Path: utzoo!utgpu!water!watmath!clyde!att-cb!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!pasteur!ucbvax!hplabs!hp-pcd!hplsla!jima
From: jima@hplsla.HP.COM (              Jim Adcock)
Newsgroups: comp.lang.c++
Subject: Re: Critique of Wiener/Pinson
Message-ID: <6590037@hplsla.HP.COM>
Date: 15 Apr 88 21:03:40 GMT
References: <8063@apple.Apple.Com>
Organization: HP Lake Stevens, WA
Lines: 34

I don't buy the idea that instance variables of an object must always
be accessed via an access method.  I think there are good cases for
violating this "rule".

The simplest case that comes to mind is the overused example of complex
numbers.  To suggest that:

x = myComplexNumber.re();
y = myComplexNumber.im();

is in any way better than:

x = myComplexNumber.re;
y = myComplexNumber.im;

seems ludicrous to me.  In fact, I believe that in many situations similar to
the complex number example, allowing direct access is preferrable to forcing
the class's user to always tag on the "meaningless" () parenthesis.

In any case, I believe the important operative rule that's in effect here
is that the class definer define the public portion of the interface
to his/her class in a way that is not going to change in future revisions
of the class.

If you, the designer, are willing to "guarantee" that those portions of 
your object that you allow access to directly are not going to change in
future revisons of your class, then I say, "no problem, give the class
user direct access."

If you don't feel you can make such a guarantee, then please make sure to
supply access functions instead of allowing direct access to those
instance variables that may be changed in future revisions.

[If in doubt, use access functions]