src/librustc_error_codes/error_codes/E0698.md

   1 When using generators (or async) all type variables must be bound so a
   2 generator can be constructed.
   3
   4 Erroneous code example:
   5
   6 ```edition2018,compile-fail,E0698
   7 async fn bar<T>() -> () {}
   8
   9 async fn foo() {
  10     bar().await; // error: cannot infer type for `T`
  11 }
  12 ```
  13
  14 In the above example `T` is unknowable by the compiler.
  15 To fix this you must bind `T` to a concrete type such as `String`
  16 so that a generator can then be constructed:
  17
  18 ```edition2018
  19 async fn bar<T>() -> () {}
  20
  21 async fn foo() {
  22     bar::<String>().await;
  23     //   ^^^^^^^^ specify type explicitly
  24 }
  25 ```