2 #![allow(non_camel_case_types)]
3 #![feature(box_syntax)]
6 fn double(self: Box<Self>) -> usize;
9 impl double for usize {
10 fn double(self: Box<usize>) -> usize { *self * 2 }
14 let x: Box<_> = box (box 3usize as Box<dyn double>);
15 assert_eq!(x.double(), 6);