NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/comp/lang/objectiv/677

Internet Message Format | 1992-11-21 | 1.9 KB

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From: [e-mail] (Carsten Schultz)
Newsgroups: comp.lang.objective-c
Subject: Re: Proper way to access superclass instance variables
Date: 22 Nov 1992 11:58:24 GMT
Organization: ZRZ/TU-Berlin
Lines: 39
Distribution: world
Message-ID: <[e-mail]>
References: <[e-mail]>
Reply-To: [e-mail] (Carsten Schultz)
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In article <[e-mail]> [e-mail]
(Michael Pizolato) writes:
> A question of philosophy.  Consider the following classes:
>
[...]
> I can't think of any good reason to access 'value' directly unless I
have complete control over the implementation of the Foo class.  Even if I
do, it's painful to change every subclass of Foo that might use 'value'
directly if I change Foo as above.
> Any thoughts?

Of course, there's a reason to use the variables directly: it's faster.
But of course it's dangerous to do so, for the reasons you mentioned. In
case of classes you didn't implement yourself, you should only directly
acces variables, if it seems necessary and they're documented. Maybe
someone who doesn't want the variables to be used should declare them
private.

>
> Thanx,
> Michael
>
> P.S.  Given the conclusion that ivars should only ever be accessed
through methods, it seems wrong that they appear in the @interface
section.  Of course we can't change it now, but does anyone know why
they're there?

I always thought, that this is, because the compiler sometimes needs to
know the size of the object; but now that I think about it, I can't think
of an example (at least not with nice Objective-C code).

>
> --
> [e-mail]
> ~18 kyu
> Q16
> NeXTMail appreciated

Carsten