Double dispatch in C++

  • Authors:

  • Lorenzo Bettini;Sara Capecchi;Betti Venneri

  • Affiliations:

  • Dipartimento di Sistemi e Informatica, Università di Firenze, Viale Morgagni 65, 50134 Firenze, Italy;Dipartimento di Sistemi e Informatica, Università di Firenze, Viale Morgagni 65, 50134 Firenze, Italy;Dipartimento di Sistemi e Informatica, Università di Firenze, Viale Morgagni 65, 50134 Firenze, Italy

  • Venue:
  • Software—Practice & Experience - Research Articles
  • Year:
  • 2006

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Abstract

Double dispatch is the ability to dynamically select a method not only according to the run-time type of the receiver (single dispatch), but also according to the run-time type of the argument. This mechanism unleashes the power of dynamic binding in object-oriented languages, so enhancing re-usability and separation of responsibilities. However, many mainstream languages, such as, e.g., C++ and Java, do not provide it, resorting only to single dispatch. In this paper we propose an extension of C++ (also applicable to other object-oriented languages) that enables double dispatch as a language feature. This yields dynamic overloading and covariant specialization of methods. We define a translation from the new constructs to standard C++ and we present the preprocessor implementing this translation, called doublecpp. The translated code enjoys static type safety and implements the semantics of double dispatch by using only standard mechanisms of static overloading and dynamic binding, with minimal impact on the performance of the program. Copyright © 2006 John Wiley & Sons, Ltd.