error[E0277]: the size for values of type `(dyn A + 'static)` cannot be known at compilation time --> $DIR/issue-5883.rs:8:5 | LL | r: dyn A + 'static | ^ doesn't have a size known at compile-time | = help: the trait `Sized` is not implemented for `(dyn A + 'static)` = help: unsized fn params are gated as an unstable feature help: you can use `impl Trait` as the argument type | LL | r: impl A + 'static | ~~~~ help: function arguments must have a statically known size, borrowed types always have a known size | LL | r: &dyn A + 'static | + error[E0277]: the size for values of type `(dyn A + 'static)` cannot be known at compilation time --> $DIR/issue-5883.rs:9:6 | LL | ) -> Struct { | ^^^^^^ doesn't have a size known at compile-time LL | Struct { r: r } | --------------- this returned value is of type `Struct` | = help: within `Struct`, the trait `Sized` is not implemented for `(dyn A + 'static)` note: required because it appears within the type `Struct` --> $DIR/issue-5883.rs:3:8 | LL | struct Struct { | ^^^^^^ = note: the return type of a function must have a statically known size error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0277`.