CppCon 2026

C++26 reflection was designed so that it could open doors that have been shut since the creation of the language. One of the most firmly bolted doors — type erasure — can be broken down by pushing our new code generation capabilities to their limit. Introducing duck, an open-source library built to harness this new power.

So far, reflection gives us just one function to generate code: define aggregate, which lets you build a simple type. duck uses define aggregate to generate a vtable, transforming a tool for building simple types into one that builds interfaces. You declare an interface as an ordinary struct of C++ function declarations. Plug any type that already has those functions into duck, and you can dynamically call it with plain duck.quack() syntax — no inheritance, adapters, or macros required. This means you can avoid handwriting simply to connect other pieces of code. State what a capability means, and everything you already own that does it is compatible — your types, a vendor's, generated ones, a fifteen-year-old module nobody wants to reopen.

Through this talk, you will learn the basics of code generation with reflection, grounded entirely in real stories from duck's implementation. We'll look at where existing approaches struggle, how duck solves these historic problems, and the central technique: using define_aggregate to both synthesize a vtable and simulate member function call syntax.

We'll end by looking at the future of type erasure: the C++29 proposal for std::protocol, how token injection can perfect the implementation of duck, and how you can help push the frontier of reflection.