Declarative object identity using relation types

  • Authors:

  • Mandana Vaziri;Frank Tip;Stephen Fink;Julian Dolby

  • Affiliations:

  • IBM T. J. Watson Research Center, Yorktown Heights, NY;IBM T. J. Watson Research Center, Yorktown Heights, NY;IBM T. J. Watson Research Center, Yorktown Heights, NY;IBM T. J. Watson Research Center, Yorktown Heights, NY

  • Venue:
  • ECOOP'07 Proceedings of the 21st European conference on Object-Oriented Programming
  • Year:
  • 2007

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Abstract

Object-oriented languages define the identity of an object to be an address-based object identifier. The programmer may customize the notion of object identity by overriding the equals() and hashCode() methods following a specified contract. This customization often introduces latent errors, since the contract is unenforced and at times impossible to satisfy, and its implementation requires tedious and error-prone boilerplate code. Relation types are a programming model in which object identity is defined declaratively, obviating the need for equals() and hashCode() methods. This entails a stricter contract: identity never changes during an execution. We formalize the model as an adaptation of Featherweight Java, and implement it by extending Java with relation types. Experiments on a set of Java programs show that the majority of classes that override equals() can be refactored into relation types, and that most of the remainder are buggy or fragile.