Objects as closures: abstract semantics of object-oriented languages

Abstract

We discuss denotational semantics of object-oriented languages, using the concept of closure widely used in (semi) functional programming to encapsulate side effects. It is shown that this denotational framework is adequate to explain classes, instantiation, and inheritance in the style of Sirnula as well as SMALLTALK-80. This framework is then compared with that of Kamin, in his recent denotational definition of SMALLTALK-80, and the implications of the differences between the two approaches are discussed.

Object-oriented programming versus abstract data types

“…As combinations of procedural observations with shared local state, PDAs are naturally implemented as closures containing records of procedures [37]. The procedures are derived from the specification of the data abstraction.…”

“…In this tutorial, Smalltalk is taken as the paradigmatic object-oriented language. A useful theory of objects associates them with some form of closure [2,37,8], although other models are possible [26]. The term "object" is not very descriptive of the use of collections of procedures to implement a data abstraction.…”

Digital Object Prototypes: An Effective Realization of Digital Object Types

“…Our approach draws on the notions of the OO paradigm, due to its well established foundations and its well known concepts. Approaches on the formalization of OO semantics [2,12] show that the notion of objects in OO languages and the notion of digital objects in a DL system present significant similarities, yet in a different level of abstraction. [1] defines OO systems in terms of the following requirements:…”

Static Typing for Object-Oriented Programming

“…A formal proof of these claims should be based on a dynamic semantics of the example language [47,31]. We will not go into the details in this paper, however, but move on to define a convenient representation of classes.…”

“…It has been argued by Snyder [52] that much better encapsulation is achieved if only the existing methods can be referred; we ignore this consideration in this paper. For a denotational semantics of inheritance, see [17,47,31,14].…”