Objective-c Rust macros

Why does this exist? Who knows... but it lets you do cool stuff like this:

    let my_class = register_class!(MyClass:NSObject with {
        (pub width: u32),
        (priv height: u32),
        (sel add:(i32)t1 with:(i32)t2 -> i32 with |obj, sel| {
            return t1+t2;
        }),
    });
    
    let obj = unsafe { msg_send![msg_send![my_class, alloc], init] };
    let x: i32 = unsafe { msg_send![*obj, add:5 with:6] };
    assert_eq!(x, 11);