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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: System.Address_to_Access_Conversions
Date: 1998/07/26
Message-ID: <dewar.901492897@merv>#1/1
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nabassi said

<<there is a paper on www.gnat.com called "Ada 9x tagged types and their
implementation in GNAT".  by Crille COmer and Brett Porter. it says:

"for many reasons, it turns out to be mandotary that any field in a tagged
type keep the same location within the record in the any descendant type",

then later on they say .."this compoenent is inserted at the top of the
record forcing the additional compoenents at the end"..

and they show a digram showing the tag field at the top of the record as
a pointer to dispatch table.
>>


Just because one particular versoin of GNAT made this choice, does not
mean that other compilers wlil make the same choice, or even future
versions of GNAT. The paper you refer to is a discussion of the implementation
techniques planned for GNAT 7 years ago. It is not even accurate with respect
to the current GNAT implementation, let alone being a necessarily accurate
description of what other Ada 95 compilers nmight do!