Constraints and Object Identity

Constraint imperative programming is an integration of declarative constraints and imperative object-oriented programming. The primary goal of this integration is to use constraints to express relations among objects explicitly— relations that were implicit in the code in previous languages. However, one of the fundamental concepts of object-oriented programming, object identity, can result in implicit relations, even when explicit identity constraints are supported. We analyze the problem and propose a solution—identity constraints—which we have implemented in our Kaleidoscope’93 language. This solution is understandable, efficiently implementable, and compatible with the Kaleidoscope constraint model. To appear in Proceedings of ECOOP’94 Bologna, Italy, July 1994 Constraints and Object Identity page 1 of 15 Constraints and Object Identity Gus Lopez1, Bjørn Freeman-Benson2, and Alan Borning1 1University of Washington, Dept. of Computer Science & Engineering, FR-35, University of Washington, Seattle, WA 98195, USA, {lopez,borning}@cs.washington.edu 2Århus University, Århus, Denmark. Current address: Carleton University, School of Computer Science, 514 Herzberg Building, 1125 Colonel By Drive, Ottawa, Ontario, Canada, K1S 0G9, [email protected] Abstract. Constraint imperative programming is an integration of declarative constraints and imperative object-oriented programming. The primary goal of this integration is to use constraints to express relations among objects explicitly— relations that were implicit in the code in previous languages. However, one of the fundamental concepts of object-oriented programming, object identity, can result in implicit relations, even when explicit identity constraints are supported. We analyze the problem and propose a solution—identity constraints—which we have implemented in our Kaleidoscope’93 language. This solution is understandable, efficiently implementable, and compatible with the Kaleidoscope constraint model. Constraint imperative programming is an integration of declarative constraints and imperative object-oriented programming. The primary goal of this integration is to use constraints to express relations among objects explicitly— relations that were implicit in the code in previous languages. However, one of the fundamental concepts of object-oriented programming, object identity, can result in implicit relations, even when explicit identity constraints are supported. We analyze the problem and propose a solution—identity constraints—which we have implemented in our Kaleidoscope’93 language. This solution is understandable, efficiently implementable, and compatible with the Kaleidoscope constraint model.