[plt-scheme] protected members in class.ss?

If you use define-local-member-name at the top-level of a module, you
can export the name wherever you wish.

(module m mzscheme
  (require (lib "class.ss"))
  
  (define-local-member-name method-for-my-friends)
  
  (define c%
    (class object%
      (define/public (method-for-my-friends x)
        (printf "x ~s\n" x))
      (super-new)))
  
  (provide c% method-for-my-friends))

(module n mzscheme
  (require m
           (lib "class.ss"))
  (send (new c%) method-for-my-friends 1))


Robby

At Sun, 30 Jul 2006 22:54:52 -0400, Jon Rafkind wrote:
> 
> 
> Robby Findler wrote:
> > At Sun, 30 Jul 2006 19:55:29 -0400, Jon Rafkind wrote:
> >   
> >> Hi,
> >>     I was wondering if there was some way to make a method "protected"
> >> like in C++ and Java wherein a method can only be called by sub-classes.
> >> I read the documentation for class.ss forwards and backwards but didnt
> >> find it.
> >>     
> >
> > There isn't protected ala Java per se, but you can achieve the effect
> > of hiding certain methods (only allowing them in certain scopes) via
> > define-local-member-name. It's a different mechanism, but should help
> > you do what you want (ie, encapsulate).
> >
> >   
> Ok, I suppose that suffices for my purposes but it seems like it might
> be convenient to define classes in separate parts of the program that
> dont have access to the scope that define-local-member-name was used.
> For instance
> 
> ;; im assuming this is how you would use it to achieve protected members.
> ;; parens are totally made up and probably mismatched
> (define-values (base sub1)
>   (let ()
>     (define-local-member-name apple)
>     (let* ((base (class* object% ()
>                          (define/public apple)))
>             (sub1 (class* base ()
>                          (define/public apple)))
>       (values base sub1)))
> 
> ;; some later point in the program
> 
> (define (make-new-thing)
>   (class* base ()
>      (define/public apple)))
> 
> Maybe I'm just thinking to much in the Java/C++ OOP way?