COMPILING SCALA FOR THE JAVA VIRTUAL MACHINE - EPFL

Abstract
Scala is a new programming language developed at EPFL and incorporating
the most important concepts of object-oriented and functional languages.
It aims at integrating well with the Java and .NET platforms: their
respective libraries are accessible without glue code, and the compiler can
produce programs for both virtual machines.
This thesis focuses on the compilation of two important concepts of
Scala : mixin inheritance and run time types. The compilation techniques are
presented in the context of the Java virtual machine, but could be adapted
easily to other similar environments.
Mixin inheritance is a relatively recent form of inheritance, offering
new capabilities compared to single inheritance, without the complexity
of multiple inheritance. We propose two implementation techniques
for mixin inheritance: code copying and delegation. The implementation
used in the Scala compiler is then presented and justified.
Run time types make it possible for a program to examine the type of
its values during execution. This possibility is interesting in itself, offering
new capabilities to the programmer. Furthermore, run time types are
also required to implement other high level concepts, like pattern matching,
type-safe serialisation and reflection. We propose an implementation
technique based on the representation of types as values, and show how
to use the run time types of the underlying virtual machine to implement
those of Scala.
The techniques presented in this thesis have been implemented in our
Scala compiler, scalac. This enabled us to evaluate these techniques, in
particular their impact on the performances of programs. This evaluation
was performed on several real, non-trivial programs.