I disagree. I think it should be indexed by bytes. One reason is what the other comment explains about not being constant-time (which is a significant reason), although the other is that this restricts it to Unicode (which has its own problems) and to specific versions of Unicode, and can potentially cause problems when using a different version of Unicode. A separate library can be used to deal with code points and/or EGC if this is important for a specific application; these features should not be inherent to the string type.

In practice, that is tiring as hell, verbose, awkward, unintuitive, requiring types attached to a specific instance for characters to do numeric indexing anyway and a whole bunch of other unnecessary ceremony not required in other languages.

We don't care that it takes longer, we all know that, we still need to do a bunch of string operations anyway, and it's way worse with swift than to do an equivalent thing than it is than pretty much any other language.

I don't think you can separate String from Unicode - that's what a "String" is in Swift.