Function tokio_stream::once 
source · pub fn once<T>(value: T) -> Once<T>Expand description
Creates a stream that emits an element exactly once.
The returned stream is immediately ready and emits the provided value once.
Examples
use tokio_stream::{self as stream, StreamExt};
#[tokio::main]
async fn main() {
    // one is the loneliest number
    let mut one = stream::once(1);
    assert_eq!(Some(1), one.next().await);
    // just one, that's all we get
    assert_eq!(None, one.next().await);
}