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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: Garbage Collection in Ada
Date: 1996/10/17
Message-ID: <dewar.845559504@merv>#1/1
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references: <01bbb910$f1e73f60$829d6482@joy.ericsson.se>
 <199610132138291604607@dialup101-6-14.swipnet.se> <dewar.845247229@merv>
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organization: New York University
newsgroups: comp.lang.ada
Date: 1996-10-17T00:00:00+00:00
List-Id: <comp.lang.ada>


HJB says

"It could require the existence of a collector, and a (partially)
conservative collector may well be the most viable implementation
strategy."

What would it mean to sanction the existence of a collector. As I noted
earlier, at most it could mean that you provide for the possibility of
unreachable blocks disappearing, but there are several problems here:


1. Since you only *allow* such collection, completely ignoring the requirement
is a valid semantic interpretation.

2. Since you can only collect unreachable blocks, the removal of them has
null semantics in any case, unless you allow finalization to happen at
unpredictable points, a nasty thought!

3. You cannot require blocks to disappear, since if you have conservative
collectors in mind they do not guarantee to free even a single block in
a given program.

Conservative collectors are a clever idea, and are a clever response to 
dealing with wanting GC in an implementation that does not otherwise
provide GC, but I don't see that the concept has any relevance in language
design.