#![feature(unsized_locals)] //~^ WARN the feature `unsized_locals` is incomplete pub trait Foo { fn foo(self) -> String where Self: Sized; } struct A; impl Foo for A { fn foo(self) -> String { format!("hello") } } fn main() { let x = *(Box::new(A) as Box); x.foo(); //~^ERROR the `foo` method cannot be invoked on a trait object }