#![feature(box_syntax)] trait Foo { fn f(&self); } struct Bar { x: isize, } impl Drop for Bar { fn drop(&mut self) {} } impl Foo for Bar { fn f(&self) { println!("hi"); } } fn main() { let x = box Bar { x: 10 }; let y: Box = x as Box; let _z = y.clone(); //~ ERROR no method named `clone` found }