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From: Terry Lambert <tlambert@primenet.com>
Message-Id: <199712120242.TAA07290@usr02.primenet.com>
Subject: Re: Why so many steps to build new kernel?
To: j_mini@efn.org
Date: Fri, 12 Dec 1997 02:42:07 +0000 (GMT)
Cc: jkh@time.cdrom.com, ksmm@cybercom.net, freebsd-hackers@FreeBSD.ORG
In-Reply-To: <19971211021856.61158@micron.mini.net> from "Jonathan Mini" at Dec 11, 97 02:18:56 am
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>  3) C++ does not implement data hiding. Sure, you have opaque structs,
> but you cannoy make an opaque class. That is, you cannot have a class
> defined where you know how to interface with the functions, but not
> the details of the internal data. Because you have to define the
> private data within the same scope as the public interface, private
> datatypes aren't possible.

This is incorrect.

global.h:

	#define interface struct	/* no virtual destructor needed*/


myOpaqueClass.h:

	interface myOpaqueClass {
		virtual int function1( int arg1, char *arg2) = 0;
		virtual int function2( char *arg1) = 0;
	};

	extern myOpaqueClass *createOpaqueClassObject();

myImplementationClass.cc

	#include "global.h"
	#include "myOpaqueClass.h"

	class myImplementationClass : public myOpaqueClass {
	private:
		/*
		 * Private data not defined in the scope of the
		 * public interface.
		 */
		int	somedata;

	public:
		myImplementationClass();		/* constructor*/
		~myImplementationClass();		/* destructor*/
		int function1( int arg1, char *arg2);
		int function2( char *arg1);
	};

	/*
	 * Public interface; use shared object technology to select
	 * between implementation class instances for a given opaque
	 * class...
	 */

	myOpaqueClass *
	createOpaqueClassObject()
	{
		myImplementationClass	*instance;

		intstance = new myImplementationClass;

		return( (myOpaqueClass *)instance;
	}


	/*
	 * constructor
	 */
	myImplementationClass::myImplementationClass()
	{
	}

	/*
	 * destructor
	 */
	myImplementationClass::myImplementationClass()
	{
	}

	/*
	 * implementation class specific implementation of pure
	 * virtual base class interface "function1"...
	 */
	int
	myImplementationClass::function1( int arg1, char *arg2))
	{
		...
	}

	/*
	 * implementation class specific implementation of pure
	 * virtual base class interface "function2"...
	 */
	int
	myImplementationClass::function2( char *arg1)
	{
		...
	}


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.