Thursday, January 16, 2014 [Tweets] [Favorites]

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.

2 Comments

There are also classes which you might not think of as value types which are deduplicated, such as UIFont.

@Jens Yes, fonts too, since the documentation says they are immutable and “These methods check for an existing font object with the specified characteristics and return it if it exists.”

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