error[E0277]: the size for values of type `<Self as std::ops::Deref>::Target` cannot be known at compilation time --> $DIR/issue-42312.rs:4:12 | LL | fn baz(_: Self::Target) where Self: Deref {} | ^ - help: consider further restricting the associated type: `, <Self as std::ops::Deref>::Target: std::marker::Sized` | | | doesn't have a size known at compile-time | = help: the trait `std::marker::Sized` is not implemented for `<Self as std::ops::Deref>::Target` = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait> = note: all function arguments must have a statically known size = help: unsized locals are gated as an unstable feature error[E0277]: the size for values of type `(dyn std::string::ToString + 'static)` cannot be known at compilation time --> $DIR/issue-42312.rs:8:10 | LL | pub fn f(_: dyn ToString) {} | ^ doesn't have a size known at compile-time | = help: the trait `std::marker::Sized` is not implemented for `(dyn std::string::ToString + 'static)` = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait> = note: all function arguments must have a statically known size = help: unsized locals are gated as an unstable feature error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0277`.