This crate gives Streams a reduce function that is similar to fold but without an initial value. The function returns a Future containing None if the stream is empty and Some(value) otherwise.

Based on David Tolnay's reduce crate for iterators.

Examples

use stream_reduce::Reduce;
use futures::stream;

# futures::executor::block_on(
async {
    // Reduce a non-empty stream into Some(value)
    let v = vec![1usize, 2, 3, 4, 5];
    let sum = stream::iter(v).reduce(|a, b| async move { a + b }).await;
    assert_eq!(Some(15), sum);

    // Reduce an empty stream into None
    let v = Vec::<usize>::new();
    let product = stream::iter(v).reduce(|a, b| async move { a * b }).await;
    assert_eq!(None, product);
}
# )