Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!pilchuck!dataio!gtenmc!fst
From: fst@gtenmc.UUCP (Fariborz "Skip" Tavakkolian)
Newsgroups: comp.lang.c++
Subject: Re: Passing function pointers in C++
Message-ID: <306@gtenmc.UUCP>
Date: 10 Dec 89 20:12:30 GMT
References: <5115.25805AED@urchin.fidonet.org>
Reply-To: fst@gtenmc.UUCP (Fariborz Skip Tavakkolian)
Organization: GTE Telecon, Inc.  Bothell, WA
Lines: 56

In article <5115.25805AED@urchin.fidonet.org> Roy.Browning@f506.n106.z1.fidonet.org (Roy Browning) writes:
> > From: abbott@aerospace.aero.org (Russell J. Abbott)
> > In article <32106@watmath.waterloo.edu> gjditchfield@watmsg.waterloo.edu 
> > >  ...   In practice, in C++, wouldn't it be simpler to pass a comparison
> > >function as an argument to the sort() function?
> > Can you really do that in C++?  What would the declarations look like?
[deleted]
>Personally I believe that deriving different sorting methods from the base
>class is much cleaner and more in line with OOP.

I have a similar question, or it may be a major confusion in my part.

Say I have a class like this:

class genericField {
protected:
	int length, line, column;
	// here I want something similar to the following three
	int (genericField::*before)();
	int (genericField::*verify)();
	int (genericField::*after)();

public:
	genericField(int len, int ln, int col);
	~genericField();

	virtual int edit(cursesWindow& w);
	void setBefore(int (genericField::*user_before_function)());
	...
};

class dateField : public genericField { ... };
class integerField : public genericField { ... }; // and so on ...

Generally speaking the ``before'' is to be invoked just before editing is
attempted. For example suppose we have

integerField customer_id;
integerField inventory_code;

The ``before'' function for customer_id may make a menu of all allowed
customer ids, and the ``before'' function for inventory_code will make
a list of valid inventory items (from a database for example). As can be
demonstrated each instance of the integerField class may need a different
``before'' function.

Question: how to do this so that a programmer will not need to derive a
new class for each occurrence of a field (i.e. not using virtuals)?

Many thanks
Skip
-- 
----------------------------------------------------------------------------
Fariborz "Skip" Tavakkolian  -of-  Automated Cellular Engineering
Currently consulting         -at-  GTE Telecom, Inc. Bothell, Wa
Mail:                              tiny1!fst@mcgp1  -or-  fst@gtenmc