#![feature(fn_traits, unboxed_closures)] use std::ops::FnMut; struct S { x: isize, y: isize, } impl FnMut for S { //~^ ERROR type parameter to bare `FnMut` trait must be a tuple extern "rust-call" fn call_mut(&mut self, z: isize) -> isize { //~^ ERROR functions with the "rust-call" ABI must take a single non-self tuple argument self.x + self.y + z } } impl FnOnce for S { //~^ ERROR type parameter to bare `FnOnce` trait must be a tuple type Output = isize; extern "rust-call" fn call_once(mut self, z: isize) -> isize { //~^ ERROR functions with the "rust-call" ABI must take a single non-self tuple argument self.call_mut(z) } } fn main() { let mut s = S { x: 1, y: 2 }; drop(s(3)) }