Translating Double Dispatch into Single Dispatch

  • Authors:

  • Lorenzo Bettini;Sara Capecchi;Betti Venneri

  • Affiliations:

  • Dipartimento di Sistemi e Informatica, Università di Firenze, Via Lombroso 6/17, 50134 Firenze, Italy;Dipartimento di Sistemi e Informatica, Università di Firenze, Via Lombroso 6/17, 50134 Firenze, Italy;Dipartimento di Sistemi e Informatica, Università di Firenze, Via Lombroso 6/17, 50134 Firenze, Italy

  • Venue:
  • Electronic Notes in Theoretical Computer Science (ENTCS)
  • Year:
  • 2005

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Abstract

Goals of flexibility and re-usability in typed object-oriented languages suggest the requirement of double dispatch, i.e., the mechanism of dynamically selecting a method not only according to the run-time type of the receiver (single dispatch), but also to the run-time type of the argument. However, many mainstream languages, such as, e.g., C++ and Java, do not provide it, resorting to only single dispatch. In this paper we present a general technique for adding double dispatch as a type-safe language feature, so yielding dynamic overloading and covariant specialization of methods, without extending basic semantics. To this aim we introduce a toy core language, extended to a full form of (non encapsulated) multi methods. Then we define a translation algorithm from multi methods to the core language, that implements double dispatch by using only standard mechanisms of static overloading and single dispatch. As a main feature, our translation preserves type safety, it uses neither RTTI nor type downcasts and does not introduce crucial overhead during method selection.