1 // run-pass 2 #![allow(non_camel_case_types)] 3 4 trait double { double(self: Box<Self>) -> usize5 fn double(self: Box<Self>) -> usize; 6 } 7 8 impl double for usize { double(self: Box<usize>) -> usize9 fn double(self: Box<usize>) -> usize { *self * 2 } 10 } 11 main()12pub fn main() { 13 let x: Box<_> = Box::new(3); 14 assert_eq!(x.double(), 6); 15 } 16