Type systems built directly into the compiler or interpreter of a programming language cannot be easily extended to keep track of run-time invariants of new abstractions. Yet, programming with domain-specific abstractions could benefit from additional static checking. This paper presents library techniques for extending the type system of C++ to support domain-specific abstractions. The main contribution is a programmable “subtype” relation. As a demonstration of the techniques, we implement a type system for defining type qualifiers in C++, as well as a type system for the XML processing language, capable of, e.g., statically guaranteeing that a program only produces valid XML documents according to a given XML schema.
- Metaprogramming capabilities of C++ enable domain-specific type system extensions.
- A template library for building new type system extensions.
- Type system extensions for type qualifiers.
- Type system extensions for regular expression types for typing XML.
Keywords: Type systems; XML; Type qualifiers; C++; Template metaprogramming; Active libraries