Equal rights for functional objects or, the more things change, the more they are the same

Abstract

We argue that intensional object identity in object-oriented programming languages and databases is best defined operationally by side-effect semantics. A corollary is that "functional" objects have extensional semantics. This model of object identity, which is analogous to the normal forms of relational algebra, provides cleaner semantics for the value-transmission operations and built-in primitive equality predicate of a programming language, and eliminates the confusion surrounding "call-by-value" and "call-by-reference" as well as the confusion of multiple equality predicates.Implementation issues are discussed, and this model is shown to have significant performance advantages in persistent, parallel, distributed and multilingual processing environments. This model also provides insight into the "type equivalence" problem of Algol-68, Pascal and Ada.