Using Metadata Transformations to Integrate Class Extensions in an Existing Class Hierarchy

• Published in: Lecture notes in computer science pp. 290 - 306
• Main Author: Lumpe, Markus
• Format: Book Chapter Conference Proceeding
• Language: English
• Published: Berlin, Heidelberg Springer Berlin Heidelberg 2006; Springer
• Series: Lecture Notes in Computer Science
• Subjects: Applied sciences; Class Extension; Class Hierarchy; Class Point; Computer science; control theory; systems; Exact sciences and technology; Programming languages; Software; Text Section; Virtual Machine; Compilation; Programming language; Semantics; Programming environment; Virtual machine; Modular system; Inheritance; Unfolding; Metadata; Visibility; Integrity
• ISBN: 3540489371; 9783540489375
• ISSN: 0302-9743; 1611-3349
• DOI: 10.1007/11924661_18

Class extensions provide a fine-grained mechanism to define incremental modifications to class-based systems when standard subclassing mechanisms are inappropriate. To control the impact of class extensions, the concept of classboxes has emerged that defines a new module system to restrict the visibility of class extensions to selected clients. However, the existing implementations of the classbox concept rely either on a “classbox-aware” virtual machine, an expensive runtime introspection of the method call stack to build the structure of a classbox, or both. In this paper we present an implementation technique that allows for the structure of a classbox to be constructed at compile-time by means of metadata transformations to rewire the inheritance graph of refined classes. These metadata transformations are language-neutral and more importantly preserve both the semantics of the classbox concept and the integrity of the underlying deployment units. As a result, metadata transformation provides a feasible approach to incorporate the classbox concept into programming environments that use a virtual execution system.