Ownership types enforce encapsulation in object-oriented programs by ensuring that objects cannot be leaked beyond object(s) that own them. Existing ownership programming languages either do not support parametric polymorphism (type genericity) or attempt to add it on top of ownership restrictions. Generic Ownership provides perobject ownership on top of a sound generic imperative language. The resulting system not only provides ownership guarantees comparable to established systems, but also requires few additional language mechanisms due to full reuse of parametric polymorphism. We formalise the core of Generic Ownership, highlighting that only restriction ofthis calls and owner subtype preservation are required to achieve deep ownership. Finally we describe how Ownership Generic Java (OGJ) was implemented as a minimal extension to Generic Java in the hope of bringing ownership types into mainstream programming.

Abstract. Data in object-oriented programming is organized in a hierarchy of classes. The problem of object-oriented pattern matching is how to explore this hierarchy from the outside. This usually involves classifying objects by their run-time type, accessing their members, or determining some other characteristic of a group of objects. In this paper we compare six different pattern matching techniques: object-oriented decomposition, visitors, type-tests/type-casts, typecase, case classes, and extractors. The techniques are compared on nine criteria related to conciseness, maintainability and performance. The paper introduces case classes and extractors as two new pattern-matching methods and shows that their combination works well for all of the established criteria. 1

Abstract. Cω extended C # 1.x with a simple, declarative and powerful model of concurrency- join patterns- applicable both to multithreaded applications and to the orchestration of asynchronous, event-based distributed applications. With Generics available in C # 2.0, we can now provide join patterns as a library rather than a language feature. The Joins library extends its clients with an embedded, type-safe and mostly declarative language for expressing synchronization patterns. The library has some advantages over Cω: it is language neutral, supporting other languages like Visual Basic; its join patterns are more dynamic, allowing solutions difficult to express with Cω; its code is easy to modify, fostering experimentation. Although presenting fewer optimization opportunities, the implementation is efficient and its interface makes it trivial to translate Cω programs to C #. We describe the interface and implementation of Joins which (ab)uses almost every feature of Generics. 1

Generic types in C behave invariantly with respect to subtyping.

In the GADT (Generalized Algebraic Data Types) type system, a pattern-matching branch can draw type information from both the scrutinee type and the data constructor type. Even though the type system can handle complex interactions between the two types, most programs require only simple interactions in the form of parametric instantiation and type indexing. To explore the tradeoffs related to GADT patterns, we define the Pointwise GADT type system, which restricts GADTs to the common case of parametric instantiation and type indexing. The Pointwise GADT type system still accepts a wide range of GADT programs, while rejecting a pathological function whose pattern-matching branches can make arbitrarily different assumptions about the type environment. We also state and prove several properties of the type system, which we speculate might be useful in helping researchers design better type inference algorithms.

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