Super and inner

Abstract

In an object-oriented language, a derived class may declare a method with the same signature as a method in the base class. The meaning of the re-declaration depends on the language. Most commonly, the new declaration overrides the base declaration, perhaps completely replacing it, or perhaps using <b>super</b> to invoke the old implementation. Another possibility is that the base class always controls the method implementation, and the new declaration merely augments the method in the case that the base method calls <b>inner</b>. Each possibility has advantages and disadvantages. In this paper, we explain why programmers need both kinds of method redeclaration, and we present a language that integrates them. We also present a formal semantics for the new language, and we describe an implementation for MzScheme.