@public means an instance variable can be accessed "directly" with -> from
outside the object. It essentially makes the object's values accessible as
if it were a C struct. It gives quick access to values, but is dangerous
because you might accidentally change values. By default, IVARS are
"private" and the usage like anObject->x will be rejected by the compiler.
THe "object oriented religion" holds that people should not write code
this way, but sometimes you can get speedups if you avoid it. If you
constantly have to do [anObject getValue] you impose more overead on the
runtime than if you have a public variable obtained with anObject -> x.
In the Pentium 75 days, a few hundred thousand of those would really add
up. But I've not noticed it so much lately :;
The #import (or include) includes a header file where a class and its
methods are defined. It tells the compiler where to look for methods.
If you use @class Abc, you are not really including a class, but you are
promising the compiler that you will define it later. THat silences the
warnings. This is used as a way to avoid "circular includes". You can't
include two h files in each other. Suppose there are 2 classes.
A.h A.m
B.h B.m
In A.h, you want to declare a variable
B * myThing;
If B.h imports A.h, you can't import B.h in A.h, The compiler is confused
because, whichever one gets found first by the compiler will fail because
it can't find the o file for the other. So to fool the compiler, you
promise it that class will come along later. I recall using that trick in
a couple of projects, but I never found a full manual length treatment of
it.
The alternative work around is, in A.h, to declare
id myThing;
and then import B.h in A.m. Then the compiler might not get too confused
about where it is supposed to find methods for myThing.
I say might not because the newest gcc seems to whine and complain and
warn about everything, even stuff we've been doing since before the dawn
of time. Or the introduction of the Pentium, which ever came first :)
I hope I've not misled you. I'm just giving you back the information I've
gleaned from conversations in this list.
pj
Derek Farren wrote:
Hello Swarm friends.
What´s the difference between includeing a Class named Abc by "#include
Abc.h" and @class Abc?
Also, what does @public before the definition of a variable mean?
Thanks, Derek
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