Multiple Dispatch as Dispatch on Tuples

Many popular object-oriented programming languages, such as C++, Smalltalk-80, Java, and Eiffel, do not support multiple dispatch. Yet without multiple dispatch, programmers find it difficult to express binary methods and design patterns such as the "visitor" pattern. We describe a new, simple, and orthogonal way to add multimethods to single-dispatch object-oriented languages, without affecting existing code. The new mechanism also clarifies many differences between single and multiple dispatch. Keywords Multiple dispatch, multimethods, generic functions, typing, single dispatch, binary methods, semantics, language design, Tuple. 1 INTRODUCTION Single dispatch, as found in C++ [Stroustrup 97], Java [Arnold & Gosling 98, Gosling et al. 96], Smalltalk-80 [Goldberg & Robson 83], and Eiffel [Meyer 92, Meyer 97], selects a method using the dynamic class of one object, the message's receiver. Multiple dispatch, as found in CLOS [Chapter 28, Steele 90] [Paepcke 93], Dylan [Shalit 97, Fei..