@property (copy) nsmutablearray *array
-copy, as implemented by mutable Cocoa classes, always returns their immutable counterparts. Thus, when an NSMutableArray is sent -copy, it returns an NSArray containing the same objects.
http://stackoverflow.com/questions/14856681/why-does-a-copy-nonatomic-nsmutablearray-property-create-nsarrays
原文：http://www.cnblogs.com/yibinpan/p/4739842.html