A collection similar to a dictionary, but with a broader range of available memory semantics.
SDKs
- iOS 6.0+
- macOS 10.5+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 2.0+
Framework
- Foundation
Declaration
class NSMapTable<KeyType, ObjectType> : NSObject where KeyType : AnyObject, ObjectType : AnyObject
Overview
The map table is modeled after NSDictionary with the following differences:
Keys and/or values are optionally held “weakly” such that entries are removed when one of the objects is reclaimed.
Its keys or values may be copied on input or may use pointer identity for equality and hashing.
It can contain arbitrary pointers (its contents are not constrained to being objects).
You can configure an NSMap instance to operate on arbitrary pointers and not just objects, although typically you are encouraged to use the C function API for void * pointers. The object-based API (such as set) will not work for non-object pointers without type-casting.
When configuring map tables, note that only the options listed in NSMap guarantee that the rest of the API will work correctly—including copying, archiving, and fast enumeration. While other NSPointer options are used for certain configurations, such as to hold arbitrary pointers, not all combinations of the options are valid. With some combinations the map table may not work correctly, or may not even be initialized correctly.
Subclassing Notes
NSMap is not suitable for subclassing.