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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: How to get Ada to ?cross the chasm??
Date: Mon, 7 May 2018 18:54:24 -0500
Organization: JSA Research & Innovation
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Xref: reader02.eternal-september.org comp.lang.ada:52078
Date: 2018-05-07T18:54:24-05:00
List-Id: <comp.lang.ada>

"Paul Rubin" <no.email@nospam.invalid> wrote in message 
news:87po27fbv9.fsf@nightsong.com...
...
> I'd add as well: most refcount systems I know of don't move objects
> around in memory, so you get memory fragmentation and high cache miss
> rates.  GC systems typically compact the heap when the GC runs, ...

That would be extreme hard to do with Ada, since you'd have to avoid moving 
anything that is "pinned" by a representation clause, anything that uses 
'Address (unless you are prepared to follow that into all possible places), 
and anything imported/exported. You'd also have to be prepared to adjust 
'Access/'Unchecked_Access of aliased components. Sounds like a nightmare.

Similarly, figuring out what is reachable sounds like a nightmare, with 
local access objects of various kinds, access objects that point to stack 
objects, access values that come from foreign languages (i.e. C), and 
various tasking issues.

And of course the finalization issue mentioned before.

One could probably implement GC that worked for some subset of objects, but 
for the full language that seems both difficult and worthless (the latter 
because finalizing early is not allowed, so you could really only collect 
objects with trivial finalization).

                                           Randy.