How to remove elements in NSMutableArray or NSMutableDictionary during enumeration?

Since you can't remove objects from an array or dictionary during enumeration, you'll have to accumulate the items you want to delete, and then delete them all after the enumeration.

Whether you build up an index set during enumeration, or modify the array itself during enumeration, you will have to give up NSEnumerationConcurrent, because most Cocoa objects cannot safely be modified simultaneously from multiple threads.

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