In the object-oriented framework, inheritance is usually presented as a feature that goes hand in hand with subtyping when one organizes abstract datatypes in a hierarchy of classes. However, the two are orthogonal ideas.
- Subtyping refers to compatibility of interfaces. A type B is a subtype of A if every function that can be invoked on an object of type A can also be invoked on an object of type B.
- Inheritance refers to reuse of implementations. A type B inherits from another type A if some functions for B are written in terms of functions of A.
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