#![feature(box_syntax)]
#![feature(trait_alias)]
#![feature(unboxed_closures)]

fn c<T: FnMutClone<()>>(x: T) {}

trait FnClone<Args>: Fn<Args> {
    fn clone_fn(&self) -> Box<dyn FnClone<Args, Output = Self::Output>>;
}
impl<Args, T: Fn<Args> + Clone + 'static> FnClone<Args> for T {
    fn clone_fn(&self) -> Box<dyn FnClone<Args, Output = Self::Output>> { Box::new(self.clone()) }
}

trait FnMutClone<Args>: FnMut<Args> {
    fn clone_fn(&self) -> Box<dyn FnMutClone<Args, Output = Self::Output>>;
}
impl<Args, T: FnMut<Args> + Clone + 'static> FnMutClone<Args> for T {
    fn clone_fn(&self) -> Box<dyn FnMutClone<Args, Output = Self::Output>> { Box::new(self.clone()) }
}

fn a() -> Box<dyn FnMutClone() -> ()> {
    let a = 1;
    box move || { a += 1; }
}

fn main() {
    c(a())
}