Why is there no std::future::then in C++17?

Question

boost::future has a member function: boost::future::then, while std::future has no std::future::then.

This wonderful article shows how useful std::future::then would be.

Why is there no std::future::then in C++17?

Is it just an oversight, or because of other rationale behind?

Answer 1

.then support was incorporated into the Concurrency TS, which was finalized in early 2016. There was little practical experience with implementations of Concurrency TS, and with little time remaining until C++17 needed to be feature complete, it didn't make it in. Indeed, it was so late they didn't even bother proposing to add it to C++17.