. We have developed and implemented techniques that double the performance of dynamically-typed object-oriented languages. Our SELF implementation runs twice as fast as the fastest Smalltalk implementation, despite SELF's lack of classes and explicit variables. To compensate for the absence of classes, our system uses implementation-level maps to transparently group objects cloned from the same prototype, providing data type information and eliminating the apparent space overhead for prototype-based systems. To compensate for dynamic typing, user-defined control structures, and the lack of explicit variables, our system dynamically compiles multiple versions of a source method, each customized according to its receiver's map. Within each version the type of the receiver is fixed, and thus the compiler can statically bind and inline all messages sent to self. Message splitting and type prediction extract and preserve even more static type information, allowing the compiler to inline ma...

This paper presents a denotational model of inheritance. The model is based on an intuitive motivation of inheritance as a mechanism for deriving modified versions of recursive definitions. The correctness of the model is demonstrated by proving it equivalent to an operational semantics of inheritance based upon the method lookup algorithm of object-oriented languages.

We propose a new model for flexible composition of objects from a set of features. Features are similar to (abstract) subclasses, but only provide the core functionality of a (sub)class. Overwriting other methods is viewed as resolving feature interactions and is specifi separately for two features at a time. This programming model allows to compose features (almost) freely in a waywhich generalizes inheritance and aggregation. For a set of n features, an exponential number of different feature combinations is possible, assuming a quadratic number of interaction resolutions. We present the feature model as an extension of Java and givetwo translations to Java, one via inheritance and the other via aggregation. We further discuss parameterized features, which work nicely with our feature model and can be translated into Pizza, an extension of Java.

Abstract. We have developed and implemented techniques that double the performance of dynamically-typed object-oriented languages. Our SELF implementation runs twice as fast as the fastest Smalltalk implementation, despite SELF’s lack of classes and explicit variables. To compensate for the absence of classes, our system uses implementation-level maps to transparently group objects cloned from the same prototype, providing data type information and eliminating the apparent space overhead for prototype-based systems. To compensate for dynamic typing, user-defined control structures, and the lack of explicit variables, our system dynamically compiles multiple versions of a source method, each customized according to its receiver’s map. Within each version the type of the receiver is fixed, and thus the compiler can statically bind and inline all messages sent to self. Message splitting and type prediction extract and preserve even more static type information, allowing the compiler to inline many other messages. Inlining dramatically improves performance and eliminates the need to hard-wire low-level methods such as +, ==, and ifTrue:. Despite inlining and other optimizations, our system still supports interactive programming environments. The system traverses internal dependency lists to invalidate all compiled methods

Abstract A multidatabase system (MDBS) is a confederation of pre-existing distributed, heterogeneous, and autonomous database systems. There has been a recent proliferation of research suggesting the application of object-oriented techniques to facilitate the complex task of designing and implementing MDBSs. Although this approach seems promising, the lack of a general framework impedes any further development. The goal of this paper is to provide a concrete analysis and categorization of the various ways in which object orientation has affected the task of designing and implementing MDBSs.

Introduction For the past few years, researchers have been debating the relative merits of object-oriented languages with classes and inheritance as opposed to those with prototypes and delegation. It has become clear that the object-oriented programming language design space is not a dichotomy. Instead, we have identified two fundamental mechanisms---templates and empathy---and several different independent degrees of freedom for each. Templates create new objects in their own image, providing guarantees about the similarity of group members. Empathy allows an object to act as if it were some other object, thus providing sharing of state and behavior. The Smalltalk-80 TM language, 1 Actors, Lieberman's Delegation system, Self, and Hybrid each take differing stands on the forms of templates 1 Smalltalk-80 TM is a trademark of Par

We describe a small set of additions to Scheme to support objectoriented programming, including a form of multiple inheritance. The extensions proposed are in keeping with the spirit of the Scheme language and consequently differ from Lisp-based object systems such as Flavors and the Common Lisp Object System. Our extensions mesh neatly with the underlying Scheme system. We motivate our design with examples, and then describe implementation techniques that yield efficiency comparable to dynamic object-oriented language implementations considered to be high performance. The complete design has an almost-portable implementation, and the core of this design comprises the object system used in T, a dialect of Scheme. The applicative bias of our approach is unusual in object-oriented programming systems. This report describes research done at the Artificial Intelligence Laboratory of the Massachusetts Institute of Technology. Support for the laboratory's artificial intelligence research is ...

. Support for modular evolution of objects is required in many application areas. However, existing mechanisms for incremental behavior composition either do not support evolving objects at all, or do not satisfactorily solve the encapsulation and name collision problems associated with them. In this paper, a new approach to behavior composition in a class-based environment is presented. It is based on the encapsulated object model of class-based inheritance, but introduces an additional abstraction layer between objects and classes. By being responsible for the compositional aspects of the behavior of objects, this layer provides support for the evolution of behavior while at the same time solving the name conflicts that may occur. A formal description of the approach is provided and its feasibility is demonstrated by implementing it as a metalevel extension of Smalltalk-80. 1 Introduction In several object-oriented application areas, support for dynamic and incremental evolution of ...

ion : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 30 3.1.3 Inheritance and Subclassing : : : : : : : : : : : : : : : : : : : : : : : : : : 32 3.1.4 Polymorphism : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 33 3.2 Definitions : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 36 3.2.1 Object-Oriented Language : : : : : : : : : : : : : : : : : : : : : : : : : : : 36 3.2.2 Object-Oriented System : : : : : : : : : : : : : : : : : : : : : : : : : : : : 37 3.3 Summary : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 38 4 Object-Oriented Operating Systems : : : : : : : : : : : : : : : : : : : : : : : : 40 4.1 Definition of an Object-Oriented Operating System : : : : : : : : : : : : : : : : : 40 4.2 Advantages of Object-Oriented Operating Systems : : : : : : : : : : : : : : : : : 43 4.2.1 Portability Advantages : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 43 4.2.2 Code Sharing Adv...

Prototype-based languages are currently proposed as a substitute to class-based languages for a higher flexibility in manipulating objects. These languages are all based on a similar set of basic principles: object-centered representation, dynamic addition (deletion) of slots, cloning and message delegation. But they all differ in the precise interpretation of these principles and nobody has yet considered the semantic issues raised by their combination. In this paper, we propose a new taxonomy of prototypebased languages, enhancing the Treaty of Orlando by now discussing issues associated with the different semantics of the identified prototype-based languages. From this taxonomy, we extract a constructive proposal for the design of a new prototype-based language. This proposal is the chief result of this paper; it suggests one set of primitives which is regarded as the best to provide a clean, useful and coherent prototype-based computational model. We finally describe an implementation of most interesting language alternatives in the form of a Smalltalk-80 platform. This platform establishes an operational semantics for the basic primitives and -- more interesting -- validates our previous taxonomy by implementing it as a class hierarchy. Obviously, this platform has been used to relate in the same formalism the semantics of different languages with each others. For instance, the programming models of existing languages, such as Self, ObjectLisp and Actra's examplars, are faithfully derived as subclasses in this hierarchy.