The full video from CppCon is available here: https://www.youtube.com/watch?v=PVYdHDm0q6Y
C++ provides a much richer set of abstractions than C. Classes, templates, overloading, and other core C++ features can be leveraged for more readable syntax, better compile time typechecking, more open ended genericity and improved modularity. On the flip side, C89 still boasts some advantages over C++, especially when viewed through a pragmatic lens. C ABIs on many platforms have been stable for decades, practically every language supports binding to C code through foreign function interfaces, and including nearly any C89 header has a negligible effect on compile time on modern computers.
The hourglass pattern provides the best of both worlds. By placing a headers-only C++ interface on top of a minimal C89 interface, it makes ABI issues a non-concern, and enables just a single binary to be shipped for a given platform. It makes providing bindings from other languages easier, and prevents ABI issues like incompatibilities between debug and release variants of runtimes.
This talk provides an overview of the pattern and teaches practical techniques for its implementation using C++14. Real shipping projects inspired the best practices described in the slides.
Code corresponding to this presentation can be found here: https://github.com/CppCon/CppCon2014/tree/master/Presentations/Hourglass%20Interfaces%20for%20C%2B%2B%20APIs%20-%20Stefanus%20Du%20Toit%20-%20CppCon%202014/code