The Managed Adapter Pattern: Facilitating Glue Code Generation for Component Reuse

Abstract

The adapter or wrapper pattern is one of the most widely used patterns in software engineering since the problem of reconciling unsuitable component interfaces is so ubiquitous. However, the classic adapter pattern as described by the Gang of Four has some limitations which rule out its use in certain situations. Of the two forms of the pattern, only the object adapter form is usable with common programming languages not supporting multiple inheritance (such as Java or C#), and this is not able to adapt interfaces of classes whose own type is used in one or more of their operations. This makes it impossible for a tool to automatically generate “glue code” for such components and forces developers to come up with some non-trivial (and typically invasive) workarounds to enable clients to use them. In this paper we present an enhanced form of the adapter pattern which solves this problem by extending the way in which an adapter stores and manages adaptees. We therefore call it the Managed Adapter Pattern. After describing the pattern in the usual Gang of Four-oriented way, we describe its application in the system that initially motivated its development – a test-driven component search engine which is able to retrieve reusable assets based on their semantics. A key challenge in the implementation of this engine was developing a flexible glue code generator that was able to automate the creation of adapters for all the kinds of components delivered by the underlying component repository.