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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: User-defined type attributes
Newsgroups: comp.lang.ada
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Date: Fri, 14 Mar 2008 10:00:46 +0100
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Date: 2008-03-14T10:00:46+01:00
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On Thu, 13 Mar 2008 20:46:41 -0500, Randy Brukardt wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
> news:965suhjl0bxt$.74se2ylyksin.dlg@40tude.net...
> ...
>> Why? The only thing you need is formal generic ADTs. Ada's generics lack
>> ADTs, which is the reason why you need to pass operations together with the
>> formal types. There exist formal built-in types like "private", "<>",
>> "digits <>" etc, but there is no user-defined ones. Add these and all
>> primitive operations will go with the actual type just per magic. It would
>> be IMO a natural step for anybody who wanted generics to evolve in an
>> Ada-way. (Not for me, as you know, I prefer generics removed from the
>> language.)
> 
> Generic formal derived types are the way to bring an ADT into a generic.
> After all, they do bring in all of the primitive operations of the ADT.
>
> The only problem is that they can't be used on unrelated types, but that's
> not very relevant if you are using tagged types (and you might as well being
> doing so if you're defining any sort of composite type).

Right, but this also implies that there is no need to have generics at all.
A class-wide object does all what needed:

   generic
      type S is new T with private;
   procedure Foo (X : in out S);

can be replaced by:

   procedure Foo (X : in out T'Class);

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