//@ aux-build:go_trait.rs extern crate go_trait; use go_trait::{Go,GoMut}; use std::fmt::Debug; use std::default::Default; struct MyThingy; impl Go for MyThingy { fn go(&self, arg: isize) { } } impl GoMut for MyThingy { //~^ ERROR E0119 fn go_mut(&mut self, arg: isize) { } } fn main() { }