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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Limited use for limited with?
Date: Tue, 5 Oct 2010 02:35:46 -0500
Organization: Jacob Sparre Andersen
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Date: 2010-10-05T02:35:46-05:00
List-Id: <comp.lang.ada>

"Maciej Sobczak" <see.my.homepage@gmail.com> wrote in message 
news:f059316d-9994-4ea4-b984-f9530768bfbc@d25g2000yqc.googlegroups.com...
...
> Not at all. In my design Object knows nothing about registry. There is
> no such dependency and therefore it does not have to be broken.

But the Registries are completely unsafe! They have no way to protect 
against dangling pointers, so any client mistake (and clients make *lots* of 
mistakes) will cause the entire system to crash or malfunction. (And this 
will be the worst kind of crash, with no possible way to finding where it 
came from, since the crash will occur long after the actual error and not be 
tied to it in any way.)

It's always better to prevent abuse in the interface. And in this case, I 
don't think you have any choice unless you are willing to assume that your 
clients are perfect (ha!). Storing arbitrary general access values is no 
safer than storing a link to an object without finalization protection. You 
shouldn't do either one of them.

Unless you like to spend many hours in a debugger, single-stepping your 
code, you will find some way to protect the registries against the 
possibility of dangling pointers. And that is going to require some sort of 
cooperation (or deep copies, which I agree will often not work).

                              Randy.