Code shared from the Rust Playground

playground.rs

use core::future::Future;

async fn foo() -> u64 {
    10
}

async fn bar(x: impl Future<Output = u64>) {
    println!("{}", x.await);
}

fn baz() -> impl Future<Output = u64> {
    let mut x: Vec<_> = vec![foo(), foo()];
    let y: Vec<Box<dyn Future<Output = u64>>> = x.iter().map(|f| f.boxed()).collect();
    x.pop().unwrap()
}

fn main() {
    use futures::executor::block_on;

    block_on(bar(foo()))
}