Prototype of a callback function used to retain a value or key being added to a dictionary.
- iOS 2.0+
- macOS 10.0+
- tvOS 9.0+
- watchOS 2.0+
- Core Foundation
The dictionary’s allocator.
The value being added to the dictionary.
The value or key to store in the dictionary, which is usually the
value parameter passed to this callback, but may be a different value if a different value should be stored in the collection.