Re: [Caml-list] Optional arguments in inherited methods

[John Goerzen <jgoerzen@complete.org>]

On Wed, Apr 28, 2004 at 09:56:36AM -0700, james woodyatt wrote:
> 	method getdataf sname = <code here returns function>
> 
> ...you wish the compiler to insure that the default values are used for 
> each of the optional arguments in the [possibly partial] evaluation of 
> the derived class method.
> 
> Well? it doesn't.  You have to define the derived class method in two 
> parts.

Hmm.  I worked around that problem but now I have a new one.  From my
.mli file, I have this in my superclass:

    method get: ?default:string -> string -> string -> string

and I wish to have this in my subclass:

    method get: ?default:string -> ?raw:bool -> ?idepth:int -> 
          ?extravars:(string, string) Hashtbl.t 
          -> string -> string -> string
                      
Now, since labeled args are not positional, I would think that the
compiler should have no problem with adding new optional args, since a
call to the base class's method would remain completely valid as a call
to the subclass's method.  However, I get this error:

The method get has type
  ?default:string ->
  ?raw:bool ->
  ?idepth:int ->
  ?extravars:(string, string) Hashtbl.t -> string -> string -> string
but is expected to have type ?default:string -> string -> string -> string

Argh.  Does OCaml's object system really not support adding additional
optional variables to subclass methods?

That would be rather annoying if true.

-- John

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