-1));
///
/// // We have more elements that are less than zero, but since we already
/// // got a false, take_while() isn't used any more
/// assert_eq!(iter.next(), None);
/// ```
///
/// Because `take_while()` needs to look at the value in order to see if it
/// should be included or not, consuming iterators will see that it is
/// removed:
///
/// ```
/// let a = [1, 2, 3, 4];
/// let mut iter = a.iter();
///
/// let result: Vec<i32> = iter.by_ref()
/// .take_while(|n| **n != 3)
/// .cloned()
/// .collect();
///
/// assert_eq!(result, &[1, 2]);
///
/// let result: Vec<i32> = iter.cloned().collect();
///
/// assert_eq!(result, &[4]);
/// ```
///
/// The `3` is no longer there, because it was consumed in order to see if
/// the iteration should stop, but wasn't placed back into the iterator.
#[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::new(self, predicate)
}
/// Creates an iterator that skips the first `n` elements.
///
/// After they have been consumed, the rest of the elements are yielded.
/// Rather than overriding this method directly, instead override the `nth` method.
///
/// # 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::new(self, 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::new(self, n)
}
/// An iterator adaptor similar to [`fold`] that holds internal state and
/// produces a new iterator.
///
/// [`fold`]: #method.fold
///
/// `scan()` takes two arguments: an initial value which seeds the internal
/// state, and a closure with two arguments, the first being a mutable
/// reference to the internal state and the second an iterator element.
/// The closure can assign to the internal state to share state between
/// iterations.
///
/// On iteration, the closure will be applied to each element of the
/// iterator and the return value from the closure, an [`Option`], is
/// yielded by the iterator.
///
/// [`Option`]: ../../std/option/enum.Option.html
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
///
/// let mut iter = a.iter().scan(1, |state, &x| {
/// // each iteration, we'll multiply the state by the element
/// *state = *state * x;
///
/// // then, we'll yield the negation of the state
/// 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::new(self, initial_state, f)
}
/// 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.
///
/// You can think of `flat_map(f)` as the semantic equivalent
/// of [`map`]ping, and then [`flatten`]ing as in `map(f).flatten()`.
///
/// 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.
///
/// [`map`]: #method.map
/// [`flatten`]: #method.flatten
///
/// # 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::new(self, f)
}
/// Creates an iterator that flattens nested structure.
///
/// This is useful when you have an iterator of iterators or an iterator of
/// things that can be turned into iterators and you want to remove one
/// level of indirection.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let data = vec![vec![1, 2, 3, 4], vec![5, 6]];
/// let flattened = data.into_iter().flatten().collect::<Vec<u8>>();
/// assert_eq!(flattened, &[1, 2, 3, 4, 5, 6]);
/// ```
///
/// Mapping and then flattening:
///
/// ```
/// let words = ["alpha", "beta", "gamma"];
///
/// // chars() returns an iterator
/// let merged: String = words.iter()
/// .map(|s| s.chars())
/// .flatten()
/// .collect();
/// assert_eq!(merged, "alphabetagamma");
/// ```
///
/// You can also rewrite this in terms of [`flat_map()`], which is preferable
/// in this case since it conveys intent more clearly:
///
/// ```
/// let words = ["alpha", "beta", "gamma"];
///
/// // chars() returns an iterator
/// let merged: String = words.iter()
/// .flat_map(|s| s.chars())
/// .collect();
/// assert_eq!(merged, "alphabetagamma");
/// ```
///
/// Flattening once only removes one level of nesting:
///
/// ```
/// let d3 = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]];
///
/// let d2 = d3.iter().flatten().collect::<Vec<_>>();
/// assert_eq!(d2, [&[1, 2], &[3, 4], &[5, 6], &[7, 8]]);
///
/// let d1 = d3.iter().flatten().flatten().collect::<Vec<_>>();
/// assert_eq!(d1, [&1, &2, &3, &4, &5, &6, &7, &8]);
/// ```
///
/// Here we see that `flatten()` does not perform a "deep" flatten.
/// Instead, only one level of nesting is removed. That is, if you
/// `flatten()` a three-dimensional array the result will be
/// two-dimensional and not one-dimensional. To get a one-dimensional
/// structure, you have to `flatten()` again.
///
/// [`flat_map()`]: #method.flat_map
#[inline]
#[stable(feature = "iterator_flatten", since = "1.29.0")]
fn flatten(self) -> Flatten<Self>
where Self: Sized, Self::Item: IntoIterator {
Flatten::new(self)
}
/// 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.
///
/// [`None`]: ../../std/option/enum.Option.html#variant.None
/// [`Some(T)`]: ../../std/option/enum.Option.html#variant.Some
///
/// # 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::new(self)
}
/// 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 more common for `inspect()` to be used as a debugging tool than to
/// exist in your final code, but applications may find it useful in certain
/// situations when errors need to be logged before being discarded.
///
/// # 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
/// 6
/// 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
/// ```
///
/// Logging errors before discarding them:
///
/// ```
/// let lines = ["1", "2", "a"];
///
/// let sum: i32 = lines
/// .iter()
/// .map(|line| line.parse::<i32>())
/// .inspect(|num| {
/// if let Err(ref e) = *num {
/// println!("Parsing error: {}", e);
/// }
/// })
/// .filter_map(Result::ok)
/// .sum();
///
/// println!("Sum: {}", sum);
/// ```
///
/// This will print:
///
/// ```text
/// Parsing error: invalid digit found in string
/// Sum: 3
/// ```
#[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::new(self, 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.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.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>`][`Result`] can be thought of as single
/// [`Result`]`<Collection<T>, E>`. See the examples below for more.
///
/// Because `collect()` is so general, it can cause problems with type
/// inference. As such, `collect()` is one of the few times you'll see
/// the syntax affectionately known as the 'turbofish': `::<>`. This
/// helps the inference algorithm understand specifically which collection
/// you're trying to collect into.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
///
/// let doubled: Vec<i32> = a.iter()
/// .map(|&x| x * 2)
/// .collect();
///
/// assert_eq!(vec![2, 4, 6], doubled);
/// ```
///
/// Note that we needed the `: Vec<i32>` on the left-hand side. This is because
/// we could collect into, for example, a [`VecDeque<T>`] instead:
///
/// [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html
///
/// ```
/// use std::collections::VecDeque;
///
/// let a = [1, 2, 3];
///
/// let doubled: VecDeque<i32> = a.iter().map(|&x| x * 2).collect();
///
/// assert_eq!(2, doubled[0]);
/// assert_eq!(4, doubled[1]);
/// assert_eq!(6, doubled[2]);
/// ```
///
/// Using the 'turbofish' instead of annotating `doubled`:
///
/// ```
/// let a = [1, 2, 3];
///
/// let doubled = a.iter().map(|x| x * 2).collect::<Vec<i32>>();
///
/// assert_eq!(vec![2, 4, 6], doubled);
/// ```
///
/// Because `collect()` only 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>`][`Result`]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);
/// ```
///
/// [`iter`]: ../../std/iter/trait.Iterator.html#tymethod.next
/// [`String`]: ../../std/string/struct.String.html
/// [`char`]: ../../std/primitive.char.html
/// [`Result`]: ../../std/result/enum.Result.html
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"]
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`.
///
/// See also [`is_partitioned()`] and [`partition_in_place()`].
///
/// [`is_partitioned()`]: #method.is_partitioned
/// [`partition_in_place()`]: #method.partition_in_place
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
///
/// let (even, odd): (Vec<i32>, Vec<i32>) = a
/// .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, f: F) -> (B, B) where
Self: Sized,
B: Default + Extend<Self::Item>,
F: FnMut(&Self::Item) -> bool
{
#[inline]
fn extend<'a, T, B: Extend<T>>(
mut f: impl FnMut(&T) -> bool + 'a,
left: &'a mut B,
right: &'a mut B,
) -> impl FnMut(T) + 'a {
move |x| {
if f(&x) {
left.extend(Some(x));
} else {
right.extend(Some(x));
}
}
}
let mut left: B = Default::default();
let mut right: B = Default::default();
self.for_each(extend(f, &mut left, &mut right));
(left, right)
}
/// Reorder the elements of this iterator *in-place* according to the given predicate,
/// such that all those that return `true` precede all those that return `false`.
/// Returns the number of `true` elements found.
///
/// The relative order of partitioned items is not maintained.
///
/// See also [`is_partitioned()`] and [`partition()`].
///
/// [`is_partitioned()`]: #method.is_partitioned
/// [`partition()`]: #method.partition
///
/// # Examples
///
/// ```
/// #![feature(iter_partition_in_place)]
///
/// let mut a = [1, 2, 3, 4, 5, 6, 7];
///
/// // Partition in-place between evens and odds
/// let i = a.iter_mut().partition_in_place(|&n| n % 2 == 0);
///
/// assert_eq!(i, 3);
/// assert!(a[..i].iter().all(|&n| n % 2 == 0)); // evens
/// assert!(a[i..].iter().all(|&n| n % 2 == 1)); // odds
/// ```
#[unstable(feature = "iter_partition_in_place", reason = "new API", issue = "62543")]
fn partition_in_place<'a, T: 'a, P>(mut self, ref mut predicate: P) -> usize
where
Self: Sized + DoubleEndedIterator<Item = &'a mut T>,
P: FnMut(&T) -> bool,
{
// FIXME: should we worry about the count overflowing? The only way to have more than
// `usize::MAX` mutable references is with ZSTs, which aren't useful to partition...
// These closure "factory" functions exist to avoid genericity in `Self`.
#[inline]
fn is_false<'a, T>(
predicate: &'a mut impl FnMut(&T) -> bool,
true_count: &'a mut usize,
) -> impl FnMut(&&mut T) -> bool + 'a {
move |x| {
let p = predicate(&**x);
*true_count += p as usize;
!p
}
}
#[inline]
fn is_true<T>(
predicate: &mut impl FnMut(&T) -> bool
) -> impl FnMut(&&mut T) -> bool + '_ {
move |x| predicate(&**x)
}
// Repeatedly find the first `false` and swap it with the last `true`.
let mut true_count = 0;
while let Some(head) = self.find(is_false(predicate, &mut true_count)) {
if let Some(tail) = self.rfind(is_true(predicate)) {
crate::mem::swap(head, tail);
true_count += 1;
} else {
break;
}
}
true_count
}
/// Checks if the elements of this iterator are partitioned according to the given predicate,
/// such that all those that return `true` precede all those that return `false`.
///
/// See also [`partition()`] and [`partition_in_place()`].
///
/// [`partition()`]: #method.partition
/// [`partition_in_place()`]: #method.partition_in_place
///
/// # Examples
///
/// ```
/// #![feature(iter_is_partitioned)]
///
/// assert!("Iterator".chars().is_partitioned(char::is_uppercase));
/// assert!(!"IntoIterator".chars().is_partitioned(char::is_uppercase));
/// ```
#[unstable(feature = "iter_is_partitioned", reason = "new API", issue = "62544")]
fn is_partitioned<P>(mut self, mut predicate: P) -> bool
where
Self: Sized,
P: FnMut(Self::Item) -> bool,
{
// Either all items test `true`, or the first clause stops at `false`
// and we check that there are no more `true` items after that.
self.all(&mut predicate) || !self.any(predicate)
}
/// An iterator method that applies a function as long as it returns
/// successfully, producing a single, final value.
///
/// `try_fold()` takes two arguments: an initial value, and a closure with
/// two arguments: an 'accumulator', and an element. The closure either
/// returns successfully, with the value that the accumulator should have
/// for the next iteration, or it returns failure, with an error value that
/// is propagated back to the caller immediately (short-circuiting).
///
/// The initial value is the value the accumulator will have on the first
/// call. If applying the closure succeeded against every element of the
/// iterator, `try_fold()` returns the final accumulator as success.
///
/// Folding is useful whenever you have a collection of something, and want
/// to produce a single value from it.
///
/// # Note to Implementors
///
/// Most of the other (forward) methods have default implementations in
/// terms of this one, so try to implement this explicitly if it can
/// do something better than the default `for` loop implementation.
///
/// In particular, try to have this call `try_fold()` on the internal parts
/// from which this iterator is composed. If multiple calls are needed,
/// the `?` operator may be convenient for chaining the accumulator value
/// along, but beware any invariants that need to be upheld before those
/// early returns. This is a `&mut self` method, so iteration needs to be
/// resumable after hitting an error here.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
///
/// // the checked sum of all of the elements of the array
/// let sum = a.iter().try_fold(0i8, |acc, &x| acc.checked_add(x));
///
/// assert_eq!(sum, Some(6));
/// ```
///
/// Short-circuiting:
///
/// ```
/// let a = [10, 20, 30, 100, 40, 50];
/// let mut it = a.iter();
///
/// // This sum overflows when adding the 100 element
/// let sum = it.try_fold(0i8, |acc, &x| acc.checked_add(x));
/// assert_eq!(sum, None);
///
/// // Because it short-circuited, the remaining elements are still
/// // available through the iterator.
/// assert_eq!(it.len(), 2);
/// assert_eq!(it.next(), Some(&40));
/// ```
#[inline]
#[stable(feature = "iterator_try_fold", since = "1.27.0")]
fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R where
Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
{
let mut accum = init;
while let Some(x) = self.next() {
accum = f(accum, x)?;
}
Try::from_ok(accum)
}
/// An iterator method that applies a fallible function to each item in the
/// iterator, stopping at the first error and returning that error.
///
/// This can also be thought of as the fallible form of [`for_each()`]
/// or as the stateless version of [`try_fold()`].
///
/// [`for_each()`]: #method.for_each
/// [`try_fold()`]: #method.try_fold
///
/// # Examples
///
/// ```
/// use std::fs::rename;
/// use std::io::{stdout, Write};
/// use std::path::Path;
///
/// let data = ["no_tea.txt", "stale_bread.json", "torrential_rain.png"];
///
/// let res = data.iter().try_for_each(|x| writeln!(stdout(), "{}", x));
/// assert!(res.is_ok());
///
/// let mut it = data.iter().cloned();
/// let res = it.try_for_each(|x| rename(x, Path::new(x).with_extension("old")));
/// assert!(res.is_err());
/// // It short-circuited, so the remaining items are still in the iterator:
/// assert_eq!(it.next(), Some("stale_bread.json"));
/// ```
#[inline]
#[stable(feature = "iterator_try_fold", since = "1.27.0")]
fn try_for_each<F, R>(&mut self, f: F) -> R where
Self: Sized, F: FnMut(Self::Item) -> R, R: Try<Ok=()>
{
#[inline]
fn call<T, R>(mut f: impl FnMut(T) -> R) -> impl FnMut((), T) -> R {
move |(), x| f(x)
}
self.try_fold((), call(f))
}
/// An iterator method that applies a function, producing a single, final value.
///
/// `fold()` takes two arguments: an initial value, and a closure with two
/// arguments: an 'accumulator', and an element. The closure returns the value that
/// the accumulator should have for the next iteration.
///
/// The initial value is the value the accumulator will have on the first
/// call.
///
/// After applying this closure to every element of the iterator, `fold()`
/// returns the accumulator.
///
/// This operation is sometimes called 'reduce' or 'inject'.
///
/// Folding is useful whenever you have a collection of something, and want
/// to produce a single value from it.
///
/// Note: `fold()`, and similar methods that traverse the entire iterator,
/// may not terminate for infinite iterators, even on traits for which a
/// result is determinable in finite time.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
///
/// // the sum of all of the elements of the array
/// 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:
///
/// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for
///
/// ```
/// 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>(mut self, init: B, f: F) -> B where
Self: Sized, F: FnMut(B, Self::Item) -> B,
{
#[inline]
fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
move |acc, x| Ok(f(acc, x))
}
self.try_fold(init, ok(f)).unwrap()
}
/// Tests if every element of the iterator matches a predicate.
///
/// `all()` takes a closure that returns `true` or `false`. It applies
/// this closure to each element of the iterator, and if they all return
/// `true`, then so does `all()`. If any of them return `false`, it
/// returns `false`.
///
/// `all()` is short-circuiting; in other words, it will stop processing
/// as soon as it finds a `false`, given that no matter what else happens,
/// the result will also be `false`.
///
/// An empty iterator returns `true`.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
///
/// assert!(a.iter().all(|&x| x > 0));
///
/// assert!(!a.iter().all(|&x| x > 2));
/// ```
///
/// Stopping at the first `false`:
///
/// ```
/// let a = [1, 2, 3];
///
/// let mut iter = a.iter();
///
/// assert!(!iter.all(|&x| x != 2));
///
/// // we can still use `iter`, as there are more elements.
/// assert_eq!(iter.next(), Some(&3));
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn all<F>(&mut self, f: F) -> bool where
Self: Sized, F: FnMut(Self::Item) -> bool
{
#[inline]
fn check<T>(mut f: impl FnMut(T) -> bool) -> impl FnMut(T) -> LoopState<(), ()> {
move |x| {
if f(x) { LoopState::Continue(()) }
else { LoopState::Break(()) }
}
}
self.try_for_each(check(f)) == LoopState::Continue(())
}
/// Tests if any element of the iterator matches a predicate.
///
/// `any()` takes a closure that returns `true` or `false`. It applies
/// this closure to each element of the iterator, and if any of them return
/// `true`, then so does `any()`. If they all return `false`, it
/// returns `false`.
///
/// `any()` is short-circuiting; in other words, it will stop processing
/// as soon as it finds a `true`, given that no matter what else happens,
/// the result will also be `true`.
///
/// An empty iterator returns `false`.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
///
/// assert!(a.iter().any(|&x| x > 0));
///
/// assert!(!a.iter().any(|&x| x > 5));
/// ```
///
/// Stopping at the first `true`:
///
/// ```
/// let a = [1, 2, 3];
///
/// let mut iter = a.iter();
///
/// assert!(iter.any(|&x| x != 2));
///
/// // we can still use `iter`, as there are more elements.
/// assert_eq!(iter.next(), Some(&2));
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn any<F>(&mut self, f: F) -> bool where
Self: Sized,
F: FnMut(Self::Item) -> bool
{
#[inline]
fn check<T>(mut f: impl FnMut(T) -> bool) -> impl FnMut(T) -> LoopState<(), ()> {
move |x| {
if f(x) { LoopState::Break(()) }
else { LoopState::Continue(()) }
}
}
self.try_for_each(check(f)) == LoopState::Break(())
}
/// Searches for an element of an iterator that satisfies a predicate.
///
/// `find()` takes a closure that returns `true` or `false`. It applies
/// this closure to each element of the iterator, and if any of them return
/// `true`, then `find()` returns [`Some(element)`]. If they all return
/// `false`, it returns [`None`].
///
/// `find()` is short-circuiting; in other words, it will stop processing
/// as soon as the closure returns `true`.
///
/// Because `find()` takes a reference, and many iterators iterate over
/// references, this leads to a possibly confusing situation where the
/// argument is a double reference. You can see this effect in the
/// examples below, with `&&x`.
///
/// [`Some(element)`]: ../../std/option/enum.Option.html#variant.Some
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # 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, predicate: P) -> Option<Self::Item> where
Self: Sized,
P: FnMut(&Self::Item) -> bool,
{
#[inline]
fn check<T>(mut predicate: impl FnMut(&T) -> bool) -> impl FnMut(T) -> LoopState<(), T> {
move |x| {
if predicate(&x) { LoopState::Break(x) }
else { LoopState::Continue(()) }
}
}
self.try_for_each(check(predicate)).break_value()
}
/// Applies function to the elements of iterator and returns
/// the first non-none result.
///
/// `iter.find_map(f)` is equivalent to `iter.filter_map(f).next()`.
///
///
/// # Examples
///
/// ```
/// let a = ["lol", "NaN", "2", "5"];
///
/// let first_number = a.iter().find_map(|s| s.parse().ok());
///
/// assert_eq!(first_number, Some(2));
/// ```
#[inline]
#[stable(feature = "iterator_find_map", since = "1.30.0")]
fn find_map<B, F>(&mut self, f: F) -> Option<B> where
Self: Sized,
F: FnMut(Self::Item) -> Option<B>,
{
#[inline]
fn check<T, B>(mut f: impl FnMut(T) -> Option<B>) -> impl FnMut(T) -> LoopState<(), B> {
move |x| match f(x) {
Some(x) => LoopState::Break(x),
None => LoopState::Continue(()),
}
}
self.try_for_each(check(f)).break_value()
}
/// Searches for an element in an iterator, returning its index.
///
/// `position()` takes a closure that returns `true` or `false`. It applies
/// this closure to each element of the iterator, and if one of them
/// returns `true`, then `position()` returns [`Some(index)`]. If all of
/// them return `false`, it returns [`None`].
///
/// `position()` is short-circuiting; in other words, it will stop
/// processing as soon as it finds a `true`.
///
/// # Overflow Behavior
///
/// The method does no guarding against overflows, so if there are more
/// than [`usize::MAX`] non-matching elements, it either produces the wrong
/// result or panics. If debug assertions are enabled, a panic is
/// guaranteed.
///
/// # Panics
///
/// This function might panic if the iterator has more than `usize::MAX`
/// non-matching elements.
///
/// [`Some(index)`]: ../../std/option/enum.Option.html#variant.Some
/// [`None`]: ../../std/option/enum.Option.html#variant.None
/// [`usize::MAX`]: ../../std/usize/constant.MAX.html
///
/// # 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, 4];
///
/// 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));
///
/// // The returned index depends on iterator state
/// assert_eq!(iter.position(|&x| x == 4), Some(0));
///
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn position<P>(&mut self, predicate: P) -> Option<usize> where
Self: Sized,
P: FnMut(Self::Item) -> bool,
{
#[inline]
fn check<T>(
mut predicate: impl FnMut(T) -> bool,
) -> impl FnMut(usize, T) -> LoopState<usize, usize> {
// The addition might panic on overflow
move |i, x| {
if predicate(x) { LoopState::Break(i) }
else { LoopState::Continue(Add::add(i, 1)) }
}
}
self.try_fold(0, check(predicate)).break_value()
}
/// Searches for an element in an iterator from the right, returning its
/// index.
///
/// `rposition()` takes a closure that returns `true` or `false`. It applies
/// this closure to each element of the iterator, starting from the end,
/// and if one of them returns `true`, then `rposition()` returns
/// [`Some(index)`]. If all of them return `false`, it returns [`None`].
///
/// `rposition()` is short-circuiting; in other words, it will stop
/// processing as soon as it finds a `true`.
///
/// [`Some(index)`]: ../../std/option/enum.Option.html#variant.Some
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # 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, predicate: P) -> Option<usize> where
P: FnMut(Self::Item) -> bool,
Self: Sized + ExactSizeIterator + DoubleEndedIterator
{
// No need for an overflow check here, because `ExactSizeIterator`
// implies that the number of elements fits into a `usize`.
#[inline]
fn check<T>(
mut predicate: impl FnMut(T) -> bool,
) -> impl FnMut(usize, T) -> LoopState<usize, usize> {
move |i, x| {
let i = i - 1;
if predicate(x) { LoopState::Break(i) }
else { LoopState::Continue(i) }
}
}
let n = self.len();
self.try_rfold(n, check(predicate)).break_value()
}
/// Returns the maximum element of an iterator.
///
/// If several elements are equally maximum, the last element is
/// returned. If the iterator is empty, [`None`] is returned.
///
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
/// let b: Vec<u32> = Vec::new();
///
/// assert_eq!(a.iter().max(), Some(&3));
/// assert_eq!(b.iter().max(), None);
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn max(self) -> Option<Self::Item> where Self: Sized, Self::Item: Ord
{
self.max_by(Ord::cmp)
}
/// Returns the minimum element of an iterator.
///
/// If several elements are equally minimum, the first element is
/// returned. If the iterator is empty, [`None`] is returned.
///
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
/// let b: Vec<u32> = Vec::new();
///
/// assert_eq!(a.iter().min(), Some(&1));
/// assert_eq!(b.iter().min(), None);
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn min(self) -> Option<Self::Item> where Self: Sized, Self::Item: Ord
{
self.min_by(Ord::cmp)
}
/// Returns the element that gives the maximum value from the
/// specified function.
///
/// If several elements are equally maximum, the last element is
/// returned. If the iterator is empty, [`None`] is returned.
///
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # 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,
{
#[inline]
fn key<T, B>(mut f: impl FnMut(&T) -> B) -> impl FnMut(T) -> (B, T) {
move |x| (f(&x), x)
}
// switch to y even if it is only equal, to preserve stability.
#[inline]
fn select<T, B: Ord>((x_p, _): &(B, T), (y_p, _): &(B, T)) -> bool {
x_p <= y_p
}
let (_, x) = select_fold1(self.map(key(f)), select)?;
Some(x)
}
/// Returns the element that gives the maximum value with respect to the
/// specified comparison function.
///
/// If several elements are equally maximum, the last element is
/// returned. If the iterator is empty, [`None`] is returned.
///
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # Examples
///
/// ```
/// let a = [-3_i32, 0, 1, 5, -10];
/// assert_eq!(*a.iter().max_by(|x, y| x.cmp(y)).unwrap(), 5);
/// ```
#[inline]
#[stable(feature = "iter_max_by", since = "1.15.0")]
fn max_by<F>(self, compare: F) -> Option<Self::Item>
where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,
{
// switch to y even if it is only equal, to preserve stability.
#[inline]
fn select<T>(mut compare: impl FnMut(&T, &T) -> Ordering) -> impl FnMut(&T, &T) -> bool {
move |x, y| compare(x, y) != Ordering::Greater
}
select_fold1(self, select(compare))
}
/// Returns the element that gives the minimum value from the
/// specified function.
///
/// If several elements are equally minimum, the first element is
/// returned. If the iterator is empty, [`None`] is returned.
///
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # Examples
///
/// ```
/// let a = [-3_i32, 0, 1, 5, -10];
/// assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0);
/// ```
#[inline]
#[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,
{
#[inline]
fn key<T, B>(mut f: impl FnMut(&T) -> B) -> impl FnMut(T) -> (B, T) {
move |x| (f(&x), x)
}
// only switch to y if it is strictly smaller, to preserve stability.
#[inline]
fn select<T, B: Ord>((x_p, _): &(B, T), (y_p, _): &(B, T)) -> bool {
x_p > y_p
}
let (_, x) = select_fold1(self.map(key(f)), select)?;
Some(x)
}
/// Returns the element that gives the minimum value with respect to the
/// specified comparison function.
///
/// If several elements are equally minimum, the first element is
/// returned. If the iterator is empty, [`None`] is returned.
///
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # Examples
///
/// ```
/// let a = [-3_i32, 0, 1, 5, -10];
/// assert_eq!(*a.iter().min_by(|x, y| x.cmp(y)).unwrap(), -10);
/// ```
#[inline]
#[stable(feature = "iter_min_by", since = "1.15.0")]
fn min_by<F>(self, compare: F) -> Option<Self::Item>
where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,
{
// only switch to y if it is strictly smaller, to preserve stability.
#[inline]
fn select<T>(mut compare: impl FnMut(&T, &T) -> Ordering) -> impl FnMut(&T, &T) -> bool {
move |x, y| compare(x, y) == Ordering::Greater
}
select_fold1(self, select(compare))
}
/// 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::new(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)>,
{
fn extend<'a, A, B>(
ts: &'a mut impl Extend<A>,
us: &'a mut impl Extend<B>,
) -> impl FnMut((A, B)) + 'a {
move |(t, u)| {
ts.extend(Some(t));
us.extend(Some(u));
}
}
let mut ts: FromA = Default::default();
let mut us: FromB = Default::default();
self.for_each(extend(&mut ts, &mut us));
(ts, us)
}
/// Creates an iterator which copies 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().copied().collect();
///
/// // copied is the same as .map(|&x| x)
/// 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 = "iter_copied", since = "1.36.0")]
fn copied<'a, T: 'a>(self) -> Copied<Self>
where Self: Sized + Iterator<Item=&'a T>, T: Copy
{
Copied::new(self)
}
/// 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`.
///
/// [`clone`]: ../../std/clone/trait.Clone.html#tymethod.clone
///
/// # 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::new(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.
///
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # 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::new(self)
}
/// Sums the elements of an iterator.
///
/// Takes each element, adds them together, and returns the result.
///
/// An empty iterator returns the zero value of the type.
///
/// # Panics
///
/// When calling `sum()` and a primitive integer type is being returned, this
/// method will panic if the computation overflows and debug assertions are
/// enabled.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let a = [1, 2, 3];
/// let sum: i32 = a.iter().sum();
///
/// assert_eq!(sum, 6);
/// ```
#[stable(feature = "iter_arith", since = "1.11.0")]
fn sum<S>(self) -> S
where Self: Sized,
S: Sum<Self::Item>,
{
Sum::sum(self)
}
/// Iterates over the entire iterator, multiplying all the elements
///
/// An empty iterator returns the one value of the type.
///
/// # Panics
///
/// When calling `product()` and a primitive integer type is being returned,
/// method will panic if the computation overflows and debug assertions are
/// enabled.
///
/// # Examples
///
/// ```
/// fn factorial(n: u32) -> u32 {
/// (1..=n).product()
/// }
/// assert_eq!(factorial(0), 1);
/// assert_eq!(factorial(1), 1);
/// assert_eq!(factorial(5), 120);
/// ```
#[stable(feature = "iter_arith", since = "1.11.0")]
fn product<P>(self) -> P
where Self: Sized,
P: Product<Self::Item>,
{
Product::product(self)
}
/// Lexicographically compares the elements of this `Iterator` with those
/// of another.
///
/// # Examples
///
/// ```
/// use std::cmp::Ordering;
///
/// assert_eq!([1].iter().cmp([1].iter()), Ordering::Equal);
/// assert_eq!([1].iter().cmp([1, 2].iter()), Ordering::Less);
/// assert_eq!([1, 2].iter().cmp([1].iter()), Ordering::Greater);
/// ```
#[stable(feature = "iter_order", since = "1.5.0")]
fn cmp<I>(self, other: I) -> Ordering
where
I: IntoIterator<Item = Self::Item>,
Self::Item: Ord,
Self: Sized,
{
self.cmp_by(other, |x, y| x.cmp(&y))
}
/// Lexicographically compares the elements of this `Iterator` with those
/// of another with respect to the specified comparison function.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(iter_order_by)]
///
/// use std::cmp::Ordering;
///
/// let xs = [1, 2, 3, 4];
/// let ys = [1, 4, 9, 16];
///
/// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| x.cmp(&y)), Ordering::Less);
/// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (x * x).cmp(&y)), Ordering::Equal);
/// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (2 * x).cmp(&y)), Ordering::Greater);
/// ```
#[unstable(feature = "iter_order_by", issue = "0")]
fn cmp_by<I, F>(mut self, other: I, mut cmp: F) -> Ordering
where
Self: Sized,
I: IntoIterator,
F: FnMut(Self::Item, I::Item) -> Ordering,
{
let mut other = other.into_iter();
loop {
let x = match self.next() {
None => if other.next().is_none() {
return Ordering::Equal
} else {
return Ordering::Less
},
Some(val) => val,
};
let y = match other.next() {
None => return Ordering::Greater,
Some(val) => val,
};
match cmp(x, y) {
Ordering::Equal => (),
non_eq => return non_eq,
}
}
}
/// Lexicographically compares the elements of this `Iterator` with those
/// of another.
///
/// # Examples
///
/// ```
/// use std::cmp::Ordering;
///
/// assert_eq!([1.].iter().partial_cmp([1.].iter()), Some(Ordering::Equal));
/// assert_eq!([1.].iter().partial_cmp([1., 2.].iter()), Some(Ordering::Less));
/// assert_eq!([1., 2.].iter().partial_cmp([1.].iter()), Some(Ordering::Greater));
///
/// assert_eq!([std::f64::NAN].iter().partial_cmp([1.].iter()), None);
/// ```
#[stable(feature = "iter_order", since = "1.5.0")]
fn partial_cmp<I>(self, other: I) -> Option<Ordering>
where
I: IntoIterator,
Self::Item: PartialOrd<I::Item>,
Self: Sized,
{
self.partial_cmp_by(other, |x, y| x.partial_cmp(&y))
}
/// Lexicographically compares the elements of this `Iterator` with those
/// of another with respect to the specified comparison function.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(iter_order_by)]
///
/// use std::cmp::Ordering;
///
/// let xs = [1.0, 2.0, 3.0, 4.0];
/// let ys = [1.0, 4.0, 9.0, 16.0];
///
/// assert_eq!(
/// xs.iter().partial_cmp_by(&ys, |&x, &y| x.partial_cmp(&y)),
/// Some(Ordering::Less)
/// );
/// assert_eq!(
/// xs.iter().partial_cmp_by(&ys, |&x, &y| (x * x).partial_cmp(&y)),
/// Some(Ordering::Equal)
/// );
/// assert_eq!(
/// xs.iter().partial_cmp_by(&ys, |&x, &y| (2.0 * x).partial_cmp(&y)),
/// Some(Ordering::Greater)
/// );
/// ```
#[unstable(feature = "iter_order_by", issue = "0")]
fn partial_cmp_by<I, F>(mut self, other: I, mut partial_cmp: F) -> Option<Ordering>
where
Self: Sized,
I: IntoIterator,
F: FnMut(Self::Item, I::Item) -> Option<Ordering>,
{
let mut other = other.into_iter();
loop {
let x = match self.next() {
None => if other.next().is_none() {
return Some(Ordering::Equal)
} else {
return Some(Ordering::Less)
},
Some(val) => val,
};
let y = match other.next() {
None => return Some(Ordering::Greater),
Some(val) => val,
};
match partial_cmp(x, y) {
Some(Ordering::Equal) => (),
non_eq => return non_eq,
}
}
}
/// Determines if the elements of this `Iterator` are equal to those of
/// another.
///
/// # Examples
///
/// ```
/// assert_eq!([1].iter().eq([1].iter()), true);
/// assert_eq!([1].iter().eq([1, 2].iter()), false);
/// ```
#[stable(feature = "iter_order", since = "1.5.0")]
fn eq<I>(self, other: I) -> bool
where
I: IntoIterator,
Self::Item: PartialEq<I::Item>,
Self: Sized,
{
self.eq_by(other, |x, y| x == y)
}
/// Determines if the elements of this `Iterator` are equal to those of
/// another with respect to the specified equality function.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(iter_order_by)]
///
/// let xs = [1, 2, 3, 4];
/// let ys = [1, 4, 9, 16];
///
/// assert!(xs.iter().eq_by(&ys, |&x, &y| x * x == y));
/// ```
#[unstable(feature = "iter_order_by", issue = "0")]
fn eq_by<I, F>(mut self, other: I, mut eq: F) -> bool
where
Self: Sized,
I: IntoIterator,
F: FnMut(Self::Item, I::Item) -> bool,
{
let mut other = other.into_iter();
loop {
let x = match self.next() {
None => return other.next().is_none(),
Some(val) => val,
};
let y = match other.next() {
None => return false,
Some(val) => val,
};
if !eq(x, y) {
return false;
}
}
}
/// Determines if the elements of this `Iterator` are unequal to those of
/// another.
///
/// # Examples
///
/// ```
/// assert_eq!([1].iter().ne([1].iter()), false);
/// assert_eq!([1].iter().ne([1, 2].iter()), true);
/// ```
#[stable(feature = "iter_order", since = "1.5.0")]
fn ne<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialEq<I::Item>,
Self: Sized,
{
!self.eq(other)
}
/// Determines if the elements of this `Iterator` are lexicographically
/// less than those of another.
///
/// # Examples
///
/// ```
/// assert_eq!([1].iter().lt([1].iter()), false);
/// assert_eq!([1].iter().lt([1, 2].iter()), true);
/// assert_eq!([1, 2].iter().lt([1].iter()), false);
/// ```
#[stable(feature = "iter_order", since = "1.5.0")]
fn lt<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<I::Item>,
Self: Sized,
{
self.partial_cmp(other) == Some(Ordering::Less)
}
/// Determines if the elements of this `Iterator` are lexicographically
/// less or equal to those of another.
///
/// # Examples
///
/// ```
/// assert_eq!([1].iter().le([1].iter()), true);
/// assert_eq!([1].iter().le([1, 2].iter()), true);
/// assert_eq!([1, 2].iter().le([1].iter()), false);
/// ```
#[stable(feature = "iter_order", since = "1.5.0")]
fn le<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<I::Item>,
Self: Sized,
{
match self.partial_cmp(other) {
Some(Ordering::Less) | Some(Ordering::Equal) => true,
_ => false,
}
}
/// Determines if the elements of this `Iterator` are lexicographically
/// greater than those of another.
///
/// # Examples
///
/// ```
/// assert_eq!([1].iter().gt([1].iter()), false);
/// assert_eq!([1].iter().gt([1, 2].iter()), false);
/// assert_eq!([1, 2].iter().gt([1].iter()), true);
/// ```
#[stable(feature = "iter_order", since = "1.5.0")]
fn gt<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<I::Item>,
Self: Sized,
{
self.partial_cmp(other) == Some(Ordering::Greater)
}
/// Determines if the elements of this `Iterator` are lexicographically
/// greater than or equal to those of another.
///
/// # Examples
///
/// ```
/// assert_eq!([1].iter().ge([1].iter()), true);
/// assert_eq!([1].iter().ge([1, 2].iter()), false);
/// assert_eq!([1, 2].iter().ge([1].iter()), true);
/// ```
#[stable(feature = "iter_order", since = "1.5.0")]
fn ge<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<I::Item>,
Self: Sized,
{
match self.partial_cmp(other) {
Some(Ordering::Greater) | Some(Ordering::Equal) => true,
_ => false,
}
}
/// Checks if the elements of this iterator are sorted.
///
/// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
/// iterator yields exactly zero or one element, `true` is returned.
///
/// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
/// implies that this function returns `false` if any two consecutive items are not
/// comparable.
///
/// # Examples
///
/// ```
/// #![feature(is_sorted)]
///
/// assert!([1, 2, 2, 9].iter().is_sorted());
/// assert!(![1, 3, 2, 4].iter().is_sorted());
/// assert!([0].iter().is_sorted());
/// assert!(std::iter::empty::<i32>().is_sorted());
/// assert!(![0.0, 1.0, std::f32::NAN].iter().is_sorted());
/// ```
#[inline]
#[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
fn is_sorted(self) -> bool
where
Self: Sized,
Self::Item: PartialOrd,
{
self.is_sorted_by(PartialOrd::partial_cmp)
}
/// Checks if the elements of this iterator are sorted using the given comparator function.
///
/// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
/// function to determine the ordering of two elements. Apart from that, it's equivalent to
/// [`is_sorted`]; see its documentation for more information.
///
/// # Examples
///
/// ```
/// #![feature(is_sorted)]
///
/// assert!([1, 2, 2, 9].iter().is_sorted_by(|a, b| a.partial_cmp(b)));
/// assert!(![1, 3, 2, 4].iter().is_sorted_by(|a, b| a.partial_cmp(b)));
/// assert!([0].iter().is_sorted_by(|a, b| a.partial_cmp(b)));
/// assert!(std::iter::empty::<i32>().is_sorted_by(|a, b| a.partial_cmp(b)));
/// assert!(![0.0, 1.0, std::f32::NAN].iter().is_sorted_by(|a, b| a.partial_cmp(b)));
/// ```
///
/// [`is_sorted`]: trait.Iterator.html#method.is_sorted
#[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
fn is_sorted_by<F>(mut self, mut compare: F) -> bool
where
Self: Sized,
F: FnMut(&Self::Item, &Self::Item) -> Option<Ordering>
{
let mut last = match self.next() {
Some(e) => e,
None => return true,
};
while let Some(curr) = self.next() {
if let Some(Ordering::Greater) | None = compare(&last, &curr) {
return false;
}
last = curr;
}
true
}
/// Checks if the elements of this iterator are sorted using the given key extraction
/// function.
///
/// Instead of comparing the iterator's elements directly, this function compares the keys of
/// the elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see
/// its documentation for more information.
///
/// [`is_sorted`]: trait.Iterator.html#method.is_sorted
///
/// # Examples
///
/// ```
/// #![feature(is_sorted)]
///
/// assert!(["c", "bb", "aaa"].iter().is_sorted_by_key(|s| s.len()));
/// assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs()));
/// ```
#[inline]
#[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
fn is_sorted_by_key<F, K>(self, f: F) -> bool
where
Self: Sized,
F: FnMut(Self::Item) -> K,
K: PartialOrd
{
self.map(f).is_sorted()
}
}
/// Select an element from an iterator based on the given "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, F>(mut it: I, f: F) -> Option<I::Item>
where
I: Iterator,
F: FnMut(&I::Item, &I::Item) -> bool,
{
#[inline]
fn select<T>(mut f: impl FnMut(&T, &T) -> bool) -> impl FnMut(T, T) -> T {
move |sel, x| if f(&sel, &x) { x } else { sel }
}
// 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).
let first = it.next()?;
Some(it.fold(first, select(f)))
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator + ?Sized> Iterator for &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() }
fn nth(&mut self, n: usize) -> Option<Self::Item> {
(**self).nth(n)
}
}