1.28.0[−][src]Function core::iter::repeat_with
ⓘImportant traits for RepeatWith<F>
pub fn repeat_with<A, F: FnMut() -> A>(repeater: F) -> RepeatWith<F>
Creates a new iterator that repeats elements of type A
endlessly by
applying the provided closure, the repeater, F: FnMut() -> A
.
The repeat_with()
function calls the repeater over and over again.
Infinite iterators like repeat_with()
are often used with adapters like
take
, in order to make them finite.
If the element type of the iterator you need implements Clone
, and
it is OK to keep the source element in memory, you should instead use
the repeat
function.
An iterator produced by repeat_with()
is not a DoubleEndedIterator
.
If you need repeat_with()
to return a DoubleEndedIterator
,
please open a GitHub issue explaining your use case.
Examples
Basic usage:
use std::iter; // let's assume we have some value of a type that is not `Clone` // or which don't want to have in memory just yet because it is expensive: #[derive(PartialEq, Debug)] struct Expensive; // a particular value forever: let mut things = iter::repeat_with(|| Expensive); assert_eq!(Some(Expensive), things.next()); assert_eq!(Some(Expensive), things.next()); assert_eq!(Some(Expensive), things.next()); assert_eq!(Some(Expensive), things.next()); assert_eq!(Some(Expensive), things.next());Run
Using mutation and going finite:
use std::iter; // From the zeroth to the third power of two: let mut curr = 1; let mut pow2 = iter::repeat_with(|| { let tmp = curr; curr *= 2; tmp }) .take(4); assert_eq!(Some(1), pow2.next()); assert_eq!(Some(2), pow2.next()); assert_eq!(Some(4), pow2.next()); assert_eq!(Some(8), pow2.next()); // ... and now we're done assert_eq!(None, pow2.next());Run