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From: roman@sparc7.hri.com (Roman)
Newsgroups: comp.lang.c++
Subject: Re: indirect message passing
Message-ID: <1990Jun1.201636.29720@hri.com>
Date: 1 Jun 90 20:16:36 GMT
References: <1990Jun1.114837.11151@aucs.uucp> <1990May31.131937.25923@aucs.uucp> <41462@brunix.UUCP>
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Reply-To: roman@sparc7.hri.com (Roman)
Organization: Horizon Research
Lines: 55

In article <1990Jun1.114837.11151@aucs.uucp>, 880716a@aucs.uucp (Dave
Astels) writes:
> [deleted]
> 
> Yes, but I want to be able to have a class to hold the indirect call, as in:
> 
> class CallBack {
> 	void * instance;	// address of instance to be passed the message 
>     void * method;		// entry point of the method
> public:
> 	CallBack (void *, void *);
> 	Send (void);
> }
> 
> Then I want to be able to set up an indirect call via something like:
> 
> 	CallBack cb (&y, (X::*foo)());   // is the -> member syntax correct ?
> 
> and later perform the call by
> 
> 	cb.Send ();
> 
> I realize that this probably can't work with virtual methods (on first
> consideration), but I don't think that is a problem in my case (the TP
> version won't either, and it works fine for what I need).
> 
>  [deleted]

> - Dave Astels
> 
> Internet: 880716a@AcadiaU.CA
> Bitnet:   880716a@Acadia


The problem is not with virtuals, but with casting a method pointer to
void*. After the
cast the pointer is useless (you loose information necessary to call the
method).

What about this:

class CallBack {
 public:
  virtual void Send();
};
class CallBackX : public CallBack {
	X* objPtr;
	void (X::*fPtr)();
 public:
		CallBackX(X*,void (X::*)());
		void Send() { (objPtr->*fPtr)(); }
};

Unfortunatly for each X you have to define new CallBack class.