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From: Natasha Kerensikova <lithiumcat@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Reference counting and idempotent finalize
Date: Mon, 30 Sep 2013 06:25:15 +0000 (UTC)
Organization: A noiseless patient Spider
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Date: 2013-09-30T06:25:15+00:00
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Hello,

On 2013-09-11, Natasha Kerensikova <lithiumcat@gmail.com> wrote:
> I have recently reinvented the reference counted wheel, and been told
> that I got it all wrong because Finalize must be idempotent. However I
> already diffusely knew that, though I cannot remember from where it
> comes or whether I thought of it as a hard requirement or only as a good
> practice (the difference is hard to tell when such a rule is
> internalized).
>
> Anyway, my naive implementation looks like that:
>
>    [...]

So I have published the implementation on github (and on a public fossil
repository on my server, but that's nearly as trendy), it's available
at :
https://github.com/faelys/natools/blob/trunk/src/natools-references.ads

One feature it has that I haven't found it most other implementations
mentioned here or found through a web search, is that it places no
requirement on the referenced type.

In particular, it allows creating reference to any existing type without
having to change it, e.g. Ada.Text_IO.File_Type.

The fact that it supports referencing to a limited type is a large part
of my needs. I remember someone here (I think it was Randy) saying that
limited types are a pain and should be avoided in public interfaces, in
favor of a reference-semantic non-limited type. So I declare the
intrinsically limited type in the private part of the specification and
use the reference counter to provide the semantics of the public type.
That's why I haven't found the need yet for weak references or
concurrency.

Any comment about my code is welcome, should anyone take the time to
have a look at it.


Thanks for your help,
Natasha