Towards a Java Library to Support Runtime Metaprogramming

Statically typed languages such as Java offer two key advantages: robustness increase due to compile time error detection, and better runtime performance caused by the reduction of runtime type checking. However, dynamic languages are sometimes preferred in scenarios where runtime adaptability is a strong requirement, such as building software capable of adapting to runtime changing environments. The metaprogramming features of dynamic languages allow the runtime adaptation of class and object structures, modifying inheritance relationships, and the evaluation of dynamically generated code. In this position paper, we describe the steps we are following to add to Java some of the metaprogramming services provided by most dynamic languages. The objective is to provide the runtime flexibility of structural intercession, dynamic inheritance and dynamic code evaluation, without losing the robustness of compile-time type checking. The metaprogramming services are provided as a library so, unlike other existing systems, any standard virtual machine and language implementation could be used.