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Re: Programming it's a play

From: Dennis Leeuw
Subject: Re: Programming it's a play
Date: Sun, 21 Sep 2003 13:42:42 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0.0) Gecko/20020623 Debian/1.0.0-0.woody.1

As I am still learning programming the following part is not something I knew. I had wondered what the - sign was for, but had not figured it out yet.

Two types of methods exists as you know : class methods (+) and instances
methods (-). Class methods only works on the class itself, instances methods only works on an instance of a class (ie, an object). imho speaking of "class objects" is a bit misleading -- as the definition of an object is to be an instance of a class... you could send messages directly to the class, but it's not an object per se...

I do want to know what this means. Can someone that writes a class, like the Greeter example write his own Class methods or are Class methods just inherited from the root class. Meaning you can only add instance methods.

What is your view on a class (remember I am a VERY newbie). How can you send a message to a class when a class is not an object.

From the Apple documentation: http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/3objc_language_overview/index.html
I got:
The compiler creates just one accessible object for each class, a class object that knows how to build new objects belonging to the class. (For this reason it's traditionally called a "factory object.") The class object is the compiled version of the class; the objects it builds are instances of the class. The objects that will do the main work of your program are instances created by the class object at runtime.

To get an object to do something, you send it a message telling it to apply a method.
The receiver is an object, and the message tells it what to do.

This to me means that messages can only be send to objects. That a class is the written definition of an object. And that the compiled version is a class object.

The last two sentences are important imho. Since a class is a written definition it can NOT be send a message. You can only send messages to class objects (the compiled version).

Help, help, help it gets more and more confusing.


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