NSMapTable and NSMutableDictionary differences

Question

Is an NSMapTable the same as an NSMutableDictionary except for allowing keys to be pointers?

Does it differ in memory management?

Answer 1

Be aware that NSMapTable sometimes not deallocates keys and objects if weak-weak, weak-strong or strong-weak bindings are used http://cocoamine.net/blog/2013/12/13/nsmaptable-and-zeroing-weak-references/.

Also in NSMapTable.h you can find that 'entries are not necessarily purged right away when the weak key is reclaimed' :

+ (id)weakToStrongObjectsMapTable NS_AVAILABLE(10_8, 6_0); 
// entries are not necessarily purged right away when the weak key is reclaimed
+ (id)weakToWeakObjectsMapTable NS_AVAILABLE(10_8, 6_0); 
// entries are not necessarily purged right away when the weak key or object is reclaimed