A parallel object-oriented language with inheritance and subtyping
OOPSLA/ECOOP '90 Proceedings of the European conference on object-oriented programming on Object-oriented programming systems, languages, and applications
Strongtalk: typechecking Smalltalk in a production environment
OOPSLA '93 Proceedings of the eighth annual conference on Object-oriented programming systems, languages, and applications
Unifying Genericity - Combining the Benefits of Virtual Types and Parameterized Classes
ECOOP '99 Proceedings of the 13th European Conference on Object-Oriented Programming
On Variance-Based Subtyping for Parametric Types
ECOOP '02 Proceedings of the 16th European Conference on Object-Oriented Programming
C# Language Specification
Adding wildcards to the Java programming language
Proceedings of the 2004 ACM symposium on Applied computing
Variant parametric types: A flexible subtyping scheme for generics
ACM Transactions on Programming Languages and Systems (TOPLAS)
A flow-based approach for variant parametric types
Proceedings of the 21st annual ACM SIGPLAN conference on Object-oriented programming systems, languages, and applications
Reifying wildcards in Java using the EGO approach
Proceedings of the 2007 ACM symposium on Applied computing
Variant path types for scalable extensibility
Proceedings of the 22nd annual ACM SIGPLAN conference on Object-oriented programming systems and applications
Barendregt's Variable Convention in Rule Inductions
CADE-21 Proceedings of the 21st international conference on Automated Deduction: Automated Deduction
A Model for Java with Wildcards
ECOOP '08 Proceedings of the 22nd European conference on Object-Oriented Programming
Java type inference is broken: can we fix it?
Proceedings of the 23rd ACM SIGPLAN conference on Object-oriented programming systems languages and applications
Taming the wildcards: combining definition- and use-site variance
Proceedings of the 32nd ACM SIGPLAN conference on Programming language design and implementation
Taming wildcards in Java's type system
Proceedings of the 32nd ACM SIGPLAN conference on Programming language design and implementation
Variance and generalized constraints for C# generics
ECOOP'06 Proceedings of the 20th European conference on Object-Oriented Programming
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Variance is concerned with the interplay of parametric polymorphism (i.e., templates, generics) and subtyping. The study of variance gives answers to the question of when an instantiation of a generic class can be a subtype of another. In this work, we combine the mechanisms of use-site variance (as in Java) and definition-site variance (as in Scala and C#) in a single type system, based on Java. This allows maximum flexibility in both the specification and use of generic types, thus increasing the reusability of code. Our VarJ calculus achieves a safe synergy of def-site and use-site variance, while supporting the full complexities of the Java realization of variance, including F-bounded polymorphism and wildcard capture. We show that the interaction of these features with definition-site variance is non-trivial and offer a full proof of soundness--the first in the literature for an approach combining variance mechanisms.