C++Now 2021

C++20 concepts give us a brand new way to specify how our generic libraries and algorithms should be used and allow library users to better understand what is expected of them. However, concepts didn't rise from chaos, and before their adoption C++ library authors had other mechanisms to meet that goal.

In this talk I'll briefly discuss concepts, describe a variety of more mature methods for libraries to constrain and tailor their interaction with application code. Mechanisms such as tag-dispatch, specializations and customization points will be compared to concepts and to each other, and usage tips will be presented.

Special attention will be given to the 'semantic' vs. 'syntactic' nature of concepts. I'll show potential pitfalls and 'famous' cases where semantics played a significant role, and present the case for some 'semantic only' concepts, and suggest how they can be used to improve library APIs.