Java type inference is broken

Smith, Daniel; Cartwright, Robert

doi:10.1145/1449764.1449804

Cited by 27 publications

(24 citation statements)

References 5 publications

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“…For example, the work in [8,7,10,16,47] was mostly focused on researching OO generics, while the work in [18,20,19,21] was focused on type safety. Some research on generics, and generic type inference, was also done after generics were added to Java, e.g., [40,50,4,26].…”

Section: Related Workmentioning

confidence: 99%

Towards a Java Subtyping Operad

AbdelGawad

2017

Proceedings of the 19th Workshop on Formal Techniques for Java-Like Programs

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The subtyping relation in Java exhibits selfsimilarity. The self-similarity in Java subtyping is interesting and intricate due to the existence of wildcard types and, accordingly, the existence of three subtyping rules for generic types: covariant subtyping, contravariant subtyping and invariant subtyping. Supporting bounded type variables also adds to the complexity of the subtyping relation in Java and in other generic nominally-typed OO languages such as C# and Scala.In this paper we explore defining an operad to model the construction of the subtyping relation in Java and in similar generic nominally-typed OO programming languages. Operads, from category theory, are frequently used to model self-similar phenomena. The Java subtyping operad, we hope, will shed more light on understanding the type systems of generic nominally-typed OO languages.

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Section: Related Workmentioning

confidence: 99%

Towards a Java Subtyping Operad

AbdelGawad

2017

Proceedings of the 19th Workshop on Formal Techniques for Java-Like Programs

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“…The same flexibility also proved challenging to both researchers and practitioners. The soundness of wildcards in Java has only recently been proven [4], and the implementation of wildcards has been mired in issues [5,15,16].…”

Section: Related Workmentioning

confidence: 99%

Java Wildcards Meet Definition-Site Variance

Altidor

Reichenbach

Smaragdakis

2012

ECOOP 2012 – Object-Oriented Programming

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Abstract. 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.

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“…The constraint false is never satisfied, and the constraint true is always satisfied. The equivalence constraint S ≡ T is derived as S <: T ∧ T <: S. Following Smith and Cartwright [16], we normalize all constraint formulas into disjunctive normal form and simplify away obvious contradictions and redundancies. We further make use of some auxiliary meta-level definitions, defined in Figure 4.…”

Section: Constraint Formsmentioning

confidence: 99%

Type checking modular multiple dispatch with parametric polymorphism and multiple inheritance

et al. 2011

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In previous work, we presented rules for defining overloaded functions that ensure type safety under symmetric multiple dispatch in an object-oriented language with multiple inheritance, and we showed how to check these rules without requiring the entire type hierarchy to be known, thus supporting modularity and extensibility. In this work, we extend these rules to a language that supports parametric polymorphism on both classes and functions.In a multiple-inheritance language in which any type may be extended by types in other modules, some overloaded functions that might seem valid are correctly rejected by our rules. We explain how these functions can be permitted in a language that additionally supports an exclusion relation among types, allowing programmers to declare "nominal exclusions" and also implicitly imposing exclusion among different instances of each polymorphic type. We give rules for computing the exclusion relation, deriving many type exclusions from declared and implicit ones.We also show how to check our rules for ensuring the safety of overloaded functions. In particular, we reduce the problem of handling parametric polymorphism to one of determining subtyping relationships among universal and existential types. Our system has been implemented as part of the open-source Fortress compiler.

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Java type inference is broken

Cited by 27 publications

References 5 publications

Towards a Java Subtyping Operad

Towards a Java Subtyping Operad

Java Wildcards Meet Definition-Site Variance

Type checking modular multiple dispatch with parametric polymorphism and multiple inheritance

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