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From: clamage@eng.sun.com (Steve Clamage)
Subject: Re: nested functions
Date: 1999/06/17
Message-ID: <7k9a31$42o$1@engnews1.eng.sun.com>#1/1
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David R Tribble <dtribble@technologist.com> writes:

>I disagree; I don't think it makes much sense to call or pass a
>pointer to a local function to functions outside its scope (i.e,
>outside its enclosing function).

On the contrary, it is very useful. It's common to see a pattern
like this in Pascal (but I'll use C++ syntax):

int main()
{
    void dosomething( bool(*fp)(int), int k )
    {
	...
	if( fp(k) ) // call the callback function
	    ...
	else
	    ...
    }

    void process1()
    {
	... decls

	bool getdata(int i) // the callback for process1
	{
	    ...
	}

	...

	dosomething(getdata);
    }
    ...
}

Function dosomething has a callback that uses its own context.
It can be called from outside the scope of the callback's
enclosing function.

The difference between C++ and Pascal is that Pascal does not
have free pointers to functions. A function can be passed to
another function, but saved in a variable. Consequently, you
cannot call a function with a function whose enclosing scope has
been exited. In C++, that programming error becomes possible.

--
Steve Clamage, stephen.clamage@sun.com
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