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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: ADA Popularity Discussion Request
Date: Wed, 15 Sep 2004 14:50:42 +0200
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Date: 2004-09-15T14:50:42+02:00
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On Wed, 15 Sep 2004 12:14:31 +0200, Martin Krischik wrote:

> Dmitry A. Kazakov wrote:
> 
>> Should it be generic, parametrized by a
>> string type. Which is BTW impossible too, because even at the level of
>> generics the least common ancestor of all Ada string types is "type Duno
>> is private";
> 
> I think you have not worked enough with generics.
> 
> generic
> 
>    type Character_Type is (<>);
> 
>    type String_Type is array (Positive range <>) of Character_Type;
> 
> package Some_Generic_String_Operations
>
> But there is a problem of course: Unbounded_String is not a generic
> instantiation. It really should have been:
> 
> package Unbounded_String
> is new Generic_Unbounded_String (
>    Character_Type => Character,
>    String_Type => String);
> 
> package Wide_Unbounded_String
> is new Generic_Unbounded_String (
>    Character_Type => Wide_Character,
>    String_Type => Wide_String);

They couldn't do it, because of ranges/slices/attributes. They are not
first class citizens, alas.

Then it could be:

generic -- This is not Ada!
   type Index_Type is (<>);
   type Index_Range_Type is range of Index_Type;
   type Element_Type is private;
   type Array_Type is
      array (Index_Type range Index_Range_Type)
         of Element_Type;
package Abstract_Array is ...

Anyway, an equivalent, but more straightforward way is just to make
Unbounded_String matching

   type String_Type is array (Positive range <>) of Character_Type;

Once, you solved the problem of wired slices and attributes, the rest will
be easy.

> And sadly it is to late for that.

Not at all. Solve the above and add supertypes. That will do the trick. You
create a common array ancestor *afterwards* and everybody is happy.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de