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class cluster

In a class cluster, only an abstract superclass is public. Allocating an instance actually creates

an object of a private subclass. As such, subclassing always happens on an abstract class and

requires all methods to be implemented. See also the class cluster documentation.

"Class clusters are a design pattern that the Foundation framework makes extensive use of.

Class clusters group a number of private concrete subclasses under a public abstract superclass.

The grouping of classes in this way simplifies the publicly visible architecture of an object-oriented

framework without reducing its functional richness. Class clusters are based on the

Abstract Factory design pattern."

Q: 如何子类化(subclass)class cluster?

Q: primitive methods是指什么呢?

ObjC.primitive-methods

Reference

1. Class Clusters - Concepts in Objective-C Programming

https://developer.apple.com/library/ios/documentation/General/Conceptual/CocoaEncyclopedia/ClassClusters/ClassClusters.html

2. Abstract Factory (Todo)

ObjC.class-cluster

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原文地址：http://www.cnblogs.com/cwgk/p/4632547.html