#![feature(fn_traits)]
#![feature(unboxed_closures)]

struct Closure {
    a: u32,
    b: u32
}

impl FnOnce<(u32,)> for Closure {
    type Output = u32;

    extern "rust-call" fn call_once(self, (c, ): (u32, )) -> Self::Output {
        self.a + self.b + c
    }
}


fn main() {
    use std::mem;

    let a = 1;
    let b = 2;

    let with_lambda = move |c: u32| a + b + c;
    let with_struct = Closure { a, b };

    let lambda_size = mem::size_of_val(&with_lambda);
    let struct_size =mem::size_of_val(&with_struct);

    assert_eq!(lambda_size, struct_size);
    assert_eq!(lambda_size, mem::size_of_val(&a) + mem::size_of_val(&b));

    assert_eq!(with_lambda(3), 6);
    assert_eq!(with_struct(3), 6);
}