error[E0038]: the trait `Bar` cannot be made into an object --> $DIR/issue-18959.rs:11:11 | LL | pub trait Foo { fn foo(&self, ext_thing: &T); } | --- method `foo` has generic type parameters ... LL | fn foo(b: &dyn Bar) { | ^^^^^^^^ the trait `Bar` cannot be made into an object error: aborting due to previous error For more information about this error, try `rustc --explain E0038`.