Rust

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.