Load-Time Adaptation: Efficient and Non-Intrusive Language Extension for Virtual Machines

The advantages of virtual machine (VM) execution (dynamically loaded, portable object files with high-level information) also permit changing the semantics of executables. Load-time adaptation (LTA) intercepts the VM''s file operations and modifies object code on the fly, without changing the VM implementation, without needing access to source code, and without changing the actual files. We introduce a new technique, library-based LTA, and show how it can extend languages in such ways as adding contracts or mixins to existing classes, providing default code for interfaces, and instantiating parameterized types. We discuss an implementation of library-based LTA and its application to extending Java semantics.