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

From: Robby Findler (robby at eecs.northwestern.edu)
Date: Thu May 30 19:09:40 EDT 2013

When you are inside a class, you don't use send. You just call the method
with a regular function-application looking syntax.

#lang racket
(define c%
  (class object%
    (define/public (m x)
      (printf "n on ~s is ~s\n" x (n x)))
    (define/private (n x)
      (* x x))

(send (new c%) m 11)


On Thursday, May 30, 2013, Sean Kanaley 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").
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