Associated Objects on Value Types
Greg Parker notes that one should not use objc_setAssociatedObject() to attach associated objects to immutable value-like types such as NSNumber, NSDate, and NSString. The reason is that, due to de-duplication and tagged pointers, the objects may be shared and/or immortal.
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January 18, 2014 6:46 AM
There are also classes which you might not think of as value types which are deduplicated, such as UIFont.
