Encapsulation Constructs in Systems Programming Languages, 1984

This paper investigates the desirable properties of programming language constructs that support encapsulation of environments and abstract data types. These properties are illustrated by using a simple multiuser file system as a model. The requirements for such a file system are outlined; then the model file system design is described by a hierarchy of encapsulated abstract data types and environments. The high-level language constructs necessary to directly implement the model file system design are identified. It is concluded that environment encapsulation and abstract data types must be supported by different constructs, and the desirable properties of such constructs are outlined. A superset of Ada e that effectively supports both environments and abstract data types is introduced and used to implement the model file system. The encapsulation constructs of several modern systems programming languages are evaluated. Each of these languages is shown to be insufficient for a direct implementation of the model file system design.