trait T {
    fn f(&self);
}

#[allow(dead_code)]
struct A {
    i: i32
}

impl T for A {
    fn f(&self) {}
}

fn f<T : ?Sized>(_: &T) {}
//fn g<T : ?Sized>(_: T) {} Error

trait T2 {
    fn foo(&self) -> Box<T2>;
    fn bar() -> Box<T2> where Self : Sized;
}

impl T2 for A {
    fn foo(&self) -> Box<T2> {
        println!("foo");
        Box::new(A{ i: 5 })
    }

    fn bar() -> Box<T2> {
        println!("bar");
        Box::new(A{ i: 5 })
    }
}

trait T3 {} // : Sized {}

impl T3 for A {}

fn main() {
    let a = A{ i: 5 };
    let _t : &T = &a;
    f::<T>(&a);

    let _b : Box<T2> = T2::foo(&a);
    let _c : Box<T2> = <A as T2>::bar();

    let _d : &T3 = &A{i: 5};
}