error[E0053]: method `foo` has an incompatible generic parameter for trait `Foo` --> $DIR/generics-mismatch.rs:13:18 | LL | trait Foo { | --- LL | async fn foo(); | - expected type parameter ... LL | impl Foo for () { | --------------- LL | async fn foo() {} | ^^^^^^^^^^^^^^ found const parameter of type `usize` error: aborting due to previous error For more information about this error, try `rustc --explain E0053`.