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From: dewar@cs.nyu.edu (Robert Dewar)
Subject: Re: A note on GNAT 3.05 performance
Date: 1996/06/24
Message-ID: <dewar.835605407@schonberg>#1/1
X-Deja-AN: 162474460
references: <dewar.835245019@schonberg> <4qeubm$8th@linus.mitre.org>
 <DtF35x.5D@jvdsys.nextjk.stuyts.nl>
organization: Courant Institute of Mathematical Sciences
newsgroups: comp.lang.ada
Date: 1996-06-24T00:00:00+00:00
List-Id: <comp.lang.ada>

"Michael F Brenner (mfb@mbunix.mitre.org) wrote:

: Is this why djgpp DOS interrupts don't work any more...because
: the structure containing the registers is a record type?
"

The best guess is that this relates to code that improperly assumes
that records are passed by reference. In Ada (and in GNAT) whether
a record is passed by reference or copy is implementatoin dependent
and may change from one version of the compiler to another, or
from one port to another (for example, in some ports, small records
are passed by value in registers).

If you want something passed by reference and your code depends on it,
either use an access parameter (if the value is guaranteed to be non-null)
or an explicit access type. This is the only legitimate way to be sure
that a record is passed by reference.