[racket] Calling Private Methods on non-this Objects?

Oh, if all you want is completely private methods, then use (define/private (m x) ...)  or even plain (define (m x) ...) The latter defines a private field that contains a closure, and you can mutate this field; the former is really a private method and does not consume space in the object. 

I thought you wanted something like 'friendly private', which requires a bit more work. 

-- Matthias



On May 30, 2013, at 7:15 PM, Sean Kanaley wrote:

> This seems like it could work, however if my understanding is correct that any class that wishes C++-style private access has to wrap the class in a module and expose everything except the specific things it's trying to hide, well that seems much more difficult than some sort of define/private that works as C++/Java/C# etc. does.  Perhaps such a feature is not easy to implement, so I don't mean too come across badly, but such a feature would be awfully nice.  Maybe if I feel inspired I can look at the source and try to implement it.
> 
> 
> On Thu, May 30, 2013 at 5:16 PM, Matthias Felleisen <matthias at ccs.neu.edu> wrote:
> 
> Do you know about define-local-member-name?
> 
> #lang racket
> 
> (module server racket
> 
>   (provide c% a)
> 
>   (define-local-member-name a b)
> 
>   (define c%
>     (class object%
>       (field [x 10])
>       (super-new)
>       (define/public (a) x)
>       (define/public (b y) (set! x y)))))
> 
> 
> (module client racket
>   (require (submod ".." server))
> 
>   (define c (new c%))
> 
>   (with-handlers ((exn:fail:object? (lambda (x) (displayln `(message not found)))))
>     (send c b))
>   (displayln (send c a)))
> 
> (require 'client)
> 
>  I think you're looking for it. -- Matthias
> 
> 
> 
> On May 30, 2013, at 3:05 PM, Sean Kanaley <skanaley at gmail.com> wrote:
> 
> > In C++ for example, the following is valid:
> >
> > class A {
> > private:
> >     int test(A a) { return n + a.n; }
> >     int n;
> > };
> >
> > The key point is the "a.n" is valid.
> >
> > I'm trying to create a 3d game in Racket, and in order to avoid recomputing world transforms all the time, child objects (say a rotatable gun on a parent tank) take a parameter to their parent which is used to add the child ("this") to the parent, in order that the parent update a delayed world transform computation in case of multiple calls to set-trans!, roughly:
> >
> > (define obj%
> >   (class object% (super-new) (init ... [parent #f])
> >     (define p parent)
> >     (define cs '())
> >     (when p (send p add-child! this))
> >     (define/public (set-trans! new-t)
> >       ... <includes delayed world-trans calc>
> >       (for ([c cs])
> >         (send c set-trans! (send c local-trans))))
> >     ...
> >     (define/public/private/etc. (add-child! c) (set! cs (cons c cs)))))
> >
> > It obviously works with "define/public", but I'm hoping there is a way to not expose the method everywhere.  It's in essence private, but Racket seems to not allow access even from within the class (send complains "no such method").
> > ____________________
> >  Racket Users list:
> >  http://lists.racket-lang.org/users
> 
> 

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