Object-oriented Type Systems

A review of the type systems Simula, Smalltalk, C++ and Eiffel, which offers a theory to generalize and explain them. The theory is based upon an idealized object-oriented language called BPOL (Basic Object Programming Language), which explains the common features of all 4 type systems.

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Type systems are required to ensure the reliability and efficiency of software. For object-oriented languages, typing is an especially challenging problem because of inheritance, assignment, and late binding. Existing languages employ different type systems, and it can be difficult to compare, evaluate and improve them, since there is currently no uniform theory for such languages. This book aims to provide such a theory. The authors review the type systems of Simula, Smalltalk, C++ and Eiffel, and present a type system that generalizes and explains them. The theory is based on an idealized object-oriented language called BOPL (Basic Object Programming Language), containing common features of the above languages. A type system, type inference algorithm, and typings of inheritance and genericity are provided for BOPL. Throughout, the results are related to the languages on which BOPL is based.