Objective-C : Documentation : Runtime System

Runtime Internals

Some notes on topics to be covered: Data structures: Symtab, Module,

IvarList, MethodList, Category. Info bits. Runtime class lookup.

Ivar lookup. Method lookup. version number. IMP. objc_class.

arglist_t. sarray.

• Method Lookup and Selectors::

• Runtime Initialization::

• Memory Management::

• Metaclasses::

• Archiving and Typed Streams::

• Internal Hash Tables::

Method Lookup and Selectors

objc_msg_lookup. message to self and super.

- Data Type: IMP

The `IMP' data type is a pointer to the function implementing an

Objective-C method.

Runtime Initialization

Memory Management

class_create_instance, object_dispose, object_copy...

For instance, `Object''s `-alloc' method is implemented like this:

+ alloc

{

return class_create_instance(self);

}

Hacking for Efficiency

• Address of a Method::

• Address of an Ivar::

Getting the Address of an Instance Variable