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To: David Chemouil <David.Chemouil@enseeiht.fr>
Cc: caml-list@inria.fr
Subject: Re: typing of a class
References: <38C50056.9A272C81@enseeiht.fr>
From: John Prevost <prevost@maya.com>
Date: 08 Mar 2000 14:00:29 -0500
In-Reply-To: David Chemouil's message of "Tue, 07 Mar 2000 14:12:54 +0100"
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David Chemouil <David.Chemouil@enseeiht.fr> writes:

> I've been using the OO features of Caml these past days, and soon
> observed a behavior of the typing system that I don't understand. Here
> is a simplified version of my problem:
> 
> # class a (arg : a -> b) = object(self)
>     val ob = arg self
>   end
>   and b = object
>   end;;
> 
> The instance variable self
> cannot be accessed from the definition of another instance variable

> I don't understand why it is forbidden for an object to pass itself to
> another one (which is possible in Java or Eiffel for example). Could
> someone explain me? Or is there a paper talking about this?

The problem is that you're using self during the initialization of the
object, not in a method of the object.  Since the object isn't yet
initialized, it can't be passed to functions.  If you use a method,
you're okay:

class a (arg : a -> b) =
  object (self)
    method ob = arg self
  end
and b =
  object
  end

John.