Object-oriented programming versus abstract data types

Cook, William R.

doi:10.1007/bfb0019443

Cited by 68 publications

(51 citation statements)

References 39 publications

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“…(In fact, the same example is used in the Appendix of (Reynolds, 1978) to make the same point.) See (Reynolds, 1981b;Tennent, 1991) for discussion of Algol-like languages, and (Reynolds, 1975;Cook, 1991) for comparisons of linguistic approaches to representational abstraction. To a certain extent, the relevance of representational abstraction to the semantics of local variables has already been exploited.…”

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confidence: 99%

Parametricity and Local Variables

O’Hearn¹,

Tennent²

1997

Algol-Like Languages

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We propose that the phenomenon of local state may be understood in terms of Strachey's concept of parametric (i.e., uniform) polymorphism. The intuitive basis for our proposal is the following analogy: a non-local procedure is independent of locally-declared variables in the same way that a parametrically polymorphic function is independent of types to which it is instantiated.A connection between parametricity and representational abstraction was rst suggested by J.C. Reynolds. Reynolds used logical relations to formalize this connection in languages with type variables and user-de ned types. We use relational parametricity to construct a model for an Algol-like language in which interactions between local and non-local entities satisfy certain relational criteria. Reasoning about local variables essentially involves proving properties of polymorphic functions. The new model supports straightforward validations of all the test equivalences that have been proposed in the literature for local-variable semantics, and encompasses standard methods of reasoning about data representations. It is not known whether our techniques yield fully abstract semantics. A model based on partial equivalence relations on the natural numbers is also brie y examined.

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confidence: 99%

Parametricity and Local Variables

O’Hearn¹,

Tennent²

1997

Algol-Like Languages

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“…Virtual classes provide an elegant solution to the extensibility problem [5,19]: how to easily extend a data abstraction with both new representations and new operations. This problem is also known as the expression problem because a canonical example is the representation of the abstract syntax of expressions [36,34,38].…”

Section: Higher-order Hierarchiesmentioning

confidence: 99%

A Virtual Class Calculus

Ernst¹,

Ostermann²,

Cook³

2005

DPB

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Virtual classes are class-valued attributes of objects. Like virtual methods, virtual classes are defined in an object's class and may be redefined within subclasses. They resemble inner classes, which are also defined within a class, but virtual classes are accessed through object instances, not as static components of a class. When used as types, virtual classes depend upon object identity -each object instance introduces a new family of virtual class types. Virtual classes support large-scale program composition techniques, including higher-order hierarchies and family polymorphism. The original definition of virtual classes in Beta left open the question of static type safety, since some type errors were not caught until runtime. Later the languages Caesar and gbeta have used a more strict static analysis in order to ensure static type safety. However, the existence of a sound, statically typed model for virtual classes has been a long-standing open question. This technical report presents a virtual class calculus, vc, that captures the essence of virtual classes in these full-fledged programming languages. The key contributions of the paper are a formalization of the dynamic and static semantics of vc and a proof of the soundness of vc.

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“…This is known as the Interpreter pattern 13]. 4 For instance, the SML program from Figs. 1 and 2 corresponds to the Java 1 4 ] program shown in Fig.…”

Section: The Object-oriented Approachmentioning

confidence: 99%

Synthesizing object-oriented and functional design to promote re-use

Krishnamurthi

Felleisen

Friedman

1998

ECOOP’98 — Object-Oriented Programming

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Many problems require recursively speci ed types of data and a collection of tools that operate on those data. Over time, these problems evolve so that the programmer must extend the toolkit or extend the types and adjust the existing tools accordingly. Ideally, this should be done without modifying existing code. Unfortunately, the prevailing program design strategies do not support both forms of extensibility: functional programming accommodates the addition of tools, while object-oriented programming supports either adding new tools or extending the data set, but not both. In this paper, we present a composite design pattern that synthesizes the best of both approaches and in the process resolves the tension between the two design strategies. We a l s o show h o w this protocol suggests a new set of linguistic facilities for languages that support class systems. Evolutionary Software DevelopmentProgramming practice frequently confronts programmers with the following design dilemma. A recursively de ned set of data must be processed by s e v eral di erent tools. In anticipation of future extensions, the data speci cation and the tools should therefore be implemented such that it is easy to 1. add a new variant of data and adjust the existing tools accordingly, a n d 2. extend the collection of tools. Ideally, these extensions should not require any c hanges to existing code. For one, source modi cation is cumbersome and error-prone. Second, the source may not be available for modi cation because the tools are distributed in the form of object code. Finally, i t m a y be necessary to evolve t h e b a s e This dilemma manifests itself in many di erent application areas. A particularly important example arises in the area of programming languages. Language grammars are typically speci ed via BNFs, which denote recursively de ned data sets. Language-processing tools recursively traverse sentences formed from the grammar. In this scenario, a new form of data means an additional clause in the BNF new tools must be able to traverse all possible elements of the (extended) grammar.Unfortunately, p r e v ailing design strategies do not accommodate the required evolution:The \functional" approach, which is often realized with conventional procedural languages, implements tools as procedures on recursive t ypes. While this strategy easily accommodates the extension of the set of tools, it requires signi cant source modi cations when the data set needs to be extended. The (standard) \object-oriented" approach de nes a recursive set of data with a collection of classes, one per variant (BNF clause), and places one method per tool in each c l a s s . I n the parlance of object-oriented design patterns 13], this approach i s k n o wn as the Interpreter pattern. The problem it poses is dual to the problem of the functional approach: variants are easy to add, while tool additions require code modi cations. If the collection of tools is large, the designer may also use the Visitor pattern, a variant o f t h e Interpreter...

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Object-oriented programming versus abstract data types

Cited by 68 publications

References 39 publications

Parametricity and Local Variables

Parametricity and Local Variables

A Virtual Class Calculus

Synthesizing object-oriented and functional design to promote re-use

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