"Object-Oriented Programming" and "Data Abstraction" have become very common terms. Unfortunately, few people agree on what they mean. I will offer informal definitions that appear to make sense in the context of languages like Ada, C++, Modula2, Simula, and Smalltalk. The general idea is to equate "support for data abstraction" with the ability to define and use new types and equate "support for object-oriented programming" with the ability to express type hierarchies. Features necessary to support these programming styles in a general purpose programming language will be discussed. The presentation centers around C++ but is not limited to facilities provided by that language.

We describe the support to object management of the distributed object-oriented operating system SOS. We discuss the integration of object migration and storage into C++ programs, a language not designed for that purpose. The necessary support is split between the compiler and a run-time object management system. Migration and storage preserve the type and structure of the objects, which may be user-defined and arbitrarily complex. Our mechanisms are simple, generic, and require little programmer intervention. The key elements are dynamic classes, a generalized pointer type which allows to efficiently refer to an object, pre-requisite objects, and a mechanism for object re-initialization. Keywords: persistence, migration, dynamic linking, dynamic type-checking, C++, object-oriented operating system, SOS 1 INTRODUCTION We present some aspects of the object management support in the SOS operating system [Sha86a]. SOS is a research program to build a distributed operating system, where ...

Abstract. All organizational functions carried out by classes can be accomplished in a simple and natural way by object inheritance in classless languages, with no need for special mechanisms. A single model—dividing types into prototypes and traits—supports sharing of behavior and extending or replacing representations. A natural extension, dynamic object inheritance, can model behavioral modes. Object inheritance can also be used to provide structured name spaces for well-known objects. Classless languages can even express “class-based ” encapsulation. These stylized uses of object inheritance become instantly recognizable idioms, and extend the repertory of organizing principles to cover a wider range of programs. 1

There are numerous times when a C ++ user could benefit from a pointer variant that has more functionality than is provided by the basic, language-defined pointer. For example, type-accurate garbage collection, reference counting, or transparent references to distributed or persistent objects, might be implemented with classes that provide pointer functionality. The C ++ language directly supports one kind of pointer substitute, the smart pointer, in the form of overloadable indirection operators: -? and . In this paper we evaluate how seamlessly smart pointers can replace raw pointers. The ideal is for client code not to care whether it is using raw pointers or smart pointers. For example, if a typedef selects whether raw or smart pointers are used throughout the program, changing the value of the typedef should not introduce syntax errors. Unfortunately, C ++ does not support pointer substitutes well enough to permit seamless integration. This paper presents the desired behavi...

Abstract. The design of inheritance and encapsulation in SELF, an object-oriented language based on prototypes, results from understanding that inheritance allows parents to be shared parts of their children. The programmer resolves ambiguities arising from multiple inheritance by prioritizing an object’s parents. Unifying unordered and ordered multiple inheritance supports differential programming of abstractions and methods, combination of unrelated abstractions, unequal combination of abstractions, and mixins. In SELF, a private slot may be accessed if the sending method is a shared part of the receiver, allowing privileged communication between related objects. Thus, classless SELF enjoys the benefits of class-based encapsulation. 1

Garbage collection is an extremely useful programming language feature that is currently absent from C++. The benefits from garbage collection include convenience and safety because the programmer is not responsible for freeing dynamically allocated storage. Many reclamation schemes improve efficiency by compacting objects in memory improving locality and reducing paging. Some reclamation techniques are more efficient than manual reclamation for important classes of data structures. This paper presents a copying collector for C++ that supports polymorphism and does not require indirection through an "object table." This memory reclamation scheme is one of few that is philosophically consistent with the design goals of the C++ programming language: one must not be penalized for features that are not used. This report includes performance measurements from a prototype implementation. Introduction Garbage collection (GC) is a programming environment feature that removes the programmer 's...

The goal of this work is to provide uniform transparent access to objects, be they local, remote, persistent, or mobile. In this way, we facilitate distributed programming and persistence management. An object (the target) is accessed through a reference. A reference retains its meaning as it is copied, stored, passed in messages, and as the target migrates. A reference is used to invoke a procedure (or method) of the target object. References support standard single-space targets, as well as fragmented objects [9]. The cost of using a reference to a local object is comparable to the cost of accessing the object through a pointer. In the implementation, a reference is a chain of links. Each link embodies a small piece of functionality. A chain may be composed of an arbitrary number of links.

Structured graphics is useful for building applications that use a direct manipulation metaphor. Objectoriented languages offer inheritance, encapsulation, and runtime binding of operations to objects. Unfortunately, standard structured graphics packages do not use an object-oriented model, and object-oriented systems do not provide general-purpose structured graphics, relying instead on low-level graphics primitives. An object-oriented approach to structured graphics can give application programmers the benefits of both paradigms. We have implemented a two-dimensional structured graphics library in C++ that presents an object-oriented model to the programmer. The graphic class defines a general graphical object from which all others are derived. The picture subclass supports hierarchical composition of graphics. Programmers can define new graphical objects either statically by subclassing or dynamically by composing instances of existing classes. We have used both this library and an...

An associative array is a one-dimensional array of unbounded size whose subscripts can be non-integral types such as character strings. Traditionally associated with dynamically typed languages such as AWK and SNOBOL4, associative arrays have applications ranging from compiler symbol tables to databases and commercial data processing. This paper describes a family of C + class definitions for associative arrays, including programming examples, application suggestions, and notes on performance. It concludes with a complete programming example which serves the same purpose as a well-known system command but is much smaller and simpler. 1.

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