> If you'd used `slices.Contains(s, needle)`, on the other hand, it could have such a performance bug in it and you'd never know.

Perhaps you're much better at programming than I am, but I prefer these semantics in a language because I figure they're much more likely to have been optimized empirically, support vectorization, and be less buggy than another rote loop I'm trying to speed through.

You're right. Just for information, slices.Contains() uses the index, not a copied value.

https://cs.opensource.google/go/go/+/refs/tags/go1.26.5:src/...

or contains() could be written by those who can write performant code, ..once

> on the other hand, it could have such a performance bug in it and you'd never know.

wut...? the debate isn't between closed (incompetent) source and open (competent) source - the debate is between verbose language and expressive language.