struct Foo {
    n: u32,
}

impl Foo {
    fn bar(&mut self) {
        println!("{}", self.n)
    }
}

struct Caller<T> {
    data: T,
    f: fn(T),
}

fn main() {
    let mut foo = Foo { n: 100 };
    let c = Caller { data: &mut foo, f: Foo::bar, };
}