An Algebraic Semantics of Subobjects

Abstract

Existing formalisms of inheritance are not sufficient to model the complexities of the kind of multiple inheritance exemplified in C++. Any satisfactory formalism must model the complicating effects of virtual and nonvirtual base classes as well as virtual and non-virtual methods. By abstracting the implementational notion of a subobject and formalizing subobject selection, we develop a formalism to model this combination of features. Not intended as a formal semantics of C++, the resulting model should nevertheless provide an essential level of understanding for language theorists and implementors in their dealings with C++ and related languages. 1 Introduction The style of multiple inheritance first proposed for Simula by Krogdahl[21] and later developed into the C++ multiple inheritance system by Stroustrup[35, 15] exemplifies a particular kind of inheritance in which the underlying imperative is to maintain the integrity of subobjects. Subobjects are historically an implementation...