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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: newbie Q: storage management
Date: 1997/05/06
Message-ID: <dewar.862915787@merv>#1/1
X-Deja-AN: 239718790
References: <5k5hif$7r5@bcrkh13.bnr.ca> <336754A0.41C6@magellan.bgm.link.com>
 <JSA.97Apr30181307@alexandria> <336A065B.41C6@magellan.bgm.link.com>
 <dewar.862662935@merv> <336E15A4.167E@magellan.bgm.link.com>
Organization: New York University
Newsgroups: comp.lang.ada
Date: 1997-05-06T00:00:00+00:00
List-Id: <comp.lang.ada>


Sam said

<<The only thing I don't understand about this posting is why you think
it contradicts mine.  The technical argument is that there is no
consensus on whether GC is needed or what kind should be specified.  GC
advocates don't agree with that, but were unable to convince everyone
else during the revision process.  The best approach now for GC advocates
would be to do one or more straw-man implementations.>>


Actually it is not true that "GC advocates don't agree with that". There
is definitely no consensus among GC advocates as to what a GC annex
might look like. Opinions range from "no annex is needed, because nothing
needs to be said in the RM -- this is an implementation issue, not 
something subject to formal specification" to "we need lots of interfaces
for user control over the GC stuff".

I would not talk about straw-man implementations, I would talk about
real usable implementations. It is much more important that something
be real and usable, than it is that it be in the standard. If someone
did a nice GC implementation for GNAT, and people started using it,
then a lot of the problem is solved. True, not all Ada 95 compilers
would have the feature but

(a) There are lots of useful things that one Ada implementation has that
another does not have that lead one to choose one implementation over
another. For example, if you are using Ada 95 on NT, and you want a
GUI builder to come with it, you may well choose Aonix. If you need the
information systems annex, you may well choose GNAT. The latter example,
the special needs annex, is particularly appropriate, since at best you
could get an SN annex for GC, and that would not in any case guarantee
that it would be on all compilers.

(b) If GC was really useful, then other vendors would be encouraged to do it.

The thing to remember here is that the major function of the special needs
annexes is to ensure that if there is a feature that will be implemented
by multiple vendors, then it should be implemented identically.

In other words, the really strong argument for a GC annex would be if
you now saw a situation in which lots of Ada 95 vendors were rushing to
implement GC in an incompatible manner. I don't see that happening yet :-)