Wolfgang Bangerth

Wolfgang Bangerth

Mathematical software has traditionally been built in the form of "packages" that build on each other. A substantial fraction of these packages is written in C++ and, as a consequence, the interface of a package is described in the form of header files that downstream packages and applications can then #include. C++ has inherited this approach towards exporting interfaces from C, but the approach is clunky, unreliable, and slow. As a consequence, C++20 has introduced a "module" system in which packages explicitly export declarations and code that compilers then store in machine-readable form and that downstream users can "import" -- a system in line with what many other programming languages have used for decades. Herein, I explore how one can convert large mathematical software packages written in C++ to this system, using the deal.II finite element library with its around 800,000 lines of code as an example. I describe an approach that allows providing both header-based and module-based interfaces from the same code base, discuss the challenges one encounters, and how modules actually work in practice in a variety of technical and human metrics. The results show that with a non-trivial, but also not prohibitive effort, the conversion to modules is possible, resulting in a reduction in compile time for the converted library itself; on the other hand, for downstream projects, compile times show no clear trend. I end with thoughts about long-term strategies for converting the entire ecosystem of mathematical software over the coming years or decades.

Daniel S. Katz, Kyle E. Niemeyer, Sandra Gesing et al.

This report records and discusses the Fourth Workshop on Sustainable Software for Science: Practice and Experiences (WSSSPE4). The report includes a description of the keynote presentation of the workshop, the mission and vision statements that were drafted at the workshop and finalized shortly after it, a set of idea papers, position papers, experience papers, demos, and lightning talks, and a panel discussion. The main part of the report covers the set of working groups that formed during the meeting, and for each, discusses the participants, the objective and goal, and how the objective can be reached, along with contact information for readers who may want to join the group. Finally, we present results from a survey of the workshop attendees.