As_ref().to_string() et al

help
1

I skimmed through a blog a while back that stated that if one is doing:

fn foo<S: AsRef<str>>(s: S) {
  // ...
  let bar = s.as_ref().to_string();
  // ...
}

(with .as_ref().to_string() being the operative part) then it's a sign one has not understood From and Into.

As it happens, I have a few of those, including .as_ref().to_path_buf() for AsRef<Path> bounds.

Unfortunately I have been unsuccessful in finding that blog post again, but I suspect it was directed at people like myself.

Could someone shed some light on what the issues is, and what one should be doing instead?

2

If you want to have an owned value anyway, <S: Into<String>> would express this more clearly. It also gets rid of an unnecessary clone if someone calls your method with a String.

2 Likes
3

The issue is that if someone calls it with S = String, then you will clone it even though there's no need to. The Into<String> trait would not result in a clone of the string.

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4

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