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From: kaz@vision.crest.nt.com (Kaz Kylheku)
Subject: Re: newbie Q: storage management
Date: 1997/05/04
Message-ID: <5kgtf1$js1@bcrkh13.bnr.ca>#1/1
X-Deja-AN: 239212188
References: <5k5hif$7r5@bcrkh13.bnr.ca> <JSA.97Apr30173548@alexandria>
 <dewar.862625257@merv>
Organization: Prism Systems Inc.
Newsgroups: comp.lang.ada
Date: 1997-05-04T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <dewar.862625257@merv>, Robert Dewar <dewar@merv.cs.nyu.edu> wrote:
>Jon answers Kaz:
>
><<> I know that it is possible to instantiate a generic freeing function
>> for explicitly destroying objects. But why is there is this lack of
>> symmetry in the language?
>
>Basically, this asymmetry is there because the designers did not think
>they could "require" GC (at least at the level of the high expectation
>of it for things like Lisp, Eiffel, ST, etc.) because many of the
>target areas of use would not need (or even require _not_ having) GC.
>But, the designers (especially Ada83) really were GC adherents, so
>they compromised and suggested that GC would be a very good thing for
>implementations to provide, but had to leave the door open for
>impls. only supplying manual deallocation.>>>
>
>
>Jon, I don't think this is the right answer, you are focussing too much
>on GC, but the question was not about GC, it was about the asymmetry
>(i.e. new is a straight forward primitive, free rquires a messy
>instantiation).
>
>In fact the assymetry is quite deliberate, and reflects the fact that
>new is safe (cannot result in erroneous execution), but free is dangerous
>(and can easily result in erroneous execution if misused).

Yes, that's all I really wanted to know, and I suspected as much.

It's perfectly clear that since a conforming Ada implementation is not required
to supply GC, a maximally portable Ada program cannot rely on its presence. It
would be foolhardy to write a program that expects the implementation to locate
unreachable objects and reclaim them, when the language doesn't require the
facility.