Ownership confinement ensures representation independence for object-oriented programs

  • Authors:

  • Anindya Banerjee;David A. Naumann

  • Affiliations:

  • Kansas State University, Manhattan, Kansas;Stevens Institute of Technology, Hoboken, New Jersey

  • Venue:
  • Journal of the ACM (JACM)
  • Year:
  • 2005

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Abstract

Representation independence formally characterizes the encapsulation provided by language constructs for data abstraction and justifies reasoning by simulation. Representation independence has been shown for a variety of languages and constructs but not for shared references to mutable state; indeed it fails in general for such languages. This article formulates representation independence for classes, in an imperative, object-oriented language with pointers, subclassing and dynamic dispatch, class oriented visibility control, recursive types and methods, and a simple form of module. An instance of a class is considered to implement an abstraction using private fields and so-called representation objects. Encapsulation of representation objects is expressed by a restriction, called confinement, on aliasing. Representation independence is proved for programs satisfying the confinement condition. A static analysis is given for confinement that accepts common designs such as the observer and factory patterns. The formalization takes into account not only the usual interface between a client and a class that provides an abstraction but also the interface (often called “protected”) between the class and its subclasses.