Function futures_util::stream::repeat_with [−][src]
pub fn repeat_with<A, F: FnMut() -> A>(repeater: F) -> RepeatWith<F>
Creates a new stream 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 stream like repeat_with()
are often used with adapters like
[stream.take()
], in order to make them finite.
If the element type of the stream you need implements Clone
, and
it is OK to keep the source element in memory, you should instead use
the [stream.repeat()
] function.
Examples
Basic usage:
use futures::stream::{self, StreamExt}; // 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 = stream::repeat_with(|| Expensive); assert_eq!(Some(Expensive), things.next().await); assert_eq!(Some(Expensive), things.next().await); assert_eq!(Some(Expensive), things.next().await);
Using mutation and going finite:
use futures::stream::{self, StreamExt}; // From the zeroth to the third power of two: let mut curr = 1; let mut pow2 = stream::repeat_with(|| { let tmp = curr; curr *= 2; tmp }) .take(4); assert_eq!(Some(1), pow2.next().await); assert_eq!(Some(2), pow2.next().await); assert_eq!(Some(4), pow2.next().await); assert_eq!(Some(8), pow2.next().await); // ... and now we're done assert_eq!(None, pow2.next().await);