Adds a new instance variable to a class.
- iOS 2.0+
- macOS 10.5+
- tvOS 9.0+
- watchOS 2.0+
true if the instance variable was added successfully, otherwise
false (for example, the class already contains an instance variable with that name).
The class must not be a metaclass. Adding an instance variable to a metaclass is not supported.
The instance variable's minimum alignment in bytes is
1<<align. The minimum alignment of an instance variable depends on the ivar's type and the machine architecture. For variables of any pointer type, pass