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Comment by jstimpfle | Hacker News Reader

std::string is not UTF-8 and can't be made UTF-8. It's encoding agnostic, its API is in terms of bytes not codepoints.

Of course it can be made UTF-8. Just add a codepoints_size() method and other helpers.

But it isn't really needed anyway: I'm using it for UTF-8 (with helper functions for the 1% cases where I need codepoints) and it works fine. But starting with C++20 it's starting to get annoying because I have to reinterpret_cast to the useless u8 versions.

First, because of existing constraints like mutability though direct buffer access, a hypothetical codepoints_size() would require recomputation each time which would be prohibitively expensive, in particular because std::string is virtually unbounded.

Second, there is also no way to be able to guarantee that a string encodes valid UTF-8, it could just be whatever.

You can still just use std::string to store valid encoded UTF-8, you just have to be a little bit careful. And functions like codepoints_size() are pretty fringe -- unless you're not doing specialized Unicode transformations, it's more typical to just treat strings as opaque byte slices in a typical C++ application.

Perfect is the enemy of good. Or do you think the current mess is better?

std::string _cannot_ be made "always UTF-8". Is that really so contentious?

You can still use it to contain UTF-8 data. It is commonly done.

I never said always. Just add some new methods for which it has to be UTF-8. All current functions that need an encoding (e.g. text IO) also switch to UTF-8. Of course you could still save arbitrary binary data in it.

> That's where the standard should come in and say something like "starting with C++26 char is always 1 byte and signed. std::string is always UTF-8" Done, fixed unicode in C++.

> I never said always

Yes you totally did. And regarding "add some new methods for which it has to be UTF-8", there is no need at all to add UTF-8 methods to std::string. It would be a bad idea. UTF-8 is not bound to a particular type (or C++ type). It works on _any_ byte sequence.

You're right, sorry.

Good point, so maybe the standard should just add some functions that take std::string_view. Definitely not add a whole new class like std::u8string ...

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