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Variance and Generalized Constraints
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@MISC{Generics_varianceand,
author = {For C Generics and Burak Emir and Andrew Kennedy and Claudio Russo and Dachuan Yu},
title = {Variance and Generalized Constraints},
year = {}
}
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Abstract
Abstract. Generic types in C ♯ behave invariantly with respect to subtyping. We propose a system of type-safe variance for C ♯ that supports the declaration of covariant and contravariant type parameters on generic types. To support more widespread application of variance we also generalize the existing constraint mechanism with arbitrary subtype assertions on classes and methods. This extension is useful even in the absence of variance, and subsumes equational constraints proposed for Generalized Algebraic Data Types (GADTs). We formalize the subtype relation in both declarative and syntax-directed style, and describe and prove the correctness of algorithms for constraint closure and subtyping. Finally, we formalize and prove a type safety theorem for a featherweight language with variant classes and generalized constraints. 1
Keyphrases
generalized constraint generic type type-safe variance constraint closure contravariant type parameter widespread application variant class arbitrary subtype assertion equational constraint type safety theorem featherweight language constraint mechanism generalized algebraic data type syntax-directed style subtype relation
