gistfile1.rs

macro_rules! offset_of(
    ($typename:ident, $fieldname:ident) => (
        unsafe {
            let ptr = std::ptr::null::<$typename>();
            std::ptr::to_unsafe_ptr(&(*ptr).$fieldname).to_uint() -
                ptr.to_uint()
        }
    );
)

#[test]
fn test_offset_of() {
    struct Foo {
        a: i32,
        b: u8,
        c: u16,
    };

    assert_eq!(offset_of!(Foo, a), 0);
    assert_eq!(offset_of!(Foo, b), 4);
    assert_eq!(offset_of!(Foo, c), 6);
}