The general usability impact matters slightly less than it looks here, in part because the `do_math` with references in the article has two extra &s, and in par

The general usability impact matters slightly less than it looks here, in part because the `do_math` with references in the article has two extra &s, and in part because methods autoreference when called like x.f(). Performance-wise, if you're likely to touch every element in a type anyway, err on the side of copies. They are going to have to end up in registers eventually anyway, so you might as well let the caller find out the best way to put them there.