Modular session types for distributed object-oriented programming

  • Authors:

  • Simon J. Gay;Vasco T. Vasconcelos;António Ravara;Nils Gesbert;Alexandre Z. Caldeira

  • Affiliations:

  • University of Glasgow, Glasgow, United Kingdom;University of Lisbon, Lisboa, Portugal;University of Lisbon, Lisboa, Portugal;University of Glasgow, Glasgow, United Kingdom;University of Lisbon, Lisboa, Portugal

  • Venue:
  • Proceedings of the 37th annual ACM SIGPLAN-SIGACT symposium on Principles of programming languages
  • Year:
  • 2010

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Abstract

Session types allow communication protocols to be specified type-theoretically so that protocol implementations can be verified by static type-checking. We extend previous work on session types for distributed object-oriented languages in three ways. (1) We attach a session type to a class definition, to specify the possible sequences of method calls. (2) We allow a session type (protocol) implementation to be modularized , i.e. partitioned into separately-callable methods. (3) We treat session-typed communication channels as objects, integrating their session types with the session types of classes. The result is an elegant unification of communication channels and their session types, distributed object-oriented programming, and a form of typestates supporting non-uniform objects, i.e. objects that dynamically change the set of available methods. We define syntax, operational semantics, a sound type system, and a correct and complete type checking algorithm for a small distributed class-based object-oriented language. Static typing guarantees that both sequences of messages on channels, and sequences of method calls on objects, conform to type-theoretic specifications, thus ensuring type-safety. The language includes expected features of session types, such as delegation, and expected features of object-oriented programming, such as encapsulation of local state. We also describe a prototype implementation as an extension of Java.