Alan Snyder

Encapsulation and inheritance in object-oriented programming languages

Object-oriented programming is a practical and useful programming methodology that encourages modular design and software reuse. Most object-oriented programming languages support data abstraction by preventing an object from being manipulated except via its defined external operations. In most languages, however, the introduction of inheritance severely compromises the benefits of this encapsulation. Furthermore, the use of inheritance itself is globally visible in most languages, so that changes to the inheritance hierarchy cannot be made safely. This paper examines the relationship between inheritance and encapsulation and develops requirements for full support of encapsulation with inheritance.

Experience with CommonLoops

CommonLoops is an object-oriented language embedded in Common Lisp. It is one of two such languages selected as starting points for the Common Lisp Object System (CLOS) which is currently being designed as a standard object-oriented extension to Common Lisp. This paper reports on experiences using the existing Portable CommonLoops (PCL) implementation of CommonLoops. The paper is divided into two parts: a report on the development of a window system application using the CommonLoops programming language, and a description of the implementation of another object-oriented language (CommonObjects) on top of the CommonLoops metaclass kernel, paralleling the two aspects of CommonLoops: the programming language and the metaclass kernel. Usage of the novel features in CommonLoops is measured quantitatively, and performance figures comparing CommonLoops, CommonObjects on CommonLoops, and the native Lisp implementation of CommonObjects are presented. The paper concludes with a discussion about the importance of quantitative assessment for programming language development.

Modeling the C++ object model

We are developing an abstract model to provide a framework for comparing the object models of various systems, ranging from object-oriented programming languages to distributed object architectures. Our purpose is to facilitate communication among researchers and developers, improve the general understanding of object systems, and suggest opportunities for technological convergence. This paper describes the application of the abstract object model to the C++ programming language. We give an overview of the abstract object model and illustrate its use in modeling C++ objects. Several modeling alternatives are discussed and evaluated, which reveal anomalies in the C++ language. We conclude by characterizing those aspects of the C++ object model that distinguish C++ from other object systems.

Language level persistence for an object-oriented application programming platform

A description is given of a prototype persistent-object system, called DOOM, (Data-Oriented Object Manager), which was designed to explore issues in language-level persistence for object-oriented application platforms. In its first iteration, the language aspects of persistence were investigated, and a design which allowed the exchange of persistent objects between Common Objects (Common Lisp extension) and Objective-C/sup 2/ (C extension) was implemented. The system features a tight coupling between the languages; run-time support and a relational storage manager. In a second iteration, the coupling between the database and the language was loosened, and more characteristics of the database were exposed to the applications programmer. The language extensions introduced into CommonObject and Objective-C/sup 2/ to support persistence are discussed, and the architectures of DOOM-I and DOOM-II are described. Some persistent-object systems similar to DOOM that have appeared in the recent literature are briefly reviewed, and DOOM is examined in the light of two of the other systems.<<ETX>>