Unicode advise not doing that at all
http://www.unicode.org/faq/private_use.html#pua10

And the properties are immutable across the universe for a given version of
Unicode. Algorithms etc depend on that
P1628 supports versioning but i guess that might not last

On Thu, 29 Aug 2019 at 13:05, Lyberta <lyberta_at_[hidden]> wrote:

> I wanted to tinker with Private Use Area code points and I thought what
> would be the standard way to do that. And it is obvious that we need a
> UCD class and use it to hold the user-defined properties of Private Use
> Area code points.
>
> This is completely opposite of P1628.
>
> We define a new class std::unicode::character_database (established
> name, although I'd prefer calling it std::unicode::code_point_database)
> and similarly to std::source_location it has static function default()
> that will return the reference to const default UCD. Obviously, the
> entire class should be constexpr.
>
> Now, my initial idea was to make only Private Use Area mutable while the
> rest is const but then it occurred to me that it will deny some nice
> possibilities such as 3rd party libraries shipping older and newer
> versions of UCD that is shipped with the standard library.
>
> Essentially, I think the entire database should be mutable.
> std::unicode::character_database should be a value type but I guess we
> may word it so it is possible to implement mutations from default as a
> separate internal state while the rest of the database simply links to
> default one, like copy-on-write.
>
> I don't have the API or the wording yet. This is just thoughts at this
> point but it seems like P1628 is not the way to go at all.
>
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