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.
This work has been supported in part by the Defense Advanced Research Projects Agency (DARPA) under contract No. NBCH30390004.
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Vaziri, M., Tip, F., Fink, S., Dolby, J. (2007). Declarative Object Identity Using Relation Types. In: Ernst, E. (eds) ECOOP 2007 – Object-Oriented Programming. ECOOP 2007. Lecture Notes in Computer Science, vol 4609. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-73589-2_4
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