Re: Ada and Unicode

["Randy Brukardt" <randy@rrsoftware.com>]

"Luke A. Guest" <laguest@archeia.com> wrote in message 
news:s5jute$1s08$1@gioia.aioe.org...
>
>
> On 19/04/2021 13:52, Dmitry A. Kazakov wrote:
>
> > It is practical solution. Ada type system cannot express differently
> represented/constrained string/array/vector subtypes. Ignoring Latin-1 and 
> using String as if it were an array of octets is the best available 
> solution.
> >
>
> They're different types and should be incompatible, because, well, they 
> are. What does Ada have that allows for this that other languages doesn't? 
> Oh yeah! Types!

If they're incompatible, you need an automatic way to convert between 
representations, since these are all views of the same thing (an abstract 
string type). You really don't want 35 versions of Open each taking a 
different string type.

It's the fact that Ada can't do this that makes Unbounded_Strings unusable 
(well, barely usable). Ada 202x fixes the literal problem at least, but we'd 
have to completely abandon Unbounded_Strings and use a different library 
design in order for for it to allow literals. And if you're going to do 
that, you might as well do something about UTF-8 as well -- but now you're 
going to need even more conversions. Yuck.

I think the only true solution here would be based on a proper abstract 
Root_String type. But that wouldn't work in Ada, since it would be 
incompatible with all of the existing code out there. Probably would have to 
wait for a follow-on language.

                 Randy.