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> ⓘ
where Self: Sized { ... }
fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> ⓘ
where Self: Sized,
U: IntoIterator<Item = Self::Item> { ... }
fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> ⓘ
where Self: Sized,
U: IntoIterator { ... }
fn intersperse(self, separator: Self::Item) -> Intersperse<Self> ⓘ
where Self: Sized,
Self::Item: Clone { ... }
fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G> ⓘ
where Self: Sized,
G: FnMut() -> Self::Item { ... }
fn map<B, F>(self, f: F) -> Map<Self, F> ⓘ
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> ⓘ
where Self: Sized,
P: FnMut(&Self::Item) -> bool { ... }
fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> ⓘ
where Self: Sized,
F: FnMut(Self::Item) -> Option<B> { ... }
fn enumerate(self) -> Enumerate<Self> ⓘ
where Self: Sized { ... }
fn peekable(self) -> Peekable<Self> ⓘ
where Self: Sized { ... }
fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> ⓘ
where Self: Sized,
P: FnMut(&Self::Item) -> bool { ... }
fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> ⓘ
where Self: Sized,
P: FnMut(&Self::Item) -> bool { ... }
fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> ⓘ
where Self: Sized,
P: FnMut(Self::Item) -> Option<B> { ... }
fn skip(self, n: usize) -> Skip<Self> ⓘ
where Self: Sized { ... }
fn take(self, n: usize) -> Take<Self> ⓘ
where Self: Sized { ... }
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> { ... }
fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> ⓘ
where Self: Sized,
U: IntoIterator,
F: FnMut(Self::Item) -> U { ... }
fn flatten(self) -> Flatten<Self> ⓘ
where Self: Sized,
Self::Item: IntoIterator { ... }
fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N> ⓘ
where Self: Sized,
F: FnMut(&[Self::Item; N]) -> R { ... }
fn fuse(self) -> Fuse<Self> ⓘ
where Self: Sized { ... }
fn inspect<F>(self, f: F) -> Inspect<Self, F> ⓘ
where Self: Sized,
F: FnMut(&Self::Item) { ... }
fn by_ref(&mut self) -> &mut Self
where Self: Sized { ... }
fn collect<B: FromIterator<Self::Item>>(self) -> B
where Self: Sized { ... }
fn try_collect<B>(
&mut self,
) -> <Self::Item::Residual as Residual<B>>::TryType
where Self: Sized,
Self::Item: Try<Residual: Residual<B>>,
B: FromIterator<<Self::Item as Try>::Output> { ... }
fn collect_into<E: Extend<Self::Item>>(self, collection: &mut E) -> &mut E
where 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: 'a, P>(self, predicate: P) -> usize
where 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::Residual as Residual<Option<R::Output>>>::TryType
where Self: Sized,
R: Try<Output = Self::Item, 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::Residual as Residual<Option<Self::Item>>>::TryType
where Self: Sized,
R: Try<Output = bool, 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: Ord, F>(self, f: F) -> Option<Self::Item>
where 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: Ord, F>(self, f: F) -> Option<Self::Item>
where 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> ⓘ
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> ⓘ
where Self: Sized + Iterator<Item = &'a T>,
T: Copy + 'a { ... }
fn cloned<'a, T>(self) -> Cloned<Self> ⓘ
where Self: Sized + Iterator<Item = &'a T>,
T: Clone + 'a { ... }
fn cycle(self) -> Cycle<Self> ⓘ
where Self: Sized + Clone { ... }
fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N> ⓘ
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::Item) -> Ordering { ... }
fn partial_cmp<I>(self, other: I) -> Option<Ordering>
where I: IntoIterator,
Self::Item: PartialOrd<I::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::Item) -> Option<Ordering> { ... }
fn eq<I>(self, other: I) -> bool
where I: IntoIterator,
Self::Item: PartialEq<I::Item>,
Self: Sized { ... }
fn eq_by<I, F>(self, other: I, eq: F) -> bool
where Self: Sized,
I: IntoIterator,
F: FnMut(Self::Item, I::Item) -> bool { ... }
fn ne<I>(self, other: I) -> bool
where I: IntoIterator,
Self::Item: PartialEq<I::Item>,
Self: Sized { ... }
fn lt<I>(self, other: I) -> bool
where I: IntoIterator,
Self::Item: PartialOrd<I::Item>,
Self: Sized { ... }
fn le<I>(self, other: I) -> bool
where I: IntoIterator,
Self::Item: PartialOrd<I::Item>,
Self: Sized { ... }
fn gt<I>(self, other: I) -> bool
where I: IntoIterator,
Self::Item: PartialOrd<I::Item>,
Self: Sized { ... }
fn ge<I>(self, other: I) -> bool
where I: IntoIterator,
Self::Item: PartialOrd<I::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 { ... }
}
Expand description
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
.
Required Associated Types§
Required Methods§
1.0.0 · sourcefn next(&mut self) -> Option<Self::Item>
fn next(&mut self) -> Option<Self::Item>
Advances the iterator and returns the next value.
Returns None
when iteration is finished. Individual iterator
implementations may choose to resume iteration, and so calling next()
again may or may not eventually start returning Some(Item)
again at some
point.
§Examples
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());
Provided Methods§
sourcefn next_chunk<const N: usize>(
&mut self,
) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>where
Self: Sized,
🔬This is a nightly-only experimental API. (iter_next_chunk
#98326)
fn next_chunk<const N: usize>(
&mut self,
) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>where
Self: Sized,
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.
§Examples
Basic usage:
#![feature(iter_next_chunk)]
let mut iter = "lorem".chars();
assert_eq!(iter.next_chunk().unwrap(), ['l', 'o']); // N is inferred as 2
assert_eq!(iter.next_chunk().unwrap(), ['r', 'e', 'm']); // N is inferred as 3
assert_eq!(iter.next_chunk::<4>().unwrap_err().as_slice(), &[]); // N is explicitly 4
Split a string and get the first three items.
1.0.0 · sourcefn size_hint(&self) -> (usize, Option<usize>)
fn size_hint(&self) -> (usize, Option<usize>)
Returns the bounds on the remaining length of the iterator.
Specifically, size_hint()
returns a tuple where the first element
is the lower bound, and the second element is the upper bound.
The second half of the tuple that is returned is an Option<usize>
.
A None
here means that either there is no known upper bound, or the
upper bound is larger than usize
.
§Implementation notes
It is not enforced that an iterator implementation yields the declared number of elements. A buggy iterator may yield less than the lower bound or more than the upper bound of elements.
size_hint()
is primarily intended to be used for optimizations such as
reserving space for the elements of the iterator, but must not be
trusted to e.g., omit bounds checks in unsafe code. An incorrect
implementation of size_hint()
should not lead to memory safety
violations.
That said, the implementation should provide a correct estimation, because otherwise it would be a violation of the trait’s protocol.
The default implementation returns (0, None)
which is correct for any
iterator.
§Examples
Basic usage:
let a = [1, 2, 3];
let 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:
// The even numbers in the range of zero to nine.
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:
1.0.0 · sourcefn count(self) -> usizewhere
Self: Sized,
fn count(self) -> usizewhere
Self: Sized,
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.
§Overflow Behavior
The method does no guarding against overflows, so counting elements of
an iterator with more than usize::MAX
elements either produces the
wrong result or panics. If debug assertions are enabled, a panic is
guaranteed.
§Panics
This function might panic if the iterator has more than usize::MAX
elements.
§Examples
1.0.0 · sourcefn last(self) -> Option<Self::Item>where
Self: Sized,
fn last(self) -> Option<Self::Item>where
Self: Sized,
sourcefn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>>
🔬This is a nightly-only experimental API. (iter_advance_by
#77404)
fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>>
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.
§Examples
#![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())); // only `&4` was skipped
1.0.0 · sourcefn nth(&mut self, n: usize) -> Option<Self::Item>
fn nth(&mut self, n: usize) -> Option<Self::Item>
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.
§Examples
Basic usage:
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:
1.28.0 · sourcefn step_by(self, step: usize) -> StepBy<Self> ⓘwhere
Self: Sized,
fn step_by(self, step: usize) -> StepBy<Self> ⓘwhere
Self: Sized,
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)
, …, 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
}
§Panics
The method will panic if the given step is 0
.
§Examples
1.0.0 · sourcefn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> ⓘ
fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> ⓘ
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. 🔗
once
is commonly used to adapt a single value into a chain of
other kinds of iteration.
§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:
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>
:
1.0.0 · sourcefn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> ⓘwhere
Self: Sized,
U: IntoIterator,
fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> ⓘwhere
Self: Sized,
U: IntoIterator,
‘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 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 ‘undo’ the result of zipping up two iterators, see unzip
.
§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:
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:
sourcefn intersperse(self, separator: Self::Item) -> Intersperse<Self> ⓘ
🔬This is a nightly-only experimental API. (iter_intersperse
#79524)
fn intersperse(self, separator: Self::Item) -> Intersperse<Self> ⓘ
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
.
§Examples
Basic usage:
#![feature(iter_intersperse)]
let mut a = [0, 1, 2].iter().intersperse(&100);
assert_eq!(a.next(), Some(&0)); // The first element from `a`.
assert_eq!(a.next(), Some(&100)); // The separator.
assert_eq!(a.next(), Some(&1)); // The next element from `a`.
assert_eq!(a.next(), Some(&100)); // The separator.
assert_eq!(a.next(), Some(&2)); // The last element from `a`.
assert_eq!(a.next(), None); // The iterator is finished.
intersperse
can be very useful to join an iterator’s items using a common element:
sourcefn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G> ⓘ
🔬This is a nightly-only experimental API. (iter_intersperse
#79524)
fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G> ⓘ
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 iterator’s item implements Clone
, it may be easier to use
intersperse
.
§Examples
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))); // The first element from `v`.
assert_eq!(it.next(), Some(NotClone(99))); // The separator.
assert_eq!(it.next(), Some(NotClone(1))); // The next element from `v`.
assert_eq!(it.next(), Some(NotClone(99))); // The separator.
assert_eq!(it.next(), Some(NotClone(2))); // The last element from `v`.
assert_eq!(it.next(), None); // The iterator is finished.
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();
// The closure mutably borrows its context to generate an item.
let mut happy_emojis = [" ❤️ ", " 😀 "].iter().copied();
let separator = || happy_emojis.next().unwrap_or(" 🦀 ");
let result = src.intersperse_with(separator).collect::<String>();
assert_eq!(result, "Hello ❤️ to 😀 all 🦀 people 🦀 !!");
1.0.0 · sourcefn map<B, F>(self, f: F) -> Map<Self, F> ⓘ
fn map<B, F>(self, f: F) -> Map<Self, F> ⓘ
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()
.
§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()
:
1.21.0 · sourcefn for_each<F>(self, f: F)
fn for_each<F>(self, f: 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 adapters like Chain
.
§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:
1.0.0 · sourcefn filter<P>(self, predicate: P) -> Filter<Self, P> ⓘ
fn filter<P>(self, predicate: P) -> Filter<Self, P> ⓘ
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
.
§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.
Note that iter.filter(f).next()
is equivalent to iter.find(f)
.
1.0.0 · sourcefn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> ⓘ
fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> ⓘ
Creates an iterator that both filters and maps.
The returned iterator yields only the value
s 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
.
§Examples
Basic usage:
1.0.0 · sourcefn enumerate(self) -> Enumerate<Self> ⓘwhere
Self: Sized,
fn enumerate(self) -> Enumerate<Self> ⓘwhere
Self: Sized,
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
.
§Examples
1.0.0 · sourcefn peekable(self) -> Peekable<Self> ⓘwhere
Self: Sized,
fn peekable(self) -> Peekable<Self> ⓘwhere
Self: Sized,
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.
§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);
Using peek_mut
to mutate the next item without advancing the
iterator:
let xs = [1, 2, 3];
let mut iter = xs.iter().peekable();
// `peek_mut()` lets us see into the future
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);
// put a value into the iterator
*p = &1000;
}
// The value reappears as the iterator continues
assert_eq!(iter.collect::<Vec<_>>(), vec![&1000, &3]);
1.0.0 · sourcefn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> ⓘ
fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> ⓘ
Creates an iterator that skip
s 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()
’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 argument 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);
1.0.0 · sourcefn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> ⓘ
fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> ⓘ
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.
1.57.0 · sourcefn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> ⓘ
fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> ⓘ
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(_)
.
§Examples
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);
Here’s 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<_>>();
// We have more elements which could fit in u32 (4, 5), but `map_while` returned `None` for `-3`
// (as the `predicate` returned `None`) and `collect` stops at the first `None` encountered.
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 wasn’t 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
.
1.0.0 · sourcefn skip(self, n: usize) -> Skip<Self> ⓘwhere
Self: Sized,
fn skip(self, n: usize) -> Skip<Self> ⓘwhere
Self: Sized,
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.
§Examples
1.0.0 · sourcefn take(self, n: usize) -> Take<Self> ⓘwhere
Self: Sized,
fn take(self, n: usize) -> Take<Self> ⓘwhere
Self: Sized,
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.
§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);
If less than n
elements are available,
take
will limit itself to the size of the underlying iterator:
1.0.0 · sourcefn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> ⓘ
fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> ⓘ
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.
§Examples
let a = [1, 2, 3, 4];
let mut iter = a.iter().scan(1, |state, &x| {
// each iteration, we'll multiply the state by the element ...
*state = *state * x;
// ... and terminate if the state exceeds 6
if *state > 6 {
return None;
}
// ... else 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);
1.0.0 · sourcefn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> ⓘ
fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, 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.
§Examples
1.29.0 · sourcefn flatten(self) -> Flatten<Self> ⓘ
fn flatten(self) -> Flatten<Self> ⓘ
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 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 “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.
sourcefn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N> ⓘ
🔬This is a nightly-only experimental API. (iter_map_windows
#87155)
fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N> ⓘ
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 𝑘 − N
+ 1 items (where 𝑘 is the number of
items yielded by self
). If 𝑘 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
Panics if N
is 0. This check will most probably get changed to a
compile time error before this method gets stabilized.
§Examples
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)); // 1 + 3
assert_eq!(it.next(), Some(11)); // 3 + 8
assert_eq!(it.next(), Some(9)); // 8 + 1
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)); // 0.5 <= 1.0
assert_eq!(it.next(), Some(true)); // 1.0 <= 3.5
assert_eq!(it.next(), Some(false)); // 3.5 <= 3.0
assert_eq!(it.next(), Some(true)); // 3.0 <= 8.5
assert_eq!(it.next(), Some(true)); // 8.5 <= 8.5
assert_eq!(it.next(), Some(false)); // 8.5 <= NAN
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;
// yields `0..5` first, then only even numbers since `6..`.
if val < 5 || val % 2 == 0 {
Some(val)
} else {
None
}
}
}
let mut iter = NonFusedIterator::default();
// yields 0..5 first.
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));
// then we can see our iterator going back and forth
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);
// however, with `.map_windows()`, it is fused.
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);
// it will always return `None` after the first time.
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), None);
1.0.0 · sourcefn fuse(self) -> Fuse<Self> ⓘwhere
Self: Sized,
fn fuse(self) -> Fuse<Self> ⓘwhere
Self: Sized,
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.
§Examples
// 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);
1.0.0 · sourcefn inspect<F>(self, f: F) -> Inspect<Self, F> ⓘ
fn inspect<F>(self, f: F) -> Inspect<Self, F> ⓘ
Does 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:
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:
Parsing error: invalid digit found in string
Sum: 3
1.0.0 · sourcefn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
Borrows an iterator, rather than consuming it.
This is useful to allow applying iterator adapters while still retaining ownership of the original iterator.
§Examples
let mut words = ["hello", "world", "of", "Rust"].into_iter();
// Take the first two words.
let hello_world: Vec<_> = words.by_ref().take(2).collect();
assert_eq!(hello_world, vec!["hello", "world"]);
// Collect the rest of the words.
// We can only do this because we used `by_ref` earlier.
let of_rust: Vec<_> = words.collect();
assert_eq!(of_rust, vec!["of", "Rust"]);
1.0.0 · sourcefn collect<B: FromIterator<Self::Item>>(self) -> Bwhere
Self: Sized,
fn collect<B: FromIterator<Self::Item>>(self) -> Bwhere
Self: Sized,
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 char
s,
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 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:
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>
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);
sourcefn try_collect<B>(&mut self) -> <Self::Item::Residual as Residual<B>>::TryType
🔬This is a nightly-only experimental API. (iterator_try_collect
#94047)
fn try_collect<B>(&mut self) -> <Self::Item::Residual as Residual<B>>::TryType
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()
doesn’t 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
doesn’t.
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.
§Examples
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
doesn’t 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]));
sourcefn collect_into<E: Extend<Self::Item>>(self, collection: &mut E) -> &mut Ewhere
Self: Sized,
🔬This is a nightly-only experimental API. (iter_collect_into
#94780)
fn collect_into<E: Extend<Self::Item>>(self, collection: &mut E) -> &mut Ewhere
Self: Sized,
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, it’s called on an iterator.
§Examples
Basic 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]);
1.0.0 · sourcefn partition<B, F>(self, f: F) -> (B, B)
fn partition<B, F>(self, f: F) -> (B, B)
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()
.
§Examples
sourcefn partition_in_place<'a, T: 'a, P>(self, predicate: P) -> usize
🔬This is a nightly-only experimental API. (iter_partition_in_place
#62543)
fn partition_in_place<'a, T: 'a, P>(self, predicate: P) -> usize
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 implementation
The 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()
.
§Examples
sourcefn is_partitioned<P>(self, predicate: P) -> bool
🔬This is a nightly-only experimental API. (iter_is_partitioned
#62544)
fn is_partitioned<P>(self, predicate: P) -> bool
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()
.
§Examples
1.27.0 · sourcefn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
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
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 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));
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));
1.27.0 · sourcefn try_for_each<F, R>(&mut self, f: F) -> R
fn try_for_each<F, R>(&mut self, f: F) -> R
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()
.
§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"));
The ControlFlow
type can be used with this method for the situations
in which you’d use break
and continue
in a normal loop:
1.0.0 · sourcefn fold<B, F>(self, init: B, f: F) -> B
fn fold<B, F>(self, init: B, f: F) -> B
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 ‘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,
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()
.
§Note to Implementors
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.
§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
.
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)");
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:
1.51.0 · sourcefn reduce<F>(self, f: F) -> Option<Self::Item>
fn reduce<F>(self, f: F) -> Option<Self::Item>
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 ‘accumulator’, 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.
§Example
sourcefn try_reduce<R>(
&mut self,
f: impl FnMut(Self::Item, Self::Item) -> R,
) -> <R::Residual as Residual<Option<R::Output>>>::TryType
🔬This is a nightly-only experimental API. (iterator_try_reduce
#87053)
fn try_reduce<R>( &mut self, f: impl FnMut(Self::Item, Self::Item) -> R, ) -> <R::Residual as Residual<Option<R::Output>>>::TryType
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.
§Examples
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:
1.0.0 · sourcefn all<F>(&mut self, f: F) -> bool
fn all<F>(&mut self, f: F) -> bool
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:
Stopping at the first false
:
1.0.0 · sourcefn any<F>(&mut self, f: F) -> bool
fn any<F>(&mut self, f: F) -> bool
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:
Stopping at the first true
:
1.0.0 · sourcefn find<P>(&mut self, predicate: P) -> Option<Self::Item>
fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
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()
.
§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));
Note that iter.find(f)
is equivalent to iter.filter(f).next()
.
1.30.0 · sourcefn find_map<B, F>(&mut self, f: F) -> Option<B>
fn find_map<B, F>(&mut self, f: F) -> Option<B>
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
sourcefn try_find<R>(
&mut self,
f: impl FnMut(&Self::Item) -> R,
) -> <R::Residual as Residual<Option<Self::Item>>>::TryType
🔬This is a nightly-only experimental API. (try_find
#63178)
fn try_find<R>( &mut self, f: impl FnMut(&Self::Item) -> R, ) -> <R::Residual as Residual<Option<Self::Item>>>::TryType
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, you’ll get a Result<Option<Self::Item>, E>
.
If you return Option<bool>
from the closure, you’ll get an Option<Option<Self::Item>>
.
§Examples
#![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);
1.0.0 · sourcefn position<P>(&mut self, predicate: P) -> Option<usize>
fn position<P>(&mut self, predicate: P) -> Option<usize>
Searches for an element in an iterator, returning its index.
position()
takes a closure that returns true
or false
. It applies
this closure to each element of the iterator, and if one of them
returns true
, then position()
returns Some(index)
. If all of
them return false
, it returns None
.
position()
is short-circuiting; in other words, it will stop
processing as soon as it finds a true
.
§Overflow Behavior
The method does no guarding against overflows, so if there are more
than usize::MAX
non-matching elements, it either produces the wrong
result or panics. If debug assertions are enabled, a panic is
guaranteed.
§Panics
This function might panic if the iterator has more than usize::MAX
non-matching elements.
§Examples
Basic usage:
let a = [1, 2, 3];
assert_eq!(a.iter().position(|&x| x == 2), Some(1));
assert_eq!(a.iter().position(|&x| x == 5), None);
Stopping at the first true
:
1.0.0 · sourcefn rposition<P>(&mut self, predicate: P) -> Option<usize>
fn rposition<P>(&mut self, predicate: P) -> Option<usize>
Searches for an element in an iterator from the right, returning its index.
rposition()
takes a closure that returns true
or false
. It applies
this closure to each element of the iterator, starting from the end,
and if one of them returns true
, then rposition()
returns
Some(index)
. If all of them return false
, it returns None
.
rposition()
is short-circuiting; in other words, it will stop
processing as soon as it finds a true
.
§Examples
Basic usage:
let a = [1, 2, 3];
assert_eq!(a.iter().rposition(|&x| x == 3), Some(2));
assert_eq!(a.iter().rposition(|&x| x == 5), None);
Stopping at the first true
:
1.0.0 · sourcefn max(self) -> Option<Self::Item>
fn max(self) -> Option<Self::Item>
1.0.0 · sourcefn min(self) -> Option<Self::Item>
fn min(self) -> Option<Self::Item>
1.6.0 · sourcefn max_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>
fn max_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>
1.15.0 · sourcefn max_by<F>(self, compare: F) -> Option<Self::Item>
fn max_by<F>(self, compare: F) -> Option<Self::Item>
1.6.0 · sourcefn min_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>
fn min_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>
1.15.0 · sourcefn min_by<F>(self, compare: F) -> Option<Self::Item>
fn min_by<F>(self, compare: F) -> Option<Self::Item>
1.0.0 · sourcefn rev(self) -> Rev<Self> ⓘwhere
Self: Sized + DoubleEndedIterator,
fn rev(self) -> Rev<Self> ⓘwhere
Self: Sized + DoubleEndedIterator,
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.
§Examples
1.0.0 · sourcefn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
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
.
§Examples
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]);
// you can also unzip multiple nested tuples at once
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]);
1.36.0 · sourcefn copied<'a, T>(self) -> Copied<Self> ⓘ
fn copied<'a, T>(self) -> Copied<Self> ⓘ
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
1.0.0 · sourcefn cloned<'a, T>(self) -> Cloned<Self> ⓘ
fn cloned<'a, T>(self) -> Cloned<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
.
There is no guarantee whatsoever about the clone
method actually
being called or optimized away. So code should not depend on
either.
§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]);
To get the best performance, try to clone late:
let a = [vec![0_u8, 1, 2], vec![3, 4], vec![23]];
// don't do this:
let slower: Vec<_> = a.iter().cloned().filter(|s| s.len() == 1).collect();
assert_eq!(&[vec![23]], &slower[..]);
// instead call `cloned` late
let faster: Vec<_> = a.iter().filter(|s| s.len() == 1).cloned().collect();
assert_eq!(&[vec![23]], &faster[..]);
1.0.0 · sourcefn cycle(self) -> Cycle<Self> ⓘ
fn cycle(self) -> Cycle<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. Note that in case the
original iterator is empty, the resulting iterator will also be empty.
§Examples
sourcefn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N> ⓘwhere
Self: Sized,
🔬This is a nightly-only experimental API. (iter_array_chunks
#100450)
fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N> ⓘwhere
Self: Sized,
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
Panics if N
is 0.
§Examples
Basic usage:
1.11.0 · sourcefn sum<S>(self) -> S
fn sum<S>(self) -> S
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.
sum()
can be used to sum any type implementing Sum
,
including Option
and Result
.
§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
1.11.0 · sourcefn product<P>(self) -> P
fn product<P>(self) -> P
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
.
§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
1.5.0 · sourcefn cmp<I>(self, other: I) -> Ordering
fn cmp<I>(self, other: I) -> Ordering
Lexicographically compares the elements of this Iterator
with those
of another.
§Examples
sourcefn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering
🔬This is a nightly-only experimental API. (iter_order_by
#64295)
fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering
iter_order_by
#64295)Lexicographically compares the elements of this Iterator
with those
of another with respect to the specified comparison function.
§Examples
#![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);
1.5.0 · sourcefn partial_cmp<I>(self, other: I) -> Option<Ordering>
fn partial_cmp<I>(self, other: I) -> Option<Ordering>
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.
§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));
For floating-point numbers, NaN does not have a total order and will result
in None
when compared:
The results are determined by the order of evaluation.
sourcefn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>
🔬This is a nightly-only experimental API. (iter_order_by
#64295)
fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>
iter_order_by
#64295)Lexicographically compares the elements of this Iterator
with those
of another with respect to the specified comparison function.
§Examples
#![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)
);
sourcefn eq_by<I, F>(self, other: I, eq: F) -> bool
🔬This is a nightly-only experimental API. (iter_order_by
#64295)
fn eq_by<I, F>(self, other: I, eq: F) -> bool
iter_order_by
#64295)1.5.0 · sourcefn lt<I>(self, other: I) -> bool
fn lt<I>(self, other: I) -> bool
Determines if the elements of this Iterator
are lexicographically
less than those of another.
§Examples
1.5.0 · sourcefn le<I>(self, other: I) -> bool
fn le<I>(self, other: I) -> bool
Determines if the elements of this Iterator
are lexicographically
less or equal to those of another.
§Examples
1.5.0 · sourcefn gt<I>(self, other: I) -> bool
fn gt<I>(self, other: I) -> bool
Determines if the elements of this Iterator
are lexicographically
greater than those of another.
§Examples
1.5.0 · sourcefn ge<I>(self, other: I) -> bool
fn ge<I>(self, other: I) -> bool
Determines if the elements of this Iterator
are lexicographically
greater than or equal to those of another.
§Examples
1.83.0 · sourcefn is_sorted(self) -> bool
fn is_sorted(self) -> bool
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
1.83.0 · sourcefn is_sorted_by<F>(self, compare: F) -> bool
fn is_sorted_by<F>(self, compare: F) -> bool
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.
§Examples
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));
1.83.0 · sourcefn is_sorted_by_key<F, K>(self, f: F) -> bool
fn is_sorted_by_key<F, K>(self, f: F) -> bool
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.