C++Now 2019

One of the largest and widest-reaching library design efforts undertaken by the ISO-C++ standard committee in recent years is the proposal of a generic abstraction for execution, known as an executor. Dating back to at least 2012, the effort to design an executors library for standard C++ has come to a head recently with its inclusion in the list of priorities for the C++20/23 timeframe. The effort to construct a concept-driven design that meets the needs of vastly different domains with vastly different approaches to execution and vastly different needs is one of the most ambitious generic programming exercises of its kind ever. In the past year in particular, the executors design effort has undergone significant changes to accommodate the needs of yet another domain and yet another perspective on execution. The authors of the proposals have had to invent new mechanisms for expressing the vast outer product of behaviors, semantics, performance hints, and other properties of executors in generic contexts.

While very few (if any) design efforts require the level of genericness and customizability that executor standardization demands, many of the lessons learned from the ongoing saga of executor design can be applied to any generic programming project. In addition to an update on the progress of ISO-C++ executors and a history of the design effort, this talk presents a discussion of the general principles of concept-driven design that can be extracted from the executors experience thus far. Additionally, this presentations goes into detail on the latest design iterations and outlook for executors, futures, and other concurrent programming abstractions in C++23 and beyond.