Path: utzoo!utgpu!watserv1!watmath!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!usc!jarthur!nntp-server.caltech.edu!woody
From: woody@nntp-server.caltech.edu (William Edward Woody)
Newsgroups: comp.sys.mac.programmer
Subject: Re: C++ vs Think C 4.0 Question
Message-ID: <1990Nov29.181707.25001@nntp-server.caltech.edu>
Date: 29 Nov 90 18:17:07 GMT
References: <1990Nov27.040144.27236@cunixf.cc.columbia.edu> <1990Nov27.163703.1323@actrix.gen.nz>
Organization: California Institute of Technology, Pasadena
Lines: 87

In article <1990Nov27.163703.1323@actrix.gen.nz> Bruce.Hoult@bbs.actrix.gen.nz writes:
>In article <1990Nov27.040144.27236@cunixf.cc.columbia.edu> jtt@cunixd.cc.columbia.edu (James T. Tanis) writes:
>> I'm interested in learning c++, but in reading various stuff about it, I
>> have
>> yet to encounter the "inherited" scope specifier, ubiquitous in TCL
>> programs. Is there, in fact, no way in 'real' c++ to just call the same
>> function in a base class?
>
>Correct.  Standard C++ doesn't have the "inherited" keyword.  Apple have added
>it to their MPW C++ compiler, but only for objects derived from the special
>base class "PascalObject".  They didn't allow it in general useage because
>they wanted to "avoid making gratuitous changes to C++".
>
>I'd like to see it as well.


Actually, if you have the following declarations:

	class TObject1 {
	    public:
		virtual void foo();
	};

	class TObject2: public TObject1 {
	    public:
			void foo();
	};

the following is legal and does what you want in both MPW C++ and Turbo C++
on the IBM PC (don't ask why I'm using a PC; it's a horrible story):

	void TObject2::foo()
	{
	    TObject1::foo();		/* Will call TObject1::foo() */
	}

The extension keyword 'inherited' simply did the following:

	void TObject2::foo()
	{
	    inherited::foo();		/* Will call TObject1::foo() */
	}

The problem with this keyword is when you have multiple inheritance.  For
example:

	class TObject1 {
	    public:
		virtual void foo();
	};

	class TObject2 {
	    public:
		virtual void foo();
	};

	class TObject3: public TObject1, public TObject2 {
	    public:
			void foo();
	};

and in TObject3::foo() you say:

	void TObject3::foo()
	{
	    inherited::foo();
	}

do you mean TObject1::foo() or TObject2::foo()?

C++ requires that you expressly indicate which function you are calling.
This is only a minor price to pay, IMHO, for the value of multiple
inheritance.

				-- Bill

Disclamer:  none of the code above was tested, but the examples were taken
from memory of actual working code.  Further, I don't know why you
would ever want to do the second example above, but I suppose it can
come up in actual code.  Your milege will vary.  Do not remove back
panel; no serviceable parts inside.

-- 
	William Edward Woody		   | Disclamer:
USNAIL	P.O.Box 50986; Pasadena, CA 91115  |
EMAIL	woody@tybalt.caltech.edu	   | The useful stuff in this message
ICBM	34 08' 44''N x 118 08' 41''W	   | was only line noise.