Improving application design with std::variant and templates

A std::variant can store a value of one type at a time, out of a user-defined set of types. Those types can be completely unrelated to one another, but we can design them to have similarities. Templates allow us to process unrelated types, if there is a common way to interact with them. Bring those two observations together, and wonderful things become possible.

In this talk, we explore combining template techniques with std::variant. The result? Extensible code with less boilerplate.

We cover the basics of the subject area, then start with a simple kind of lambda-based compile-time polymorphism. Using 'if constexpr' and C++20 concepts, we increase our options and flexibility. By exploring and visualizing both compile-time and a run-time aspects of our code, we understand some issues that may seem baffling at first, and then learn how to resolve them. All through the talk, we consider the impact on application design, and discuss possible tradeoffs.

After this talk, you will have a firm grasp on techniques that make std::variant even more useful in practice. This will give you more options for your next application subsystem design. You do not need prior knowledge of either std::variant or writing template code.