Mutable 對於那些不能直接對其中內容進行更改的類來說，是一種擴展方式，象數值這類的，不涉及到指針的，就沒有 Mutable 子類，可能是因為其本身可以直接修改自身值吧。

換句話說，象字符串這類內容與地址不同且都可以被更改的存儲，在高級語言中，更關心的是內容的更改，尤其象 Java 已經用“引用”淡化了指針的概念，而實際內部是在操作指針這類東西，我也是估計的。

Title Resource Type Topic Framework Date NSMutableArray Class Reference Reference Data Management Data Types & Collections Foundation 2013-10-22 Minor Change NSMutableAttributedString Class Reference Reference Data Management Strings, Text, & Fonts Foundation 2010-02-25 Content Update NSMutableAttributedString UIKit Additions Reference Reference Data Management Strings, Text, & Fonts UIKit 2013-09-18 First Version NSMutableCharacterSet Class Reference Reference Data Management Strings, Text, & Fonts Foundation 2006-05-23 Minor Change NSMutableCopying Protocol Reference Reference Foundation 2006-05-23 Minor Change NSMutableData Class Reference Reference Data Management Data Types & Collections Foundation 2007-03-26 Minor Change NSMutableDictionary Class Reference Reference Data Management Data Types & Collections Foundation 2013-10-22 Minor Change NSMutableIndexSet Class Reference Reference Data Management Data Types & Collections Foundation 2014-02-11 Minor Change NSMutableOrderedSet Class Reference Reference Data Management Data Types & Collections Foundation 2013-10-22 Minor Change NSMutableParagraphStyle Class Reference Reference Data Management Strings, Text, & Fonts UIKit 2013-09-18 Minor Change NSMutableSet Class Reference Reference Data Management Data Types & Collections Foundation 2013-10-22 Minor Change NSMutableString Class Reference Reference Data Management Strings, Text, & Fonts Foundation 2007-03-06 Minor Change NSMutableURLRequest Class Reference Reference Networking & Internet Protocol Streams Foundation 2014-02-11 Minor Change

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