[Caml-list] classes and labels

[Caml-list] classes and labels

[wester]

Hi,

I have the class definition:

# class myclass ?(n=0) () =
  object  
   val nn = n;
   method get_nn = nn
   method clone (na: int) = let (mc: myclass) = new myclass ~n:na () in mc;
end;;
 
that produces the following error message in the toplevel:

          Characters 5-153:
The expression "new myclass" has type ?n:int -> unit -> myclass
but is used with type int -> unit -> myclass

Can sombody tell what is wrong with my class definition?
I would be very apprecitative for any help.

With kind regards

Rolf Wester
-------------------------------------
Rolf Wester
wester@ilt.fhg.de
-------------------
To unsubscribe, mail caml-list-request@inria.fr.  Archives: http://caml.inria.fr

Re: [Caml-list] classes and labels

[Gerd Stolpmann]

On Tue, 20 Mar 2001, wester@ilt.fhg.de wrote:
>Hi,
>
>I have the class definition:
>
># class myclass ?(n=0) () =
>  object  
>   val nn = n;
>   method get_nn = nn
>   method clone (na: int) = let (mc: myclass) = new myclass ~n:na () in mc;
>end;;
> 
>that produces the following error message in the toplevel:
>
>          Characters 5-153:
>The expression "new myclass" has type ?n:int -> unit -> myclass
>but is used with type int -> unit -> myclass
>
>Can sombody tell what is wrong with my class definition?

Nothing. It is a restriction of O'Caml 3.00. Your class definition works fine 
in 3.01. If you cannot upgrade, this is the workaround:

# class myclass ?(n=0) () =
  object  
   val nn = n;
   method get_nn = nn
   method clone (na: int) = 
     let (mc: myclass) = new myclass ?n:(Some na) () in mc; 
  end;;

Gerd
-- 
----------------------------------------------------------------------------
Gerd Stolpmann      Telefon: +49 6151 997705 (privat)
Viktoriastr. 100             
64293 Darmstadt     EMail:   gerd@gerd-stolpmann.de
Germany                     
----------------------------------------------------------------------------
-------------------
To unsubscribe, mail caml-list-request@inria.fr.  Archives: http://caml.inria.fr

Re: [Caml-list] classes and labels

[Jacques Garrigue]

From: wester@ilt.fhg.de

> class myclass ?(n=0) () =
>   object  
>    val nn = n;
>    method get_nn = nn
>    method clone (na: int) = let (mc: myclass) = new myclass ~n:na () in mc;
> end;;
>  
> that produces the following error message in the toplevel:
> 
>           Characters 5-153:
> The expression "new myclass" has type ?n:int -> unit -> myclass
> but is used with type int -> unit -> myclass

What version of ocaml are you using ?

At least, I couldn't reproduce the problem with 3.01:

        Objective Caml version 3.01

# class myclass ?(n=0) () =
    object  
     val nn = n;
     method get_nn = nn
     method clone (na: int) = let (mc: myclass) = new myclass ~n:na () in mc;
    end;;
class myclass :
  ?n:int ->
  unit ->
  object val nn : int method clone : int -> myclass method get_nn : int end

And this both with the -labels option on and off.
By the way, you don't need all these annotations in the clone method:
 method clone na = new myclass ~n:na ()

Regards,

Jacques Garrigue
-------------------
To unsubscribe, mail caml-list-request@inria.fr.  Archives: http://caml.inria.fr