pub trait Iterator {
type Item;
Show 76 methods // Required method
fn next(&mut self) -> Option<Self::Item>;
// Provided methods
fn next_chunk<const N: usize>(
&mut self,
) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>
where Self: Sized { ... }
fn size_hint(&self) -> (usize, Option<usize>) { ... }
fn count(self) -> usize
where Self: Sized { ... }
fn last(self) -> Option<Self::Item>
where Self: Sized { ... }
fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> { ... }
fn nth(&mut self, n: usize) -> Option<Self::Item> { ... }
fn step_by(self, step: usize) -> StepBy<Self> â
where Self: Sized { ... }
fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter> â
where Self: Sized,
U: IntoIterator<Item = Self::Item> { ... }
fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter> â
where Self: Sized,
U: IntoIterator { ... }
fn intersperse(self, separator: Self::Item) -> Intersperse<Self> â
where Self: Sized,
Self::Item: Clone { ... }
fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G> â
where Self: Sized,
G: FnMut() -> Self::Item { ... }
fn map<B, F>(self, f: F) -> Map<Self, F> â
where Self: Sized,
F: FnMut(Self::Item) -> B { ... }
fn for_each<F>(self, f: F)
where Self: Sized,
F: FnMut(Self::Item) { ... }
fn filter<P>(self, predicate: P) -> Filter<Self, P> â
where Self: Sized,
P: FnMut(&Self::Item) -> bool { ... }
fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> â
where Self: Sized,
F: FnMut(Self::Item) -> Option<B> { ... }
fn enumerate(self) -> Enumerate<Self> â
where Self: Sized { ... }
fn peekable(self) -> Peekable<Self> â
where Self: Sized { ... }
fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> â
where Self: Sized,
P: FnMut(&Self::Item) -> bool { ... }
fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> â
where Self: Sized,
P: FnMut(&Self::Item) -> bool { ... }
fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> â
where Self: Sized,
P: FnMut(Self::Item) -> Option<B> { ... }
fn skip(self, n: usize) -> Skip<Self> â
where Self: Sized { ... }
fn take(self, n: usize) -> Take<Self> â
where Self: Sized { ... }
fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> â
where Self: Sized,
F: FnMut(&mut St, Self::Item) -> Option<B> { ... }
fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> â
where Self: Sized,
U: IntoIterator,
F: FnMut(Self::Item) -> U { ... }
fn flatten(self) -> Flatten<Self> â
where Self: Sized,
Self::Item: IntoIterator { ... }
fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N> â
where Self: Sized,
F: FnMut(&[Self::Item; N]) -> R { ... }
fn fuse(self) -> Fuse<Self> â
where Self: Sized { ... }
fn inspect<F>(self, f: F) -> Inspect<Self, F> â
where Self: Sized,
F: FnMut(&Self::Item) { ... }
fn by_ref(&mut self) -> &mut Self
where Self: Sized { ... }
fn collect<B>(self) -> B
where B: FromIterator<Self::Item>,
Self: Sized { ... }
fn try_collect<B>(
&mut self,
) -> <<Self::Item as Try>::Residual as Residual<B>>::TryType
where Self: Sized,
Self::Item: Try,
<Self::Item as Try>::Residual: Residual<B>,
B: FromIterator<<Self::Item as Try>::Output> { ... }
fn collect_into<E>(self, collection: &mut E) -> &mut E
where E: Extend<Self::Item>,
Self: Sized { ... }
fn partition<B, F>(self, f: F) -> (B, B)
where Self: Sized,
B: Default + Extend<Self::Item>,
F: FnMut(&Self::Item) -> bool { ... }
fn partition_in_place<'a, T, P>(self, predicate: P) -> usize
where T: 'a,
Self: Sized + DoubleEndedIterator<Item = &'a mut T>,
P: FnMut(&T) -> bool { ... }
fn is_partitioned<P>(self, predicate: P) -> bool
where Self: Sized,
P: FnMut(Self::Item) -> bool { ... }
fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
where Self: Sized,
F: FnMut(B, Self::Item) -> R,
R: Try<Output = B> { ... }
fn try_for_each<F, R>(&mut self, f: F) -> R
where Self: Sized,
F: FnMut(Self::Item) -> R,
R: Try<Output = ()> { ... }
fn fold<B, F>(self, init: B, f: F) -> B
where Self: Sized,
F: FnMut(B, Self::Item) -> B { ... }
fn reduce<F>(self, f: F) -> Option<Self::Item>
where Self: Sized,
F: FnMut(Self::Item, Self::Item) -> Self::Item { ... }
fn try_reduce<R>(
&mut self,
f: impl FnMut(Self::Item, Self::Item) -> R,
) -> <<R as Try>::Residual as Residual<Option<<R as Try>::Output>>>::TryType
where Self: Sized,
R: Try<Output = Self::Item>,
<R as Try>::Residual: Residual<Option<Self::Item>> { ... }
fn all<F>(&mut self, f: F) -> bool
where Self: Sized,
F: FnMut(Self::Item) -> bool { ... }
fn any<F>(&mut self, f: F) -> bool
where Self: Sized,
F: FnMut(Self::Item) -> bool { ... }
fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
where Self: Sized,
P: FnMut(&Self::Item) -> bool { ... }
fn find_map<B, F>(&mut self, f: F) -> Option<B>
where Self: Sized,
F: FnMut(Self::Item) -> Option<B> { ... }
fn try_find<R>(
&mut self,
f: impl FnMut(&Self::Item) -> R,
) -> <<R as Try>::Residual as Residual<Option<Self::Item>>>::TryType
where Self: Sized,
R: Try<Output = bool>,
<R as Try>::Residual: Residual<Option<Self::Item>> { ... }
fn position<P>(&mut self, predicate: P) -> Option<usize>
where Self: Sized,
P: FnMut(Self::Item) -> bool { ... }
fn rposition<P>(&mut self, predicate: P) -> Option<usize>
where P: FnMut(Self::Item) -> bool,
Self: Sized + ExactSizeIterator + DoubleEndedIterator { ... }
fn max(self) -> Option<Self::Item>
where Self: Sized,
Self::Item: Ord { ... }
fn min(self) -> Option<Self::Item>
where Self: Sized,
Self::Item: Ord { ... }
fn max_by_key<B, F>(self, f: F) -> Option<Self::Item>
where B: Ord,
Self: Sized,
F: FnMut(&Self::Item) -> B { ... }
fn max_by<F>(self, compare: F) -> Option<Self::Item>
where Self: Sized,
F: FnMut(&Self::Item, &Self::Item) -> Ordering { ... }
fn min_by_key<B, F>(self, f: F) -> Option<Self::Item>
where B: Ord,
Self: Sized,
F: FnMut(&Self::Item) -> B { ... }
fn min_by<F>(self, compare: F) -> Option<Self::Item>
where Self: Sized,
F: FnMut(&Self::Item, &Self::Item) -> Ordering { ... }
fn rev(self) -> Rev<Self> â
where Self: Sized + DoubleEndedIterator { ... }
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 copied<'a, T>(self) -> Copied<Self> â
where T: 'a + Copy,
Self: Sized + Iterator<Item = &'a T> { ... }
fn cloned<'a, T>(self) -> Cloned<Self> â
where T: 'a + Clone,
Self: Sized + Iterator<Item = &'a T> { ... }
fn cycle(self) -> Cycle<Self> â
where Self: Sized + Clone { ... }
fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N> â
where Self: Sized { ... }
fn sum<S>(self) -> S
where Self: Sized,
S: Sum<Self::Item> { ... }
fn product<P>(self) -> P
where Self: Sized,
P: Product<Self::Item> { ... }
fn cmp<I>(self, other: I) -> Ordering
where I: IntoIterator<Item = Self::Item>,
Self::Item: Ord,
Self: Sized { ... }
fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering
where Self: Sized,
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Ordering { ... }
fn partial_cmp<I>(self, other: I) -> Option<Ordering>
where I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
Self: Sized { ... }
fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>
where Self: Sized,
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Option<Ordering> { ... }
fn eq<I>(self, other: I) -> bool
where I: IntoIterator,
Self::Item: PartialEq<<I as IntoIterator>::Item>,
Self: Sized { ... }
fn eq_by<I, F>(self, other: I, eq: F) -> bool
where Self: Sized,
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> bool { ... }
fn ne<I>(self, other: I) -> bool
where I: IntoIterator,
Self::Item: PartialEq<<I as IntoIterator>::Item>,
Self: Sized { ... }
fn lt<I>(self, other: I) -> bool
where I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
Self: Sized { ... }
fn le<I>(self, other: I) -> bool
where I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
Self: Sized { ... }
fn gt<I>(self, other: I) -> bool
where I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
Self: Sized { ... }
fn ge<I>(self, other: I) -> bool
where I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
Self: Sized { ... }
fn is_sorted(self) -> bool
where Self: Sized,
Self::Item: PartialOrd { ... }
fn is_sorted_by<F>(self, compare: F) -> bool
where Self: Sized,
F: FnMut(&Self::Item, &Self::Item) -> bool { ... }
fn is_sorted_by_key<F, K>(self, f: F) -> bool
where Self: Sized,
F: FnMut(Self::Item) -> K,
K: PartialOrd { ... }
}A trait 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.
The type of the elements being iterated over.
1.0.0 · SourceAdvances 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.
let a = [1, 2, 3];
let mut iter = a.iter();
assert_eq!(Some(&1), iter.next());
assert_eq!(Some(&2), iter.next());
assert_eq!(Some(&3), iter.next());
assert_eq!(None, iter.next());
assert_eq!(None, iter.next());
assert_eq!(None, iter.next());iter_next_chunk #98326)
Advances the iterator and returns an array containing the next N values.
If there are not enough elements to fill the array then Err is returned containing an iterator over the remaining elements.
Basic usage:
#![feature(iter_next_chunk)]
let mut iter = "lorem".chars();
assert_eq!(iter.next_chunk().unwrap(), ['l', 'o']); assert_eq!(iter.next_chunk().unwrap(), ['r', 'e', 'm']); assert_eq!(iter.next_chunk::<4>().unwrap_err().as_slice(), &[]); Split a string and get the first three items.
#![feature(iter_next_chunk)]
let quote = "not all those who wander are lost";
let [first, second, third] = quote.split_whitespace().next_chunk().unwrap();
assert_eq!(first, "not");
assert_eq!(second, "all");
assert_eq!(third, "those");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.
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 traitâs protocol.
The default implementation returns (0, None) which is correct for any iterator.
Basic usage:
let a = [1, 2, 3];
let mut iter = a.iter();
assert_eq!((3, Some(3)), iter.size_hint());
let _ = iter.next();
assert_eq!((2, Some(2)), iter.size_hint());A more complex example:
let iter = (0..10).filter(|x| x % 2 == 0);
assert_eq!((0, Some(10)), iter.size_hint());
let iter = (0..10).filter(|x| x % 2 == 0).chain(15..20);
assert_eq!((5, Some(15)), iter.size_hint());Returning None for an upper bound:
let iter = 0..;
assert_eq!((usize::MAX, None), iter.size_hint());Consumes the iterator, counting the number of iterations and returning it.
This method will call next repeatedly until None is encountered, returning the number of times it saw Some. Note that next has to be called at least once even if the iterator does not have any elements.
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.
This function might panic if the iterator has more than usize::MAX elements.
let a = [1, 2, 3];
assert_eq!(a.iter().count(), 3);
let a = [1, 2, 3, 4, 5];
assert_eq!(a.iter().count(), 5);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.
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));iter_advance_by #77404)
Advances the iterator by n elements.
This method will eagerly skip n elements by calling next up to n times until None is encountered.
advance_by(n) will return Ok(()) if the iterator successfully advances by n elements, or a Err(NonZero<usize>) with value k if None is encountered, where k is remaining number of steps that could not be advanced because the iterator ran out. If self is empty and n is non-zero, then this returns Err(n). Otherwise, k is always less than n.
Calling advance_by(0) can do meaningful work, for example Flatten can advance its outer iterator until it finds an inner iterator that is not empty, which then often allows it to return a more accurate size_hint() than in its initial state.
#![feature(iter_advance_by)]
use std::num::NonZero;
let a = [1, 2, 3, 4];
let mut iter = a.iter();
assert_eq!(iter.advance_by(2), Ok(()));
assert_eq!(iter.next(), Some(&3));
assert_eq!(iter.advance_by(0), Ok(()));
assert_eq!(iter.advance_by(100), Err(NonZero::new(99).unwrap())); Returns the nth 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.
Basic usage:
let a = [1, 2, 3];
assert_eq!(a.iter().nth(1), Some(&2));Calling nth() multiple times doesnât 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);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 self.next(), self.nth(step-1), self.nth(step-1), â¦, but is also free to behave like the sequence advance_n_and_return_first(&mut self, step), advance_n_and_return_first(&mut self, 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, n: usize) -> Option<I::Item>
where
I: Iterator,
{
let next = iter.next();
if n > 1 {
iter.nth(n - 2);
}
next
}The method will panic if the given step is 0.
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);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. ð
once is commonly used to adapt a single value into a chain of other kinds of iteration.
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:
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);If you work with Windows API, you may wish to convert OsStr to Vec<u16>:
#[cfg(windows)]
fn os_str_to_utf16(s: &std::ffi::OsStr) -> Vec<u16> {
use std::os::windows::ffi::OsStrExt;
s.encode_wide().chain(std::iter::once(0)).collect()
}âZips upâ 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 zipped iterator has no more elements to return then each further attempt to advance it will first try to advance the first iterator at most one time and if it still yielded an item try to advance the second iterator at most one time.
To âundoâ the result of zipping up two iterators, see unzip.
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:
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]);If both iterators have roughly equivalent syntax, it may be more readable to use zip:
use std::iter::zip;
let a = [1, 2, 3];
let b = [2, 3, 4];
let mut zipped = zip(
a.into_iter().map(|x| x * 2).skip(1),
b.into_iter().map(|x| x * 2).skip(1),
);
assert_eq!(zipped.next(), Some((4, 6)));
assert_eq!(zipped.next(), Some((6, 8)));
assert_eq!(zipped.next(), None);compared to:
let mut zipped = a
.into_iter()
.map(|x| x * 2)
.skip(1)
.zip(b.into_iter().map(|x| x * 2).skip(1));iter_intersperse #79524)
Creates a new iterator which places a copy of separator between adjacent items of the original iterator.
In case separator does not implement Clone or needs to be computed every time, use intersperse_with.
Basic usage:
#![feature(iter_intersperse)]
let mut a = [0, 1, 2].iter().intersperse(&100);
assert_eq!(a.next(), Some(&0)); assert_eq!(a.next(), Some(&100)); assert_eq!(a.next(), Some(&1)); assert_eq!(a.next(), Some(&100)); assert_eq!(a.next(), Some(&2)); assert_eq!(a.next(), None); intersperse can be very useful to join an iteratorâs items using a common element:
#![feature(iter_intersperse)]
let hello = ["Hello", "World", "!"].iter().copied().intersperse(" ").collect::<String>();
assert_eq!(hello, "Hello World !");iter_intersperse #79524)
Creates a new iterator which places an item generated by separator between adjacent items of the original iterator.
The closure will be called exactly once each time an item is placed between two adjacent items from the underlying iterator; specifically, the closure is not called if the underlying iterator yields less than two items and after the last item is yielded.
If the iteratorâs item implements Clone, it may be easier to use intersperse.
Basic usage:
#![feature(iter_intersperse)]
#[derive(PartialEq, Debug)]
struct NotClone(usize);
let v = [NotClone(0), NotClone(1), NotClone(2)];
let mut it = v.into_iter().intersperse_with(|| NotClone(99));
assert_eq!(it.next(), Some(NotClone(0))); assert_eq!(it.next(), Some(NotClone(99))); assert_eq!(it.next(), Some(NotClone(1))); assert_eq!(it.next(), Some(NotClone(99))); assert_eq!(it.next(), Some(NotClone(2))); assert_eq!(it.next(), None); intersperse_with can be used in situations where the separator needs to be computed:
#![feature(iter_intersperse)]
let src = ["Hello", "to", "all", "people", "!!"].iter().copied();
let mut happy_emojis = [" â¤ï¸ ", " ð "].iter().copied();
let separator = || happy_emojis.next().unwrap_or(" ð¦ ");
let result = src.intersperse_with(separator).collect::<String>();
assert_eq!(result, "Hello â¤ï¸ to ð all ð¦ people ð¦ !!");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 youâre already working with other iterators. If youâre doing some sort of looping for a side effect, itâs considered more idiomatic to use for than map().
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 youâre doing some sort of side effect, prefer for to map():
(0..5).map(|x| println!("{x}"));
for x in 0..5 {
println!("{x}");
}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. Itâs 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 adapters like Chain.
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}"));Creates an iterator which uses a closure to determine if an element should be yielded.
Given an element the closure must return true or false. The returned iterator will yield only the elements for which the closure returns true.
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); assert_eq!(iter.next(), Some(&2));
assert_eq!(iter.next(), None);Itâs 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); 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); assert_eq!(iter.next(), Some(&2));
assert_eq!(iter.next(), None);of these layers.
Note that iter.filter(f).next() is equivalent to iter.find(f).
Creates an iterator that both filters and maps.
The returned iterator yields only the values for which the supplied closure returns Some(value).
filter_map can be used to make chains of filter and map more concise. The example below shows how a map().filter().map() can be shortened to a single call to filter_map.
Basic usage:
let a = ["1", "two", "NaN", "four", "5"];
let mut iter = a.iter().filter_map(|s| s.parse().ok());
assert_eq!(iter.next(), Some(1));
assert_eq!(iter.next(), Some(5));
assert_eq!(iter.next(), None);Hereâs the same example, but with filter and map:
let a = ["1", "two", "NaN", "four", "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(5));
assert_eq!(iter.next(), None);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.
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.
The returned iterator might panic if the to-be-returned index would overflow a usize.
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);Creates an iterator which can use the peek and peek_mut methods to look at the next element of the iterator without consuming it. See their documentation for more information.
Note that the underlying iterator is still advanced when peek or peek_mut are 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.
Basic usage:
let xs = [1, 2, 3];
let mut iter = xs.iter().peekable();
assert_eq!(iter.peek(), Some(&&1));
assert_eq!(iter.next(), Some(&1));
assert_eq!(iter.next(), Some(&2));
assert_eq!(iter.peek(), Some(&&3));
assert_eq!(iter.peek(), Some(&&3));
assert_eq!(iter.next(), Some(&3));
assert_eq!(iter.peek(), None);
assert_eq!(iter.next(), None);Using peek_mut to mutate the next item without advancing the iterator:
let xs = [1, 2, 3];
let mut iter = xs.iter().peekable();
assert_eq!(iter.peek_mut(), Some(&mut &1));
assert_eq!(iter.peek_mut(), Some(&mut &1));
assert_eq!(iter.next(), Some(&1));
if let Some(mut p) = iter.peek_mut() {
assert_eq!(*p, &2);
*p = &1000;
}
assert_eq!(iter.collect::<Vec<_>>(), vec![&1000, &3]);Creates an iterator that skips elements based on a predicate.
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()âs job is over, and the rest of the elements are yielded.
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 argument is a double reference:
let a = [-1, 0, 1];
let mut iter = a.iter().skip_while(|x| **x < 0); 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));
assert_eq!(iter.next(), Some(&-2));
assert_eq!(iter.next(), None);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()âs job is over, and the rest of the elements are ignored.
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); 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));
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 wasnât placed back into the iterator.
Creates an iterator that both yields elements based on a predicate and maps.
map_while() takes a closure as an argument. It will call this closure on each element of the iterator, and yield elements while it returns Some(_).
Basic usage:
let a = [-1i32, 4, 0, 1];
let mut iter = a.iter().map_while(|x| 16i32.checked_div(*x));
assert_eq!(iter.next(), Some(-16));
assert_eq!(iter.next(), Some(4));
assert_eq!(iter.next(), None);Hereâs the same example, but with take_while and map:
let a = [-1i32, 4, 0, 1];
let mut iter = a.iter()
.map(|x| 16i32.checked_div(*x))
.take_while(|x| x.is_some())
.map(|x| x.unwrap());
assert_eq!(iter.next(), Some(-16));
assert_eq!(iter.next(), Some(4));
assert_eq!(iter.next(), None);Stopping after an initial None:
let a = [0, 1, 2, -3, 4, 5, -6];
let iter = a.iter().map_while(|x| u32::try_from(*x).ok());
let vec = iter.collect::<Vec<_>>();
assert_eq!(vec, vec![0, 1, 2]);Because map_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<u32> = iter.by_ref()
.map_while(|n| u32::try_from(*n).ok())
.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 wasnât placed back into the iterator.
Note that unlike take_while this iterator is not fused. It is also not specified what this iterator returns after the first None is returned. If you need fused iterator, use fuse.
Creates an iterator that skips the first n elements.
skip(n) skips elements until n elements are skipped or the end of the iterator is reached (whichever happens first). After that, all the remaining elements are yielded. In particular, if the original iterator is too short, then the returned iterator is empty.
Rather than overriding this method directly, instead override the nth method.
let a = [1, 2, 3];
let mut iter = a.iter().skip(2);
assert_eq!(iter.next(), Some(&3));
assert_eq!(iter.next(), None);Creates an iterator that yields the first n elements, or fewer if the underlying iterator ends sooner.
take(n) yields elements until n elements are yielded or the end of the iterator is reached (whichever happens first). The returned iterator is a prefix of length n if the original iterator contains at least n elements, otherwise it contains all of the (fewer than n) elements of the original iterator.
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);If less than n elements are available, take will limit itself to the size of the underlying iterator:
let v = [1, 2];
let mut iter = v.into_iter().take(5);
assert_eq!(iter.next(), Some(1));
assert_eq!(iter.next(), Some(2));
assert_eq!(iter.next(), None);An iterator adapter which, like fold, holds internal state, but unlike fold, produces a new iterator.
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 returned by the next method. Thus the closure can return Some(value) to yield value, or None to end the iteration.
let a = [1, 2, 3, 4];
let mut iter = a.iter().scan(1, |state, &x| {
*state = *state * x;
if *state > 6 {
return None;
}
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);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, thereâs 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 mapping, and then flattening as in map(f).flatten().
Another way of thinking about flat_map(): mapâs closure returns one item for each element, and flat_map()âs closure returns an iterator for each element.
let words = ["alpha", "beta", "gamma"];
let merged: String = words.iter()
.flat_map(|s| s.chars())
.collect();
assert_eq!(merged, "alphabetagamma");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.
§ExamplesBasic 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"];
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"];
let merged: String = words.iter()
.flat_map(|s| s.chars())
.collect();
assert_eq!(merged, "alphabetagamma");Flattening works on any IntoIterator type, including Option and Result:
let options = vec![Some(123), Some(321), None, Some(231)];
let flattened_options: Vec<_> = options.into_iter().flatten().collect();
assert_eq!(flattened_options, vec![123, 321, 231]);
let results = vec![Ok(123), Ok(321), Err(456), Ok(231)];
let flattened_results: Vec<_> = results.into_iter().flatten().collect();
assert_eq!(flattened_results, vec![123, 321, 231]);Flattening only removes one level of nesting at a time:
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 âdeepâ 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.
iter_map_windows #87155)
Calls the given function f for each contiguous window of size N over self and returns an iterator over the outputs of f. Like slice::windows(), the windows during mapping overlap as well.
In the following example, the closure is called three times with the arguments &['a', 'b'], &['b', 'c'] and &['c', 'd'] respectively.
#![feature(iter_map_windows)]
let strings = "abcd".chars()
.map_windows(|[x, y]| format!("{}+{}", x, y))
.collect::<Vec<String>>();
assert_eq!(strings, vec!["a+b", "b+c", "c+d"]);Note that the const parameter N is usually inferred by the destructured argument in the closure.
The returned iterator yields ð â N + 1 items (where ð is the number of items yielded by self). If ð is less than N, this method yields an empty iterator.
The returned iterator implements FusedIterator, because once self returns None, even if it returns a Some(T) again in the next iterations, we cannot put it into a contiguous array buffer, and thus the returned iterator should be fused.
Panics if N is zero. This check will most probably get changed to a compile time error before this method gets stabilized.
#![feature(iter_map_windows)]
let iter = std::iter::repeat(0).map_windows(|&[]| ());Building the sums of neighboring numbers.
#![feature(iter_map_windows)]
let mut it = [1, 3, 8, 1].iter().map_windows(|&[a, b]| a + b);
assert_eq!(it.next(), Some(4)); assert_eq!(it.next(), Some(11)); assert_eq!(it.next(), Some(9)); assert_eq!(it.next(), None);Since the elements in the following example implement Copy, we can just copy the array and get an iterator over the windows.
#![feature(iter_map_windows)]
let mut it = "ferris".chars().map_windows(|w: &[_; 3]| *w);
assert_eq!(it.next(), Some(['f', 'e', 'r']));
assert_eq!(it.next(), Some(['e', 'r', 'r']));
assert_eq!(it.next(), Some(['r', 'r', 'i']));
assert_eq!(it.next(), Some(['r', 'i', 's']));
assert_eq!(it.next(), None);You can also use this function to check the sortedness of an iterator. For the simple case, rather use Iterator::is_sorted.
#![feature(iter_map_windows)]
let mut it = [0.5, 1.0, 3.5, 3.0, 8.5, 8.5, f32::NAN].iter()
.map_windows(|[a, b]| a <= b);
assert_eq!(it.next(), Some(true)); assert_eq!(it.next(), Some(true)); assert_eq!(it.next(), Some(false)); assert_eq!(it.next(), Some(true)); assert_eq!(it.next(), Some(true)); assert_eq!(it.next(), Some(false)); assert_eq!(it.next(), None);For non-fused iterators, they are fused after map_windows.
#![feature(iter_map_windows)]
#[derive(Default)]
struct NonFusedIterator {
state: i32,
}
impl Iterator for NonFusedIterator {
type Item = i32;
fn next(&mut self) -> Option<i32> {
let val = self.state;
self.state = self.state + 1;
if val < 5 || val % 2 == 0 {
Some(val)
} else {
None
}
}
}
let mut iter = NonFusedIterator::default();
assert_eq!(iter.next(), Some(0));
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(), None);
assert_eq!(iter.next(), Some(6));
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), Some(8));
assert_eq!(iter.next(), None);
let mut iter = NonFusedIterator::default()
.map_windows(|arr: &[_; 2]| *arr);
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(), Some([3, 4]));
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), 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.
Note that the Fuse wrapper is a no-op on iterators that implement the FusedIterator trait. fuse() may therefore behave incorrectly if the FusedIterator trait is improperly implemented.
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 val % 2 == 0 {
Some(val)
} else {
None
}
}
}
let mut iter = Alternate { state: 0 };
assert_eq!(iter.next(), Some(0));
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), Some(2));
assert_eq!(iter.next(), None);
let mut iter = iter.fuse();
assert_eq!(iter.next(), Some(4));
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), None);Does something with each element of an iterator, passing the value on.
When using iterators, youâll often chain several of them together. While working on such code, you might want to check out whatâs happening at various parts in the pipeline. To do that, insert a call to inspect().
Itâs 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.
Basic usage:
let a = [1, 4, 2, 3];
let sum = a.iter()
.cloned()
.filter(|x| x % 2 == 0)
.fold(0, |sum, i| sum + i);
println!("{sum}");
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:
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
6Logging 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:
Parsing error: invalid digit found in string
Sum: 3Borrows an iterator, rather than consuming it.
This is useful to allow applying iterator adapters while still retaining ownership of the original iterator.
§Exampleslet mut words = ["hello", "world", "of", "Rust"].into_iter();
let hello_world: Vec<_> = words.by_ref().take(2).collect();
assert_eq!(hello_world, vec!["hello", "world"]);
let of_rust: Vec<_> = words.collect();
assert_eq!(of_rust, vec!["of", "Rust"]);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.
collect() can also create instances of types that are not typical collections. For example, a String can be built from chars, and an iterator of Result<T, E> items can be collected into 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 youâll see the syntax affectionately known as the âturbofishâ: ::<>. This helps the inference algorithm understand specifically which collection youâre trying to collect into.
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:
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 âturbofishâ 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 youâre 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();
assert_eq!(Err("nope"), result);
let results = [Ok(1), Ok(3)];
let result: Result<Vec<_>, &str> = results.iter().cloned().collect();
assert_eq!(Ok(vec![1, 3]), result);iterator_try_collect #94047)
Fallibly transforms an iterator into a collection, short circuiting if a failure is encountered.
try_collect() is a variation of collect() that allows fallible conversions during collection. Its main use case is simplifying conversions from iterators yielding Option<T> into Option<Collection<T>>, or similarly for other Try types (e.g. Result).
Importantly, try_collect() doesnât require that the outer Try type also implements FromIterator; only the inner type produced on Try::Output must implement it. Concretely, this means that collecting into ControlFlow<_, Vec<i32>> is valid because Vec<i32> implements FromIterator, even though ControlFlow doesnât.
Also, if a failure is encountered during try_collect(), the iterator is still valid and may continue to be used, in which case it will continue iterating starting after the element that triggered the failure. See the last example below for an example of how this works.
Successfully collecting an iterator of Option<i32> into Option<Vec<i32>>:
#![feature(iterator_try_collect)]
let u = vec![Some(1), Some(2), Some(3)];
let v = u.into_iter().try_collect::<Vec<i32>>();
assert_eq!(v, Some(vec![1, 2, 3]));Failing to collect in the same way:
#![feature(iterator_try_collect)]
let u = vec![Some(1), Some(2), None, Some(3)];
let v = u.into_iter().try_collect::<Vec<i32>>();
assert_eq!(v, None);A similar example, but with Result:
#![feature(iterator_try_collect)]
let u: Vec<Result<i32, ()>> = vec![Ok(1), Ok(2), Ok(3)];
let v = u.into_iter().try_collect::<Vec<i32>>();
assert_eq!(v, Ok(vec![1, 2, 3]));
let u = vec![Ok(1), Ok(2), Err(()), Ok(3)];
let v = u.into_iter().try_collect::<Vec<i32>>();
assert_eq!(v, Err(()));Finally, even ControlFlow works, despite the fact that it doesnât implement FromIterator. Note also that the iterator can continue to be used, even if a failure is encountered:
#![feature(iterator_try_collect)]
use core::ops::ControlFlow::{Break, Continue};
let u = [Continue(1), Continue(2), Break(3), Continue(4), Continue(5)];
let mut it = u.into_iter();
let v = it.try_collect::<Vec<_>>();
assert_eq!(v, Break(3));
let v = it.try_collect::<Vec<_>>();
assert_eq!(v, Continue(vec![4, 5]));iter_collect_into #94780)
Collects all the items from an iterator into a collection.
This method consumes the iterator and adds all its items to the passed collection. The collection is then returned, so the call chain can be continued.
This is useful when you already have a collection and want to add the iterator items to it.
This method is a convenience method to call Extend::extend, but instead of being called on a collection, itâs called on an iterator.
§ExamplesBasic usage:
#![feature(iter_collect_into)]
let a = [1, 2, 3];
let mut vec: Vec::<i32> = vec![0, 1];
a.iter().map(|&x| x * 2).collect_into(&mut vec);
a.iter().map(|&x| x * 10).collect_into(&mut vec);
assert_eq!(vec, vec![0, 1, 2, 4, 6, 10, 20, 30]);Vec can have a manual set capacity to avoid reallocating it:
#![feature(iter_collect_into)]
let a = [1, 2, 3];
let mut vec: Vec::<i32> = Vec::with_capacity(6);
a.iter().map(|&x| x * 2).collect_into(&mut vec);
a.iter().map(|&x| x * 10).collect_into(&mut vec);
assert_eq!(6, vec.capacity());
assert_eq!(vec, vec![2, 4, 6, 10, 20, 30]);The returned mutable reference can be used to continue the call chain:
#![feature(iter_collect_into)]
let a = [1, 2, 3];
let mut vec: Vec::<i32> = Vec::with_capacity(6);
let count = a.iter().collect_into(&mut vec).iter().count();
assert_eq!(count, vec.len());
assert_eq!(vec, vec![1, 2, 3]);
let count = a.iter().collect_into(&mut vec).iter().count();
assert_eq!(count, vec.len());
assert_eq!(vec, vec![1, 2, 3, 1, 2, 3]);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().
let a = [1, 2, 3];
let (even, odd): (Vec<_>, Vec<_>) = a
.into_iter()
.partition(|n| n % 2 == 0);
assert_eq!(even, vec![2]);
assert_eq!(odd, vec![1, 3]);iter_partition_in_place #62543)
Reorders 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.
§Current implementationThe current algorithm tries to find the first element for which the predicate evaluates to false and the last element for which it evaluates to true, and repeatedly swaps them.
Time complexity: O(n)
See also is_partitioned() and partition().
#![feature(iter_partition_in_place)]
let mut a = [1, 2, 3, 4, 5, 6, 7];
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)); assert!(a[i..].iter().all(|&n| n % 2 == 1)); iter_is_partitioned #62544)
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().
#![feature(iter_is_partitioned)]
assert!("Iterator".chars().is_partitioned(char::is_uppercase));
assert!(!"IntoIterator".chars().is_partitioned(char::is_uppercase));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 âaccumulatorâ, 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 ImplementorsSeveral 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.
Basic usage:
let a = [1, 2, 3];
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();
let sum = it.try_fold(0i8, |acc, &x| acc.checked_add(x));
assert_eq!(sum, None);
assert_eq!(it.len(), 2);
assert_eq!(it.next(), Some(&40));While you cannot break from a closure, the ControlFlow type allows a similar idea:
use std::ops::ControlFlow;
let triangular = (1..30).try_fold(0_i8, |prev, x| {
if let Some(next) = prev.checked_add(x) {
ControlFlow::Continue(next)
} else {
ControlFlow::Break(prev)
}
});
assert_eq!(triangular, ControlFlow::Break(120));
let triangular = (1..30).try_fold(0_u64, |prev, x| {
if let Some(next) = prev.checked_add(x) {
ControlFlow::Continue(next)
} else {
ControlFlow::Break(prev)
}
});
assert_eq!(triangular, ControlFlow::Continue(435));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().
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());
assert_eq!(it.next(), Some("stale_bread.json"));The ControlFlow type can be used with this method for the situations in which youâd use break and continue in a normal loop:
use std::ops::ControlFlow;
let r = (2..100).try_for_each(|x| {
if 323 % x == 0 {
return ControlFlow::Break(x)
}
ControlFlow::Continue(())
});
assert_eq!(r, ControlFlow::Break(17));Folds every element into an accumulator by applying an operation, returning the final result.
fold() takes two arguments: an initial value, and a closure with two arguments: an âaccumulatorâ, 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 âreduceâ or âinjectâ.
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, might not terminate for infinite iterators, even on traits for which a result is determinable in finite time.
Note: reduce() can be used to use the first element as the initial value, if the accumulator type and item type is the same.
Note: fold() combines elements in a left-associative fashion. For associative operators like +, the order the elements are combined in is not important, but for non-associative operators like - the order will affect the final result. For a right-associative version of fold(), see DoubleEndedIterator::rfold().
Several 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 fold() on the internal parts from which this iterator is composed.
Basic usage:
let a = [1, 2, 3];
let sum = a.iter().fold(0, |acc, x| acc + x);
assert_eq!(sum, 6);Letâs walk through each step of the iteration here:
element acc x result 0 1 0 1 1 2 1 2 3 3 3 3 6And so, our final result, 6.
This example demonstrates the left-associative nature of fold(): it builds a string, starting with an initial value and continuing with each element from the front until the back:
let numbers = [1, 2, 3, 4, 5];
let zero = "0".to_string();
let result = numbers.iter().fold(zero, |acc, &x| {
format!("({acc} + {x})")
});
assert_eq!(result, "(((((0 + 1) + 2) + 3) + 4) + 5)");Itâs common for people who havenât 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 i in &numbers {
result = result + i;
}
let result2 = numbers.iter().fold(0, |acc, &x| acc + x);
assert_eq!(result, result2);Reduces the elements to a single one, by repeatedly applying a reducing operation.
If the iterator is empty, returns None; otherwise, returns the result of the reduction.
The reducing function is a closure with two arguments: an âaccumulatorâ, and an element. For iterators with at least one element, this is the same as fold() with the first element of the iterator as the initial accumulator value, folding every subsequent element into it.
let reduced: i32 = (1..10).reduce(|acc, e| acc + e).unwrap_or(0);
assert_eq!(reduced, 45);
let folded: i32 = (1..10).fold(0, |acc, e| acc + e);
assert_eq!(reduced, folded);iterator_try_reduce #87053)
Reduces the elements to a single one by repeatedly applying a reducing operation. If the closure returns a failure, the failure is propagated back to the caller immediately.
The return type of this method depends on the return type of the closure. If the closure returns Result<Self::Item, E>, then this function will return Result<Option<Self::Item>, E>. If the closure returns Option<Self::Item>, then this function will return Option<Option<Self::Item>>.
When called on an empty iterator, this function will return either Some(None) or Ok(None) depending on the type of the provided closure.
For iterators with at least one element, this is essentially the same as calling try_fold() with the first element of the iterator as the initial accumulator value.
Safely calculate the sum of a series of numbers:
#![feature(iterator_try_reduce)]
let numbers: Vec<usize> = vec![10, 20, 5, 23, 0];
let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y));
assert_eq!(sum, Some(Some(58)));Determine when a reduction short circuited:
#![feature(iterator_try_reduce)]
let numbers = vec![1, 2, 3, usize::MAX, 4, 5];
let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y));
assert_eq!(sum, None);Determine when a reduction was not performed because there are no elements:
#![feature(iterator_try_reduce)]
let numbers: Vec<usize> = Vec::new();
let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y));
assert_eq!(sum, Some(None));Use a Result instead of an Option:
#![feature(iterator_try_reduce)]
let numbers = vec!["1", "2", "3", "4", "5"];
let max: Result<Option<_>, <usize as std::str::FromStr>::Err> =
numbers.into_iter().try_reduce(|x, y| {
if x.parse::<usize>()? > y.parse::<usize>()? { Ok(x) } else { Ok(y) }
});
assert_eq!(max, Ok(Some("5")));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.
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));
assert_eq!(iter.next(), Some(&3));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.
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));
assert_eq!(iter.next(), Some(&2));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.
If you need the index of the element, see position().
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));
assert_eq!(iter.next(), Some(&3));Note that iter.find(f) is equivalent to iter.filter(f).next().
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().
let a = ["lol", "NaN", "2", "5"];
let first_number = a.iter().find_map(|s| s.parse().ok());
assert_eq!(first_number, Some(2));try_find #63178)
Applies function to the elements of iterator and returns the first true result or the first error.
The return type of this method depends on the return type of the closure. If you return Result<bool, E> from the closure, youâll get a Result<Option<Self::Item>, E>. If you return Option<bool> from the closure, youâll get an Option<Option<Self::Item>>.
#![feature(try_find)]
let a = ["1", "2", "lol", "NaN", "5"];
let is_my_num = |s: &str, search: i32| -> Result<bool, std::num::ParseIntError> {
Ok(s.parse::<i32>()? == search)
};
let result = a.iter().try_find(|&&s| is_my_num(s, 2));
assert_eq!(result, Ok(Some(&"2")));
let result = a.iter().try_find(|&&s| is_my_num(s, 5));
assert!(result.is_err());This also supports other types which implement Try, not just Result.
#![feature(try_find)]
use std::num::NonZero;
let a = [3, 5, 7, 4, 9, 0, 11u32];
let result = a.iter().try_find(|&&x| NonZero::new(x).map(|y| y.is_power_of_two()));
assert_eq!(result, Some(Some(&4)));
let result = a.iter().take(3).try_find(|&&x| NonZero::new(x).map(|y| y.is_power_of_two()));
assert_eq!(result, Some(None));
let result = a.iter().rev().try_find(|&&x| NonZero::new(x).map(|y| y.is_power_of_two()));
assert_eq!(result, None);Searches for an element in an iterator, returning its index.
position() takes a closure that returns true or false. It applies this closure to each element of the iterator, and if one of them returns true, then position() returns Some(index). If all of them return false, it returns None.
position() is short-circuiting; in other words, it will stop processing as soon as it finds a true.
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.
This function might panic if the iterator has more than usize::MAX non-matching elements.
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));
assert_eq!(iter.next(), Some(&3));
assert_eq!(iter.position(|&x| x == 4), Some(0));
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.
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, 4];
let mut iter = a.iter();
assert_eq!(iter.rposition(|&x| x >= 2), Some(3));
assert_eq!(iter.next(), Some(&-1));
assert_eq!(iter.next_back(), Some(&3));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.
Note that f32/f64 doesnât implement Ord due to NaN being incomparable. You can work around this by using Iterator::reduce:
assert_eq!(
[2.4, f32::NAN, 1.3]
.into_iter()
.reduce(f32::max)
.unwrap_or(0.),
2.4
);let a = [1, 2, 3];
let b: Vec<u32> = Vec::new();
assert_eq!(a.iter().max(), Some(&3));
assert_eq!(b.iter().max(), None);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.
Note that f32/f64 doesnât implement Ord due to NaN being incomparable. You can work around this by using Iterator::reduce:
assert_eq!(
[2.4, f32::NAN, 1.3]
.into_iter()
.reduce(f32::min)
.unwrap_or(0.),
1.3
);let a = [1, 2, 3];
let b: Vec<u32> = Vec::new();
assert_eq!(a.iter().min(), Some(&1));
assert_eq!(b.iter().min(), None);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.
let a = [-3_i32, 0, 1, 5, -10];
assert_eq!(*a.iter().max_by_key(|x| x.abs()).unwrap(), -10);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.
let a = [-3_i32, 0, 1, 5, -10];
assert_eq!(*a.iter().max_by(|x, y| x.cmp(y)).unwrap(), 5);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.
let a = [-3_i32, 0, 1, 5, -10];
assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0);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.
let a = [-3_i32, 0, 1, 5, -10];
assert_eq!(*a.iter().min_by(|x, y| x.cmp(y)).unwrap(), -10);Reverses an iteratorâs 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 DoubleEndedIterators.
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);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.
let a = [(1, 2), (3, 4), (5, 6)];
let (left, right): (Vec<_>, Vec<_>) = a.iter().cloned().unzip();
assert_eq!(left, [1, 3, 5]);
assert_eq!(right, [2, 4, 6]);
let a = [(1, (2, 3)), (4, (5, 6))];
let (x, (y, z)): (Vec<_>, (Vec<_>, Vec<_>)) = a.iter().cloned().unzip();
assert_eq!(x, [1, 4]);
assert_eq!(y, [2, 5]);
assert_eq!(z, [3, 6]);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.
let a = [1, 2, 3];
let v_copied: Vec<_> = a.iter().copied().collect();
let v_map: Vec<_> = a.iter().map(|&x| x).collect();
assert_eq!(v_copied, vec![1, 2, 3]);
assert_eq!(v_map, vec![1, 2, 3]);Creates an iterator which clones all of its elements.
This is useful when you have an iterator over &T, but you need an iterator over T.
There is no guarantee whatsoever about the clone method actually being called or optimized away. So code should not depend on either.
Basic usage:
let a = [1, 2, 3];
let v_cloned: Vec<_> = a.iter().cloned().collect();
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]);To get the best performance, try to clone late:
let a = [vec![0_u8, 1, 2], vec![3, 4], vec![23]];
let slower: Vec<_> = a.iter().cloned().filter(|s| s.len() == 1).collect();
assert_eq!(&[vec![23]], &slower[..]);
let faster: Vec<_> = a.iter().filter(|s| s.len() == 1).cloned().collect();
assert_eq!(&[vec![23]], &faster[..]);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. Note that in case the original iterator is empty, the resulting iterator will also be empty.
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));iter_array_chunks #100450)
Returns an iterator over N elements of the iterator at a time.
The chunks do not overlap. If N does not divide the length of the iterator, then the last up to N-1 elements will be omitted and can be retrieved from the .into_remainder() function of the iterator.
Panics if N is zero.
Basic usage:
#![feature(iter_array_chunks)]
let mut iter = "lorem".chars().array_chunks();
assert_eq!(iter.next(), Some(['l', 'o']));
assert_eq!(iter.next(), Some(['r', 'e']));
assert_eq!(iter.next(), None);
assert_eq!(iter.into_remainder().unwrap().as_slice(), &['m']);#![feature(iter_array_chunks)]
let data = [1, 1, 2, -2, 6, 0, 3, 1];
for [x, y, z] in data.iter().array_chunks() {
assert_eq!(x + y + z, 4);
}Sums the elements of an iterator.
Takes each element, adds them together, and returns the result.
An empty iterator returns the additive identity (âzeroâ) of the type, which is 0 for integers and -0.0 for floats.
sum() can be used to sum any type implementing Sum, including Option and Result.
When calling sum() and a primitive integer type is being returned, this method will panic if the computation overflows and debug assertions are enabled.
let a = [1, 2, 3];
let sum: i32 = a.iter().sum();
assert_eq!(sum, 6);
let b: Vec<f32> = vec![];
let sum: f32 = b.iter().sum();
assert_eq!(sum, -0.0_f32);Iterates over the entire iterator, multiplying all the elements
An empty iterator returns the one value of the type.
product() can be used to multiply any type implementing Product, including Option and Result.
When calling product() and a primitive integer type is being returned, method will panic if the computation overflows and debug assertions are enabled.
fn factorial(n: u32) -> u32 {
(1..=n).product()
}
assert_eq!(factorial(0), 1);
assert_eq!(factorial(1), 1);
assert_eq!(factorial(5), 120);Lexicographically compares the elements of this Iterator with those of another.
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);iter_order_by #64295)
Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function.
#![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);Lexicographically compares the PartialOrd elements of this Iterator with those of another. The comparison works like short-circuit evaluation, returning a result without comparing the remaining elements. As soon as an order can be determined, the evaluation stops and a result is returned.
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));For floating-point numbers, NaN does not have a total order and will result in None when compared:
assert_eq!([f64::NAN].iter().partial_cmp([1.].iter()), None);The results are determined by the order of evaluation.
use std::cmp::Ordering;
assert_eq!([1.0, f64::NAN].iter().partial_cmp([2.0, f64::NAN].iter()), Some(Ordering::Less));
assert_eq!([2.0, f64::NAN].iter().partial_cmp([1.0, f64::NAN].iter()), Some(Ordering::Greater));
assert_eq!([f64::NAN, 1.0].iter().partial_cmp([f64::NAN, 2.0].iter()), None);iter_order_by #64295)
Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function.
#![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)
);Determines if the elements of this Iterator are equal to those of another.
assert_eq!([1].iter().eq([1].iter()), true);
assert_eq!([1].iter().eq([1, 2].iter()), false);iter_order_by #64295)
Determines if the elements of this Iterator are equal to those of another with respect to the specified equality function.
#![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));Determines if the elements of this Iterator are not equal to those of another.
assert_eq!([1].iter().ne([1].iter()), false);
assert_eq!([1].iter().ne([1, 2].iter()), true);Determines if the elements of this Iterator are lexicographically less than those of another.
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);
assert_eq!([1, 2].iter().lt([1, 2].iter()), false);Determines if the elements of this Iterator are lexicographically less or equal to those of another.
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);
assert_eq!([1, 2].iter().le([1, 2].iter()), true);Determines if the elements of this Iterator are lexicographically greater than those of another.
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);
assert_eq!([1, 2].iter().gt([1, 2].iter()), false);Determines if the elements of this Iterator are lexicographically greater than or equal to those of another.
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);
assert_eq!([1, 2].iter().ge([1, 2].iter()), true);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.
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, f32::NAN].iter().is_sorted());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 whether two elements are to be considered in sorted order.
assert!([1, 2, 2, 9].iter().is_sorted_by(|a, b| a <= b));
assert!(![1, 2, 2, 9].iter().is_sorted_by(|a, b| a < b));
assert!([0].iter().is_sorted_by(|a, b| true));
assert!([0].iter().is_sorted_by(|a, b| false));
assert!(std::iter::empty::<i32>().is_sorted_by(|a, b| false));
assert!(std::iter::empty::<i32>().is_sorted_by(|a, b| true));Checks if the elements of this iterator are sorted using the given key extraction function.
Instead of comparing the iteratorâs elements directly, this function compares the keys of the elements, as determined by f. Apart from that, itâs equivalent to is_sorted; see its documentation for more information.
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()));RetroSearch is an open source project built by @garambo | Open a GitHub Issue
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