classof

Classof is a term used in programming to denote an operation or function that returns the class of a given object at runtime. It is a form of reflective capability found in many dynamic or introspective languages, and its exact name and return value vary by language.

Naming variants and scope vary across languages. Common variants include class-of, class_of, and classOf. The concept spans languages with different naming conventions and type systems. In Common Lisp, for example, class-of is a standard function that returns the class object of its argument, enabling further reflection or dynamic dispatch based on an object's runtime type. In languages with camelCase conventions or library extensions, similar functionality may be exposed as classOf or a related API. In Python, a closely related concept is obj.__class__ or type(obj), which yields the object's class.

Typical uses of classof include debugging, generic programming, and the implementation of type-based dispatch or behavior that depends on an object's runtime type. The class object obtained can be compared, queried for attributes, or used to look up methods in reflective systems.

Limitations and variations exist. Not all languages provide a distinct class-of operation, and in statically typed languages, runtime type information may be limited or controlled by the language’s reflection facilities. In complex systems with metaclasses or multiple inheritance, the meaning of “the class” can be nuanced, and the returned value may reflect the most specific class, its metaclass, or another classification depending on the language.

See also: type, getClass, reflection, metaclass, class (in object-oriented programming).