error[E0038]: the trait `Bar` cannot be made into an object --> $DIR/issue-19538.rs:17:15 | LL | let test: &mut dyn Bar = &mut thing; | ^^^^^^^^^^^^ `Bar` cannot be made into an object | note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit --> $DIR/issue-19538.rs:2:8 | LL | fn foo(&self, val: T); | ^^^ ...because method `foo` has generic type parameters ... LL | trait Bar: Foo { } | --- this trait cannot be made into an object... = help: consider moving `foo` to another trait error[E0038]: the trait `Bar` cannot be made into an object --> $DIR/issue-19538.rs:17:30 | LL | let test: &mut dyn Bar = &mut thing; | ^^^^^^^^^^ `Bar` cannot be made into an object | note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit --> $DIR/issue-19538.rs:2:8 | LL | fn foo(&self, val: T); | ^^^ ...because method `foo` has generic type parameters ... LL | trait Bar: Foo { } | --- this trait cannot be made into an object... = help: consider moving `foo` to another trait = note: required for the cast from `&mut Thing` to `&mut dyn Bar` error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0038`.