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From: 880716a@aucs.uucp (Dave Astels)
Newsgroups: comp.lang.c++
Subject: Re: indirect message passing
Message-ID: <1990Jun1.114837.11151@aucs.uucp>
Date: 1 Jun 90 11:48:37 GMT
References: <1990May31.131937.25923@aucs.uucp> <41462@brunix.UUCP>
Reply-To: 880716a@aucs.UUCP (Dave Astels)
Organization: School of Computer Science, Acadia Univ., Nova Scotia
Lines: 49

In article <41462@brunix.UUCP> sdm@cs.brown.edu (Scott Meyers) writes:
>In article <1990May31.131937.25923@aucs.uucp> 880716a@aucs.uucp (Dave Astels) writes:
>>I am wondering if it is possible to pass messages in C++ indirectly.
>
>      cout << "Declaring pointers...\n";
>      X *py;
>      py = &y;
>      void (X::*pxmf)();
>      pxmf = X::foo;
>
>      cout << "Calling y.foo() indirectly...";
>      (py->*pxmf)();
>    }  
>

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).

The use of this:  Consider a menu (for example).  There is a CallBack
connected to each option.  When an option is selected its CallBack gets
passed a `Send' message, thus invoking the proper action .. sending a message
to some other object.  This technique enables the construction of a very
sofisticated, event-driven UI with little (if any) programming overhead to
make it run, once the initial set up of all the components is performed.

-- 
- Dave Astels

Internet: 880716a@AcadiaU.CA
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