error[E0308]: mismatched types --> $DIR/issue-74282.rs:8:15 | LL | type Closure = impl Fn() -> u64; | ---------------- the expected opaque type ... LL | Anonymous(|| { | _____---------_^ | | | | | arguments to this struct are incorrect LL | | LL | | 3 LL | | }) | |_____^ expected opaque type, found closure | = note: expected opaque type `Closure` found closure `[closure@$DIR/issue-74282.rs:8:15: 8:17]` = note: no two closures, even if identical, have the same type = help: consider boxing your closure and/or using it as a trait object note: tuple struct defined here --> $DIR/issue-74282.rs:4:8 | LL | struct Anonymous(Closure); | ^^^^^^^^^ error[E0308]: mismatched types --> $DIR/issue-74282.rs:8:5 | LL | / Anonymous(|| { LL | | LL | | 3 LL | | }) | |______^ expected `()`, found `Anonymous` | help: consider using a semicolon here | LL | }); | + help: try adding a return type | LL | fn bop(_: Closure) -> Anonymous { | ++++++++++++ error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0308`.