Equality, Identity, and a Modified Contract
نویسندگان
چکیده
This paper describes a software-engineering problem, proposes a solution and shows how that solution influences language design. In many object-oriented programming languages, when implementing equality the programmer has to make sure that it obeys a set of rules, called equality contract. Not only is it difficult to adhere to these seemingly simple rules, but the equality contract itself is a source of potential errors. Even if equality complies with the contract, it can lead to faulty, unintended, indeterministic program behavior. This paper proposes a modified contract that avoids these problems. Additionally, the modified contract describes equality unambiguously, and it implies that equality for values and identity for objects can be regarded as the very same concept. Based on the modified contract the language design can be enhanced in a way that supports value equality and object identity more clearly and more safely.
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