futures/src/stream.rs


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//! Create asynchronous streams of data.
use futures::channel::mpsc;
use futures::never::Never;
use futures::stream::{self, Stream, StreamExt};

use std::future::Future;

/// Creates a new [`Stream`] that produces the items sent from a [`Future`]
/// to the [`mpsc::Sender`] provided to the closure.
///
/// This is a more ergonomic [`stream::unfold`], which allows you to go
/// from the "world of futures" to the "world of streams" by simply looping
/// and publishing to an async channel from inside a [`Future`].
pub fn channel<T, F>(
    size: usize,
    f: impl FnOnce(mpsc::Sender<T>) -> F,
) -> impl Stream<Item = T>
where
    F: Future<Output = Never>,
{
    let (sender, receiver) = mpsc::channel(size);

    let runner = stream::once(f(sender)).map(|_| unreachable!());

    stream::select(receiver, runner)
}