error[E0277]: the size for values of type `(dyn I + 'static)` cannot be known at compilation time --> $DIR/issue-5035-2.rs:4:8 | LL | fn foo(_x: K) {} | ^^ doesn't have a size known at compile-time | = help: the trait `Sized` is not implemented for `(dyn I + 'static)` = help: unsized fn params are gated as an unstable feature help: function arguments must have a statically known size, borrowed types always have a known size | LL | fn foo(_x: &K) {} | + error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.