Metadata-driven library design

Library development has greatly benefited form the wide adop- tion of virtual machines like Java and Microsoft .NET. Reflection services and first class dynamic loading have contributed to this trend. Microsoft introduced the notion of custom annotation, which is a way for the programmer to define custom metadata stored along reflection meta-data within the executable file. Re- cently, Java also has introduced an equivalent notion into the virtual machine. Custom annotations allow the programmer to give hints to libraries about his intention without having to intro- duce semantic dependencies within the program; on the other hand these annotations are read at runtime introducing a certain amount of overhead. The aim of this paper is to investigate the impact of this new feature on library design, focusing both on expressivity and performance issues