Flexible dynamic linking

Portability of programs between run-time environments is regarded as a desirable feature by programmers and users. In a modern virtual machine like the JVM, portability is supported by large standard libraries. A program that uses an interface from a standard library should be portable to any run-time environment that provides an implementation of the interface. Because different implementations of an interface have different names, a programmer who desires portability must write code to select an implementation. This introduces software engineering costs and type-safety concerns. We believe that dynamic linking is well-suited to providing portability automatically. Link-ing traditionally requires that types from the compile-time environment are present in the run-time environment. We suggest “flexible ” dynamic linking that relaxes a program’s depen-dencies on compile-time types in a type-safe and language-independent way, thus providing portability to different run-time environments. Bytecode is annotated with type variables rather than type names, and a non-deterministic model substitutes type variables with type names during linking. We interleave linking with execution, as in the JVM, and examin