trait MyFn<T> {
    fn call(self: Box<Self>, arg: &mut T);
}

impl<T, F: FnOnce(&mut T)> MyFn<T> for F {
    fn call(self: Box<Self>, arg: &mut T) {
        let this: Self = *self;
        this(arg)
    }
}

fn main() {
    let f: Box<MyFn<i32>> = Box::new(|arg: &mut i32| {
        println!("Argument: {}", arg);
    });
    let mut i = 10;
    f.call(&mut i);
}