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To: caml-list@inria.fr
Subject: Re: [Caml-list] initializers and destructor
References: <20020331210924.GA11224@cs.unibo.it>
From: Remi VANICAT <vanicat@labri.u-bordeaux.fr>
Date: 31 Mar 2002 23:41:23 +0200
In-Reply-To: <20020331210924.GA11224@cs.unibo.it>
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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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