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From: Dmitry A.Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: RE: runtine instanciation
Date: Wed, 19 Jun 2002 00:35:09 +0200
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Date: 2002-06-19T00:35:09+02:00
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Robert C. Leif wrote:

> From: Bob Leif
> To: Dmitry Kazakov et al.
> 1) I do not believe that sacrificing the reliability of the entire
> program by switching to SmallTalk is a reasonable solution.

It was just a joke, sorry. (:-))

> 2) Even if I create a tagged type for my record, I still have to fill
> its fields. As I previously stated, the allowable data types and their
> methods have been previously compiled. I realize that one could use
> access types. However, I am hoping for a very simple static solution
> based on the use of the compiler. I believe that this is now well within
> the capabilities of the combination of modern Ada compilers and our PCs,
> which now have capabilities well beyond those envisaged by the original
> creators and users of Ada. I ran RR on an 8088 based 4.88 megahertz PC
> with I believe 256 K of RAM. I now, in order to run COTs products, have
> a computer with half a Gig of RAM and a 1.6 Gigahertz CPU. The bus width
> has now been expanded from 1 to 4 or 8 bytes. I suspect that the linker
> technology is the part that may have to be modified.

In your example types are known, so at least theoretically there is no need 
to do anything dynamically. Robert Eacus showed that in his post.

But if you really-really want full sized dynamic instantiations etc, you 
must in the first place allow things like:

type X is tagged ...;
procedure Foo (A : X);
...
declare
   type Y is new X with ...; -- New derived type
   procedure Foo (A : Y) is ... -- Overrides X's Foo
begin
   ...
end;
-- All side effects gone

It is not easy to do. You must dynamically modify dispatch tables and other 
internal structures (Ada.Tags.Internal_Tag). There would be utterly nasty 
things:

type X is tagged ...;
type X_Ptr is access all X'Class;
procedure Foo (A : X);
...
declare
   Nasty : X_Ptr;
begin
   declare
      type Y is new X with ...;
      procedure Foo (A : Y) is ...
   begin
      Nasty := new Y;
   end;
   Foo (Nasty.all); -- Oops!
end;

I'd liked to have that, but how to avoid all possible pitfalls?

-- 
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de