merging streams in rust / tokio

Question

tokio has a Merge data structure which allows to "merge" two homogeneous streams and forget the provenance.

impl<T, U> Stream for Merge<T, U> where
    T: Stream,
    U: Stream<Item = T::Item>, { ...

Is there an algebraic pointwise tagged union for streams, which from a stream of a and a stream of b , produces a stream of Either ab ?

PS : I guess the answer is no as there is no standard sum type in rust apparently..

Answer 1

I don't think it's provided directly as a method in tokio, but you piece it together very simply yourself. There is no Either type in the Rust standard library but, like most other things, there's a crate for that.

use either::Either; // 0.3.7
use tokio::stream::StreamExt as _;

stream1
    .map(Either::Left)
    .merge(stream2.map(Either::Right))