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From: tim@hoptoad.uucp (Tim Maroney)
Newsgroups: comp.sys.mac.programmer
Subject: Re: MacApp examples Was: Local/AppleTalk Connectivity in MacApp
Message-ID: <14595@hoptoad.uucp>
Date: 7 Jan 91 07:07:38 GMT
References: <34241.27875335@stjhmc.fidonet.org>
Reply-To: tim@hoptoad.UUCP (Tim Maroney)
Organization: Electronics for Imaging, San Bruno CA
Lines: 34

In article <34241.27875335@stjhmc.fidonet.org>
Lawson.English@p88.f15.n300.z1.fidonet.org (Lawson English) writes:
>It should not be necessary for the Application/document classes to know about
>everything: why should they? If they know about a class, and THAT class knows
>about some class that it uses, the interface for the second class need not specify
>a subclass, merely the parent (hopefully something already in MacAPP), THEN
>the implementation section of the second class should use  the Unit of the sub-class
>and typecast the parent class var to the sub-class. This speeds up compile times
>by a factor of 2 or more.

Typecasting is an ugly thing, and one would hope that good object code
would be able to get along without it in most cases.  Sure, you can
reduce dependencies just by making every field of type TObject, and
typecasting as needed, but that's pretty nasty.

Nor does it help to decouple classes from each other (i.e., more
reusable).  If anything, the typecasting solution makes them more
interdependent.

What would really help would be partial type binding in Object Pascal,
so that only fields that are used need to be of a known type.  This
creates problems with the binding of structure offsets, which could be
solved either through a smarter link phase or by the ability to declare
forward classes (so that their sizes are known at the time their owning
class is declared).
-- 
Tim Maroney, Mac Software Consultant, sun!hoptoad!tim, tim@toad.com

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