CppCon 2024

For many years, members of the C++ working group, WG21, have tried to add support for contract assertions — preconditions, postconditions, and assertion statements within a function body — to the C++ language. It’s been a long and difficult road, but we now have a proposal (P2900, “Contracts for C++”) to add significant contract support in, we hope, C++26, with more complete support to follow in C++29.

Looking back, the contracts feature has been unusually difficult and contentious. I contend that the difficulty is inherent in the feature: a contracts facility, by its nature,  cannot be understood from any single point of view.

In this lecture, I will explain why understanding contracts requires seeing the feature from a panoply of perspectives, and show how shifting between these perspectives allows one to make effective use of the facility.

This lecture is derived from presentations made to the Language Evolution subgroup of WG21 at the St. Louis meeting in June 2024.