Returns the metaclass definition of a specified class.
- iOS 2.0+
- macOS 10.0+
- tvOS 9.0+
- watchOS 2.0+
The name of the class to look up.
Class object for the metaclass of the named class, or
nil if the class is not registered with the Objective-C runtime.
If the definition for the named class is not registered, this function calls the class handler callback and then checks a second time to see if the class is registered. However, every class definition must have a valid metaclass definition, and so the metaclass definition is always returned, whether it’s valid or not.