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Message-ID: <363D7C18.FE3FB555@univ-savoie.fr>
Date: Mon, 02 Nov 1998 10:32:08 +0100
From: Christophe Raffalli <Christophe.Raffalli@univ-savoie.fr>
Organization: =?iso-8859-1?Q?Université?= de Savoie
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To: caml-list@inria.fr
Subject: Sharing inheritance ?
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I have a problem with the following situation:

---
class a (x : int) =
  object
    val mutable v = x 
    method get = v
    method set x = v <- x
  end 
;;
class b x =
  object (self)
    inherit a x as super
    method getb = self#get
    method setb = self#set
    method oldget = super#get
  end
;;
class c x =
  object (self)
    inherit a x
    method getc = self#get
    method setc = self#set
  end
;;
class d x = 
  object
    inherit b x
    inherit c x
  end
;;
(* produces:
Warning: the following methods are overriden by the inherited class:
  get set
Warning: this definition of an instance variable v hides a previously
defined instance variable of the same name
*)

let o = new d 2;;       
o#setb 3;;
o#getc;; (* produces 3 *)
o#oldget;; (* produces 2 *)
---

I understand what is happening, but I would prefer is the default semantic was
two merge two values with the same name in an object (giving a type error if
their types can not unify).

Then one could have a syntactic sugar to change the name of some value:

class d x = 
  object
    inherit b x
    inherit c x with v -> v'
  end
;;
To ask to rename the value v from b as v'. Together with the possibility to
bind a name to acces old method, this will allow a total flexibility (I can
always do what I want) which is not the case now.

---

Moreover, the follwing would become possible:

class d =
  object
    inherit b 0 with v -> v0 as b0
    inherit b 1 with v -> v1 as b1
    inherit b 2 with v -> v2 as b2
  end
;;

Christophe Raffalli
Universite de Savoie

PS: do not forget to add "inherit" and "open ... in" for structure in
the next release, that will make some program simpler.