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Date: Thu, 16 Mar 2000 14:34:57 +0100
From: "thierry BRAVIER" <thierry.bravier@dassault-aviation.fr>
Organization: Dassault Aviation
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To: caml-list@inria.fr
Subject: Re: typing of a class
References: <38C50056.9A272C81@enseeiht.fr> <m38bt4n3n7u.fsf@pacherenc.inria.fr> <20000310093324.41034@pauillac.inria.fr>
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Dear ocamlers,

Xavier Leroy a =E9crit:

> You can write your example just like in Java, by 1- making the
> instance variable mutable, and 2- using an option type to play the
> role of Java's null pointers.  You'd get:
>
> class a arg =3D object(self)
>     val mutable ob =3D (None : b option)
>     initializer ob <- Some(arg self)
>   end;;
>
> It's not pretty, but that's exactly what's going on "under the hood"
> in the equivalent Java code.
>
> - Xavier Leroy

An alternative technique I often use is

let not_ready () =3D failwith "not ready"

class a arg  =3D object (self)
  val mutable ob =3D not_ready
  initializer let it =3D arg self in ob <- (fun () -> it)
  method private ob =3D ob ()
end

the advantage is that it is not necessary anymore to match ob with Some x=
;
the drawback is that 'ob' value must now be accessed as 'ob ()'.
A workaround is to introduce method ob and type 'self#ob'.

Of course, field ob must not be accessed during (arg self) computation :-=
(

Cheers.