I agree - Structs are kind of a nicer solution here. Especially because it’s pretty common to pass a whole set of options through the call stack.

In Python land you end up with functions with 30 arguments and when they want to pass them anywhere they give up and use kwargs which are completely awful and should almost never be used.

Remember that this has no runtime cost and is fully type-safe.

For the sake of maximal accuracy, enum size overhead can become relevant sometimes. But a work-around exists (boxing the huge variant), and with or without boxing, the performance would still beat whatever other languages have to offer.

Otherwise, good post (I would have to say that since it mostly rehashes points I made in previous comments 😉).

This one:

fn resize(width: u32, height: u32) {}
fn offset(dx: u32, dy: u32) {}

let f: fn(u32, u32) = if resizing { resize } else { offset };

gets rewritten to something non-equivalent:

struct Size {
    width: u32,
    height: u32,
}

fn resize(size: Size) {}

// No more arguing about arguments
let f: fn(Size) = resize;

But I would say that the original idea of applying wildly different functions depending on a flag shouldn’t be easily achievable, because it’s a bad idea a lot of times.