From: MikkelFJ <mikkelfj-anti-spam@...>
Date: 2003-05-20T11:49:55+09:00
Subject: Re: An Object Going Out Of Scope


"Brian Candler" <B.Candler@pobox.com> wrote in message
news:20030519161809.GA2900@uk.tiscali.com...
> On Tue, May 20, 2003 at 12:55:22AM +0900, MikkelFJ wrote:
> > I didn't go through all you examples, but I did say that you could still
> > have references at time of finalization.
>
> But then what is the purpose of a "finalizer"?
>
> It's possible for an object to be assigned to a variable which goes out of
> scope lots of times!

The fact that you can close a file handle many times does not lead the
conclusion that files should not be closed.
I'm interested in ensuring cleanup after the scope of interest terminates,
not the scope or lifetime of a variable or object as this can be arbitrarily
complex. Just because we have GC  we don't have to give up on stack
semantics.

> Would you really want to call a finalizer 6 times on the same object in
the
> above example? I don't think so.

I would write my code in a sensible way. Making things easier does not
liberate you from the necessity of reflecting about what you are doing. You
seem to be assuming any object should be automatically finalized every time
a reference goes out scope. This is not the point. Apart from that, you
sometimes do want to call a cleanup method many times. Reference counted
resources and semphores comes to mind. critsec.enter, critsec.exit. I recall
a thread where some posters did have a problem with controlling file life
time where I proposed a simple refcounted solution.

> I think you are proposing that the variable itself can be tagged in a
> special way, "do X when this variable goes out of scope". But you can
> achieve this using 'ensure' already, without having to get the interpreter
> involved:

True, except it is more the auto declaration that goes out of scope, not
necessarily the variable.
I realized the ensure equivalance myself. See other post.
With the auto syntax, you could programmatically do some more advanced
cleanup logic which ensure would only make possible using preprocessed
defines. Maurico was hinting at some almost possible implementation.
In any case, ensure is a great feature that solves the essential problem.

>
> > { auto(:$critsec, :exit); @critsec.enter; .... }
>
> That doesn't make any sense to me - a global variable can never go out of
> scope?

No, but the auto declaration does. It's just like ensure at the end. I think
you do follow me according to what you wrote earlier

Mikkel