use async_std::prelude::*;#[async_std::main]async fn main() {    let a = async { 1u8 };    let b = async { 2u8 };    assert_eq!(a.join(b).await, (1u8, 2u8))}

warning: unused import: `async_std::prelude::*` --> src/main.rs:1:5  |1 | use async_std::prelude::*;  |     ^^^^^^^^^^^^^^^^^^^^^  |  = note: `#[warn(unused_imports)]` on by defaulterror[E0599]: no method named `join` found for `async` block `{async block@src/main.rs:5:13: 5:26}` in the current scope --> src/main.rs:7:18  |7 |     assert_eq!(a.join(b).await, (1u8, 2u8))  |                  ^^^^ method not found in `{async block@src/main.rs:5:13: 5:26}`For more information about this error, try `rustc --explain E0599`.warning: `foo` (bin "foo") generated 1 warningerror: could not compile `foo` (bin "foo") due to previous error; 1 warning emitted