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Objective-C Programming: The Big Nerd Ranch Guide by Mikey Ward, Aaron Hillegass

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24 Collection Classes

A collection class is one whose instances hold pointers to other objects. You have already used two collection classes: NSArray and its subclass NSMutableArray. In this chapter, you will delve deeper into arrays and learn about some other collection classes: NSSet/NSMutableSet and NSDictionary/NSMutableDictionary.

NSSet/NSMutableSet

A set is a collection that has no sense of order, and a particular object can only appear in a set once.

Sets are primarily useful for asking the question Is it in there? For example, you might have a set of URLs that are not child-appropriate. Before displaying any web page to a child, you would do a quick check to see if the URL is in the set. Sets are faster at ...

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