simple_example_select_futures.rs

use futures::{
    pin_mut,
    future::Either,
    future::self,
    executor::block_on,
};


async fn race_tasks() -> usize {
    // These two futures have different types even though their outputs have the same type
    let future1 = async {
        let () = future::pending().await; // will never finish
        1
    };
    let future2 = async { 
        future::ready(2 as usize).await
    };

    // 'select' requires Future + Unpin bounds
    pin_mut!(future1);
    pin_mut!(future2);

    match future::select(future1, future2).await {
        Either::Left((value1, _)) => value1, // `value1` is resolved from `future1`
        // `_` represents `future2`
        Either::Right((value2, _)) => value2, // `value2` is resolved from `future2`
        // `_` represents `future1`
    }
}


fn main() {
    let finished_first = block_on(race_tasks());
    assert!(finished_first == 2);
}