The Object Model of Objective-PHP

The Object Model of Objective-PHP is based on that of Objective-C which is in turn based on Small-talk 80. Here is a page I Googled which describes the model

and the C source of Objective-C for exploration (very interesting!): http://www.opensource.apple.com/source/objc4/objc4-274/ http://www.opensource.apple.com/source/gcc/gcc-1640/libobjc/

In Objective-PHP each class thus becomes 3 PHP classes. An instance object, a class object and a meta class object. The objects connect together via the isa and super_class pointers.

The instance object contains the actual instance vars (properties, or class variables) and it is this which is created for each new instance of the class you create. This object is cloneable. It contains the isa pointer which points to the class object. (In Objective-C the correlate of this is a struct{} which contains the instance vars)

The class object is a singleton class and the factory of the instance objects. It is created lazily (ie if and when the class is first used) and then lives in memory until termination. It holds the Objective-PHP class’ instance methods. These are the methods that can be called on instance objects and thus can use the instance variables. The class objects super_class pointer points to the class object of the parent (at least this will be the root object) and the isa pointer points to the meta class object

The meta class object is also a singleton. It is created lazily too. It holds the class methods of the class. The isa pointer points to the root meta class object and the super_class pointer to the parent meta class object.

An interesting note: since the root meta class object is infact a subclass of the root class object you CAN send instance method messages defined in the root object to any class object. (see for example Objective-C Pocket Reference)

Document status: INCOMPLETE for current version.