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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Type safety on wikipedia
Date: Fri, 27 Jan 2006 19:38:47 +0000
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Date: 2006-01-27T19:38:47+00:00
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"Alex R. Mosteo" <devnull@mailinator.com> writes:

> Simon Wright wrote:
>> "Alex R. Mosteo" <devnull@mailinator.com> writes:
>> 
>>>This is something I've mused about sometimes: Let's suppose some Ada
>>>compiler goes ahead and provides a GC. What happens with programs
>>>written without taking this into account?
>> 13.11.2(17) only says that Free _should_ reclaim the storage. I
>> suppose for a GC implementation there could be at least 2
>> implementation strategies:
>>  * don't actually reclaim, just remove local reference and deal with
>>    tasks if necessary
>>  * check that the reference count is in fact 1 and raise *_Error if
>>    not! That would be useful!
>
> Neat! I hadn't figured that path of action. Indeed it seems a very
> good strategy. I can imagine unknown bugs popping out after years of
> silently wait and rare crashes... hehe...

One point I had forgotten is that deallocation of a controlled object
will finalize it -- LRM 13.11.2(9) -- so looking at it through a
dangling pointer will be a Bad Thing even if GC has ensured that the
mamory hasn't been re-used for something else.