@package Instance Variables

转自：http://developer.apple.com/library/mac/#releasenotes/Cocoa/RN-ObjectiveC/_index.html

@package is a new instance variable protection class, like @public and @protected. @package instance variables behave as follows:

• @public in 32-bit;

• @public in 64-bit, inside the framework that defined the class;

• @private in 64-bit, outside the framework that defined the class.

In 64-bit, the instance variable symbol for an @package ivar is not exported, so any attempt to use the ivar from outside the framework that defined the class will fail with a link error. See "“64-bit Class and Instance Variable Access Control”" for more about instance variable symbols.