error[E0277]: the size for values of type `str` cannot be known at compilation time --> $DIR/unsized-ret.rs:10:11 | LL | foo:: str, _>(None, ()); | ^^^^^^^^^^^ doesn't have a size known at compile-time | = help: within `fn() -> str`, the trait `Sized` is not implemented for `str` = note: required because it appears within the type `fn() -> str` note: required by a bound in `foo` --> $DIR/unsized-ret.rs:5:11 | LL | fn foo, T:std::marker::Tuple>(f: Option, t: T) { | ^^^^^ required by this bound in `foo` error[E0277]: the size for values of type `(dyn std::fmt::Display + 'a)` cannot be known at compilation time --> $DIR/unsized-ret.rs:13:11 | LL | foo:: fn(&'a ()) -> (dyn std::fmt::Display + 'a), _>(None, (&(),)); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time | = help: within `for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a)`, the trait `for<'a> Sized` is not implemented for `(dyn std::fmt::Display + 'a)` = note: required because it appears within the type `fn(&()) -> dyn Display` note: required by a bound in `foo` --> $DIR/unsized-ret.rs:5:11 | LL | fn foo, T:std::marker::Tuple>(f: Option, t: T) { | ^^^^^ required by this bound in `foo` error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0277`.