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From: dewar@cs.nyu.edu (Robert Dewar)
Subject: Re: Free'ing extended types
Date: 1996/04/29
Message-ID: <dewar.830827168@schonberg>#1/1
X-Deja-AN: 152201415
references: <3183AC75.335C@ehs.ericsson.se> <DqMH63.Jvw@world.std.com>
 <3184D196.310B@ehs.ericsson.se> <4xpw8qvlau.fsf@lagrange.enst-bretagne.fr>
 <Dqn8u5.E3x@world.std.com>
organization: Courant Institute of Mathematical Sciences
newsgroups: comp.lang.ada
Date: 1996-04-29T00:00:00+00:00
List-Id: <comp.lang.ada>


Bob Duff said

"No, I don't think so.  The RM says an Unchecked_Deallocated object is
non-existent, and deallocating it is erroneous.  If you have a GC that
thinks it still exists, that's fine, but it's irrelevant to the formal
definition of erroneous.  (In this case I'd like the gc to raise an
exception, but of course that's not required, since erroneous means
*anything* can happen, including keeping the officially deallocated
object around and using it as usual.)"

Exactly! The definition of what is erroneous and what is not is a function
of the semantics of the language (in some cases, as has been pointed out
it is non-deterministic whether or not the execution is erroneous, since
it depends on implementation choices). But GC does NOT alter the semantics
of unchecked deallocatoin at all, and so is irrelevant to the consideration
of whether or not a program using unchecked deallocation is or is not
erroneous