Re: Why no Ada.Wide_Directories?

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

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"Pascal Obry" <pascal@obry.net> wrote in message 
news:4E9D87EB.6040203@obry.net...
...
>> Now, if an implementation on Windows doesn't have a way to use UTF-8
>> encoding, that is an implementation problem, but not one that the 
>> Standard
>> can do much about.
>
> But I can tell you that supporting UTF-8 on Windows is not trivial at all 
> as there is encoding/decoding needed in many places. Doing that is not 
> trivial and we had the need to invent the "encoding=[UTF8|8BITS]" mode for 
> Text_IO.Open for example.

I would not claim that it is easy. I haven't done anything about it for 
Janus/Ada, for example. (This falls into the "no one has complained, so 
other things have priority" category).

> As you say, implementation details, but can be easily defeated:
>
> If in my file I have:
>
>    Filename : constant String := "�t�";
>
> And this file is saved using UTF-8 encoding, then:
>
>    Text_IO.Open (Filename, ..., Mode => "encoding=8bits");
>
> Will just fail. A programmer error? Ok...

Right. That's the problem with the weak-typing that we've adopted for UTF-8 
and other encodings. It really has nothing to do with Open, it's a general 
problem with Ada..

The obvious solution (if this is a real problem in practice) would be to 
layer a strongly-typed layer on top of the existing facilities. Easy enough 
to do, but probably not something that will be in the Standard.

> Now:
>
>    Text_IO.Get (Filename, Last);
>    Text_IO.Open (Filename, ..., Mode => "encoding=8bits");
>
> What if the console is UTF-8?

If you're expecting to get Wide_Wide_Characters, you really ought to read a 
Wide_Wide_Character string. But I'm well aware that this solution is 
sub-optimal (especially in that it wastes huge amounts of space).

Short of completely abandoning the existing I/O system (not the worst idea, 
IMHO, but unlikely), I don't think there is any practical way to "fix" Ada 
to deal easily with the *rare* possibility of non-Latin-1 characters. If I 
was doing this from scratch, I would simply decree that all I/O strings are 
represented in UTF-8, and use a dedicated type for them so that they can't 
be mixed with "String" or "Wide_String".

                         Randy.