Memory management

One feature of the Cocoa environment is its facility for managing dynamically allocated memory. Cocoa's NSObject class, from which most classes, both vendor and user, are derived, implements a reference counting scheme for memory management. Objects derived from the NSObject root class respond to a retain and a release message and keep a retain count which can be queried by sending a retainCount message. A newly allocated object created with alloc or copy has a retain count of one. Sending that object a retain message increments the retain count, while sending it a release message decrements the retain count. When an object's retain count reaches zero, it is deallocated similar to a C++ destructor. dealloc is not guaranteed to be invoked. This reference counting approach is very similar to that of Microsoft's COM, which features the IUnknown interface. IUnknown provides equivalents to retain and release in the form of AddRef and Release.