CppCon 2019

Modules are merged into the C++20 draft which means we now have a good idea what to expect, functionality-wise. Tooling support is also not far behind with compiler and build system vendors making steady progress. So we've got modules, but what now? How do we start using modules in our projects?

The aim of this talk is to answer the "What (& Why)", "How", and "When" of C++ Modules: what are modules (& why do we need them), how to apply them to new and existing codebases, as well as when can we start the migration.

We begin with a brief introduction to modules (structure, partitions, header units, include translation) and their relation to other physical design mechanisms (namespaces, headers, libraries, packages). We will also get a basic understanding of the underlying build mechanics which turns out to be necessary to use modules effectively.

Next we dive into the practical aspects of using modules: should we start with header units or go straight to proper modules? If header units, then should we use explicit import or rely on include translation? And if proper modules, then what is the appropriate module granularity? How to name our modules? Split or not to split (into module interface/implementation units)? And what about module distribution?

We conclude the talk by discussing the state of compilers, build systems, and (system) headers with regard to modules and whether now is a good time to start a new or modularize an existing project.