ARC

Automatic Reference Counting，自動引用計數。是蘋果公司的Objective-C程序的一種自動內存管理機制，區別於MRC（ManualReference Counting）。在Objective-C編程中，當對象的引用計數為0時，該對象釋放，否則不釋放，運用ARC可以使編程人員基本不用考慮對象何時釋放的問題，編譯器會在合適的時間自動將其引用計數為零。這樣的機制不僅使代碼更簡單並且使程序更穩定，蘋果官方對其的一句解釋“Automatic Reference Counting (ARC) is a compiler feature that provides automatic memory management of Objective-C objects. Rather than having to think about retain and release operations, ARC allows you to concentrate on the interesting code, theobject graphs, and the relationships between objects in your application.”