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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: To collection (GNAT bug)
Newsgroups: comp.lang.ada
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Date: Wed, 4 Oct 2006 14:10:57 +0200
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Date: 2006-10-04T14:10:57+02:00
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On Wed, 04 Oct 2006 11:27:15 +0200, Georg Bauhaus wrote:

> If you would like to have user level internal data structure
> representation interfaces for arrays, pointers, etc.,

No, I don't like to care about them. This is exactly why the
language/compiler provided conversions must be reasonable, or else illegal.
Ada is not C.

> how do you envision a suitably modified Ada compiler to guarantee
> separate compilation, optimization, and LRM-correct
> behavior in the presence of user-defined internal representations?

You should ask this question yourself. In particular, consider the code I
sent once:

   package Legal is new Address_To_Access_Conversions (String);
   function To_Addr (X : Ptr) return Address is
   begin
      return Legal.To_Address (X.all'Unchecked_Access);
   end To_Addr; -- This is safe

   function To_Ptr (X : Address) return Ptr is
      function Cast is
         new Ada.Unchecked_Conversion (Legal.Object_Pointer, Ptr);
   begin
      return Cast (Legal.To_Pointer (X));
   end To_Ptr;

What is user-defined in To_Ptr (To_Addr (X))?

----------------------
Clearly a lack of safe general to pool specific conversion of access types
is a language design fault. So? Should the compiler vendors make it even
worse, by making Unchecked_Conversion return rubbish when the programmer
resort to it?

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