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07:53, 13 January 2012 In object-oriented programming, a metaclass is a class whose instances are classes.
Just as an ordinary class defines the behavior of certain objects, a metaclass defines the behavior of certain classes and their instances. Not all object-oriented programming languages support metaclasses.
Among those that do, the extent to which metaclasses can override any given aspect of class behavior varies.
Each language has its own metaobject protocol, a set of rules that govern how objects, classes, and metaclasses interact.