IsKindOf

IsKindOf is a predicate used in object-oriented programming to determine whether an object's dynamic type is the same as a given class or a subclass of that class. It relies on runtime type information and is commonly used in reflective programming, debugging, serialization, and dynamic dispatch. In many languages, IsKindOf implies a broader check than an exact type match: a positive result may indicate either the specified class or one of its descendants, depending on the language and the specific API.

Semantics and variants vary by language. Some APIs explicitly distinguish between “kind of” and “member of” or exact type checks. For example, in languages with a class hierarchy, a check labeled as IsKindOf typically returns true for instances of the class or any subclass, whereas a check for the exact class would return true only if the object’s class is that class itself.

Language examples illustrate the concept. Objective-C provides a method like isKindOfClass to test whether an object is an instance of a class or any subclass, while isMemberOfClass tests for an exact class. JavaScript uses the instanceof operator to test membership in a prototype chain. Python uses isinstance(obj, Class) to determine if obj is an instance of Class or a subclass, and Ruby offers kind_of? or is_a? for the same purpose.

Usage considerations include balancing safety with polymorphism. Runtime type checks can aid correctness in some contexts but may undermine the benefits of polymorphism or duck typing. They should be used judiciously, especially in performance-critical code or when alternative, behavior-based designs are viable. See also concepts like is-a, isa, and type-check idioms in specific languages.