Constrained matchin is type safe

摘要

Temporally ocnstrained matching in a persistent and declarative object-oriented system is introduced as a sesmantic alternative to the existing approaches to the covariance /contravariance problem.While the existing object-oriented type systems are based on subtyping,F-bounded polymorphism and matching,this language system is based entirely on inheritance,which is identified with matching.The type of matching used in htis paper relies on hte tempral constraint system.We prove that this constrained matching guranatees type safe substitutabilty even in situations whee mathcing alone would not.This is possible only because the underlyng formal system is semanticaly much richer than teh paradigms of type systems.Its temporal ocnstraint system cna capture subtleties tha tgo far beyound the level of expressiveness of object-oriented type systems.the temporal nature of the labnguage and its distrincitve orthogonal model of persistence make this language system successful in handling a variety of non-trivial applications.