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From: "James A. Squire" <m193884@CSEHP3.MDC.COM>
Subject: type casting tagged types in the wrong direction
Date: 1996/03/27
Message-ID: <3159B860.28A6@csehp3.mdc.com>#1/1
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sender: Ada programming language <INFO-ADA@VM1.NoDak.EDU>
comments: cc: ja_squire@csehp3.mdc.com
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organization: MDA Avionics Tools & Processes
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Date: 1996-03-27T00:00:00+00:00
List-Id: <comp.lang.ada>

I have a question:

Say I have something like:

type A is tagged
  record
    X : ABC;
    Y : DEF;
  end record;

type B is new A with
  record
    W : GHI;
  end record;

type C is new B with
  record
    Z : JKL;
  end record;


OK.  Now, let's say that I forgot which type extends off of which, and I
write a statement like this:

  Jim  : C;
  Jane : B;
  Save : JKL;

begin
  ...
  Jim := C (Jane);
  Save := Jim.Z;
  ...
end;

GNAT 3.03 compiles this statement.  Is that really right?  Is Jim.Z
defined?
According to the LRM 4.6, the above is called a "view conversion".  This
raises the question, how do you take a type C view of a type B entity
when type C looks for additional information?

Should a validated Ada95 compiler flag this usage?  I realize that GNAT
is not validated.

I would appreciate any expert or otherwise opinions that any of you have
to offer.
Thank you.
--
James Squire
MDA Avionics Tools & Processes
ja_squire@csehp3.mdc.com
"one of these days I'm going to better myself by going to Knight school"