Evolution of object behavior using context relations

ABSTRACT

A collection of design patterns was described by Gamma, Helm, Johnson, and Vlissides in 1994. Recognizing that designs change, each pattern ensures that a certain system aspect can vary over time such as the operations that can be applied to an object or the algorithm of a method. The patterns are described by constructs such as the inheritance and reference relations, attempting to emulate more dynamic relationships. As a result, the design patterns demonstrate how awkward it is to program natural concepts of behavioral evolution when using a traditional object-oriented language.In this paper we present a new relation between classes: the context relation. It directly supports behavioral evolution, and it is meaningful at the analysis, design, and implementation level. At the design level we picture a context relation as a new form of arrow between classes. At the implementation level we use a small extension of C++. The basic idea is that if class C is context-related to a base class B, then B-objects can get their functionality dynamically altered by C-objects. Our language construct for doing this is a generalization of the method update in Abadi and Cardelli's imperative object calculus. A C-object may be explicitly attached to a B-object, or it may be implicitly attached to a group of B-objects for the duration of a method invocation. We demonstrate how the context relation can be used to easily model and program the Adapter, Bridge, Chain of Responsibility, Decorator, Iterator, Observer, State, Strategy, and Visitor patterns.

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INDEX TERMS

Primary Classification:
  D. Software
  D.2 SOFTWARE ENGINEERING
      D.2.m Miscellaneous
          Subjects: Reusable software**

Additional Classification:
  D. Software
  D.1 PROGRAMMING TECHNIQUES
  D.2 SOFTWARE ENGINEERING
        D.2.10 Design**
            Subjects: Representation**
  D.3 PROGRAMMING LANGUAGES
      D.3.2 Language Classifications

          Nouns: C++
      D.3.3 Language Constructs and Features
          Subjects: Data types and structures

General Terms:
Algorithms, Design, Languages