1 #![feature(unboxed_closures)] 2 to_fn_mut<A,F:FnMut<A>>(f: F) -> F3 fn to_fn_mut<A,F:FnMut<A>>(f: F) -> F { f } 4 main()5 fn main() { 6 let mut_ = to_fn_mut(|x| x); 7 mut_.call((0, )); //~ ERROR no method named `call` found 8 } 9