Subtyping and Inheritance in Object-Oriented Programming

Subtyping and inheritance belong to the major concepts in contemporary object-oriented programming languages, their presence having decisively inuenced the success of the objectoriented paradigm. Inheritance constitutes a technique for reusing code from previous endeavours, while subtyping establishes semantic relationships between object behaviors. Although these, in principle, independent and autonomous notions are rooted in dierent domains of programming, their distinction is poorly understood at large. The necessity is recognized to investigate the notions of types, implementations, subtyping, and inheritance in theory and practice. After presenting these concepts in a language-independent fashion, we contrast subtyping with inheritance, and elaborate the integration of these mechanisms in two dierent object-oriented programming languages. We conclude that the separation is essential both in strongly-typed and dynamically-typed programming languages, facilitating the design in terms of object behaviors to be distinguished from implementation