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PyObjC Architecture
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:authors: Ronald Oussoren

Introduction
------------

XXX: This documented is outdated and incomplete.

This document gives a (brief) description of how the PyObjc package is 
structured. 

Objective-C classes and objects
-------------------------------

Objective-C classes are represented directly as python classes. This allows
us to implement subclassing of Objective-C classes with the full power that
new-style classes provide.

There is one problem with this though, PyTypeObject does not have space to
store additional information, and is a variable-sized object. This means that
subclasses of PyType_Type cannot add instance variables. We solve this by
storing the additional information in a dictionary indexed by the PyTypeObjects
that represent Objective-C classes.

Objective-C objects are represented by proxy objects that are instances of
the classes descriped above.

TODO: work out how we'll implement subclasses objects and describe here.


Methods and instance variables
------------------------------

Methods and instance variables are represented as 'descriptor' objects that
are attributes of the PyTypeObject describing a class. This way it is possible
to use the normal python introspection mechanisms to explore an objective-C
object/class.

There is also a mechanism to call methods that are not part of the advertised
interface of a class. This is needed to support classes like NSProxy that 
forward method invocations to other objects.