#![feature(fn_traits, unboxed_closures)] use std::ops::FnMut; struct S { x: isize, y: isize, } impl FnMut for S { extern "rust-call" fn call_mut(&mut self, z: isize) -> isize { self.x + self.y + z } //~^^^ ERROR functions with the "rust-call" ABI must take a single non-self argument } impl FnOnce for S { type Output = isize; extern "rust-call" fn call_once(mut self, z: isize) -> isize { self.call_mut(z) } //~^ ERROR functions with the "rust-call" ABI must take a single non-self argument } fn main() { let mut s = S { x: 1, y: 2, }; drop(s(3)) //~ ERROR cannot use call notation }