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