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);
}
# )