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 default
error[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 warning
error: could not compile `foo` (bin "foo") due to previous error; 1 warning emitted