Error code E0698

Note: this error code is no longer emitted by the compiler.

When using coroutines (or async) all type variables must be bound so a coroutine can be constructed.

Erroneous code example:

#![allow(unused)]
fn main() {
async fn bar<T>() -> () {}

async fn foo() {
    bar().await; // error: cannot infer type for `T`
}
}

In the above example T is unknowable by the compiler. To fix this you must bind T to a concrete type such as String so that a coroutine can then be constructed:

#![allow(unused)]
fn main() {
async fn bar<T>() -> () {}

async fn foo() {
    bar::<String>().await;
    //   ^^^^^^^^ specify type explicitly
}
}