Support for Metadata-driven Selection of Run-time Services in .NET is Promising but Immature

The .NET Framework allows developers to add run-time services to their classes by specifying them in metadata. This metadata-driven service selection is a very powerful and promising mechanism, closely related to ideas developed in the Aspect-Oriented Programming community. Interestingly, the .NET framework supports both services implemented by weaving and services implemented by interception. However, the weaving-based and the interception-based mechanisms seem to have been introduced in the framework independently, and show some unnecessary differences in flexibility, extensibility and configurability. Also both mechanisms still contain some anomalies in their design. In this paper, we describe the mechanisms, and discuss these shortcomings.