Pattern-based Traits

There have been exciting developments with respect to compile-time reflection for C # and Java. Fähndrich et al. [2006] introduced what we call pattern-based reflection as a high-level notation for inspecting members of old classes and generating members of a new class. Huang and Smaragdakis [2008, 2011] further increased the expressiveness of pattern-based reflection and strengthened its type safety guarantees. However, these proposals took place in settings with just classes and/or mixins, which limit the ways that generated declarations can be composed (just linearly). In this paper we investigate the combination of pattern-based re-flection with traits, which offer more expressive forms of composi-tion. Further, we provide language features for manipulating sets of member declarations: giving them names, manipulating their domains using set operations, and passing them as arguments to traits. To demonstrate the expressiveness of the proposed language design, we implement a library for object-relational mapping. We also formalize the language design, defining the syntax and seman-tics for a language named PTFJ (for Pattern-based Traits in Feath-erweight Java