[Caml-list] initializers and destructor

[Caml-list] initializers and destructor

[Stefano Zacchiroli]

Hi all,
  I know and frequently use "initializer" construct in classes, but I'm
not able to find something like destructor that works exectly like an
initializer but that is invoked just before an object last reference is
lost.

Is this somewhat difficult to implement in relation with the OCaml GC or
I'm simply missing something?

TIA,
Cheers.

-- 
Stefano Zacchiroli - undergraduate student of CS @ Univ. Bologna, Italy
zack@cs.unibo.it | ICQ# 33538863 | http://www.cs.unibo.it/~zacchiro
"I know you believe you understood what you think I said, but I am not
sure you realize that what you heard is not what I meant!" -- G.Romney
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Re: [Caml-list] initializers and destructor

[Remi VANICAT]

Stefano Zacchiroli <zack@cs.unibo.it> writes:

> Hi all,
>   I know and frequently use "initializer" construct in classes, but I'm
> not able to find something like destructor that works exectly like an
> initializer but that is invoked just before an object last reference is
> lost.
> 
> Is this somewhat difficult to implement in relation with the OCaml GC or
> I'm simply missing something?

there is the finalise function in the module Gc of the standard
library. 

one can write a destructor using it :
# class foo =
    let f x = print_string "test"; print_newline () in
  object(s)
    initializer
      Gc.finalise f s
  end;;
class foo : object  end
# new foo;;
- : foo = <obj>
# Gc.full_major ();;
test
- : unit = ()
# 

but you should know that there is some pitfall with finalise :

# class foo =
  object(s)
    val bar = "test"
    initializer
      Gc.finalise (fun x -> print_string bar; print_newline ()) s
  end;;
class foo : object  end
# new foo;;
- : foo = <obj>
# Gc.full_major ();;
- : unit = ()
# Gc.full_major ();;
- : unit = ()

here, the created object is reachable from the closure of
finalisation, so it's reachable, and never garbage collected.

You should carefully read it's documentation

-- 
Rémi Vanicat
vanicat@labri.u-bordeaux.fr
http://dept-info.labri.u-bordeaux.fr/~vanicat
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Re: [Caml-list] initializers and destructor

[Stefano Zacchiroli]

On Sun, Mar 31, 2002 at 11:41:23PM +0200, Remi VANICAT wrote:
> there is the finalise function in the module Gc of the standard
> library. 

Thanks, this is ok for me.

Anyway you probably agree with me that this kind of destructor are a bit
tricky: what about adding some syntactic sugar to hide the Gc usage to
who wants to use destructors? In that way we can also avoid the problem
of wrong usage of "finalise" using let binding correctly.

What do you think about it?

Cheers,
Thanks again.

-- 
Stefano Zacchiroli - undergraduate student of CS @ Univ. Bologna, Italy
zack@cs.unibo.it | ICQ# 33538863 | http://www.cs.unibo.it/~zacchiro
"I know you believe you understood what you think I said, but I am not
sure you realize that what you heard is not what I meant!" -- G.Romney
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To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
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Re: [Caml-list] initializers and destructor

[Remi VANICAT]

Stefano Zacchiroli <zack@cs.unibo.it> writes:

> On Sun, Mar 31, 2002 at 11:41:23PM +0200, Remi VANICAT wrote:
> > there is the finalise function in the module Gc of the standard
> > library. 
> 
> Thanks, this is ok for me.
> 
> Anyway you probably agree with me that this kind of destructor are a bit
> tricky: what about adding some syntactic sugar to hide the Gc usage to
> who wants to use destructors? In that way we can also avoid the problem
> of wrong usage of "finalise" using let binding correctly.
> 
> What do you think about it?

In fact, it should be more than syntactic sugar, because of the
pitfall of finalise. So may be it would be useful, but there is a lot
of work for it.

-- 
Rémi Vanicat
vanicat@labri.u-bordeaux.fr
http://dept-info.labri.u-bordeaux.fr/~vanicat
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