Adding Contracts to C++ with Transformers



Contract programming is a paradigm that allows developers to ensure that some conditions are satisfied when a function is called (preconditions), or when it returns (postconditions). It makes debugging easier and it is a good way to document what a function accepts as argument or ensures on the result. In oriented-object languages, it is also possible to check a set of conditions on every call and return of any member function of a class (class invariants), and conditions are inherited from parent classes. The Transformers project aims at providing source to source transformations on C and C++ sources. A C extension to support contracts in C has already been written, when C++ parsing wasn't working yet. We will show how to write a C++ grammar extension to bring contracts in the C++ with the Transformers project, and then how to transform this extended C++ into standard C++.