Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!ulysses!hector!jss
From: jss@hector.UUCP (Jerry Schwarz)
Newsgroups: comp.lang.c++
Subject: Re: address of virtual function (revisited)
Message-ID: <11497@ulysses.homer.nj.att.com>
Date: 8 May 89 14:36:01 GMT
References: <904@garya.Solbourne.COM> <6590114@hplsla.HP.COM>
Sender: netnews@ulysses.homer.nj.att.com
Reply-To: jss@hector.UUCP (Jerry Schwarz)
Organization: AT&T Bell Laboratories
Lines: 42

In article <6590114@hplsla.HP.COM> jima@hplsla.HP.COM (Jim Adcock) writes:
>
>Again, for OOP to be affordable, these simple, everyday "get" and
>"put" type functionalities must be handled at minimal cost.
>Otherwise programmers will violate strict encapsulation, and come
>up with "hack" solutions.

I get a frustrated by assertions of this kind.  By any standard C++
is "affordable", especially when compared to languages like Smalltalk
or Objective C.  Note that the item I am replying to was sumbmitted
only to  comp.lang.c++ so I have to read this as a suggestion that
C++ isn't "affortdable".  (I suppose I could also read this as an
argument for my contention that C++ supports non object
oriented styles and therefore derives its affordability by avoiding
OOP when neccessary, but the tenor of the item I'm replying to
doesn't suggest that reading to me.  I apologize if I'm misreading
Jim Adcocks note.)

In fact, C++ puts you at a low enough level so that (with out
violating the type discipline) it is possible to program the
operation under discussion (finding the "actual" size of an
object) as a simple lookup.

class B  
public
	const size_t	size ;
	B(int i) : Size(i) ;
}  ;

class D : B {
	D(...) : B(sizeof(D)) { ... } 
} ;

	B* p ; ...  p->size ... ; 

Yes, there is a certain amount of pain involved in programming this
explicitly.  But recall that the original complaint was that C++
doesn't provided an "affordable" enough way to do this operation.


Jerry Schwarz
AT&T Bell Labs, Murray Hill