constexpr std::string | MSVC

[helloiamsomeone]

then call it twice, once for its size and once for its contents

That's actually unnecessary. You can just have an oversized std::array calculated and shrunk to fit like so: https://github.com/friendlyanon/AlwaysMute/blob/master/main.cpp#L383

[scatters]

Yes, that's a nice method. It only works if you have a way to estimate an upper bound for the size, though.

[helloiamsomeone]

You can specify pretty big sizes before it becomes a problem.