https://www.boost.org/doc/libs/develop/libs/outcome/doc/html/index.html
https://github.com/boostorg/outcome

https://ned14.github.io/outcome/
https://github.com/ned14/outcome
https://github.com/ned14/boost-outcome

2019
https://www.reddit.com/r/cpp/comments/aqidl6/boostoutcome_ready_for_boost_170_release/