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Date: Wed, 2 Jul 2003 18:43:56 +0200
From: Nick Name <nick.name@inwind.it>
To: Mirko Aigner <Mirko.Aigner@alcatel.de>, caml-list@inria.fr
Subject: Re: [Caml-list] prevent more than one object
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On Wed, 02 Jul 2003 18:14:23 +0200
Mirko Aigner <Mirko.Aigner@alcatel.de> wrote:

> 
>  The problem is the class is still public and instances can be build,
>  any way to prevent this ?!

I would make the class private in the module and supply only access
functions; if you need it to be a class you should expose only the class
type, but there is Oo.copy so your value will never be granted unique.

Try this

module M : sig
  class type singleton = object
    method f : int
  end

  val x : singleton
end = 
struct
  class singleton = object
    method f = 0
  end

  let x = new singleton
end

You can't create a new singleton with "new" but still can do that with
Oo.copy M.x. It is better to completely hide the type if you can, as in

module M : sig
  type singleton

  val x : singleton
end = struct ...

Vincenzo

-- 
Ho dato al mio dolore la forma di parole abusate
che mi prometto di non pronunciare mai pił
[CSI]

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