error[E0038]: the trait `issue_3907::Foo` cannot be made into an object --> $DIR/issue-3907-2.rs:11:12 | LL | fn bar(_x: Foo) {} | ^^^ `issue_3907::Foo` 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/auxiliary/issue-3907.rs:2:8 | LL | fn bar(); | ^^^ the trait cannot be made into an object because associated function `bar` has no `self` parameter error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0038`.