2019
https://pspdfkit.com/blog/2019/the-functional-side-of-optional/
2018
https://foonathan.net/blog/2018/12/11/nested-optionals-expected.html
https://blogs.msdn.microsoft.com/vcblog/2018/09/04/stdoptional-how-when-and-why/
https://www.bfilipek.com/2018/06/optional-examples-wall.html
https://www.bfilipek.com/2018/04/refactoring-with-c17-stdoptional.html
    https://habr.com/post/369811/
https://www.bfilipek.com/2018/05/errors-and-optional.html
https://www.bfilipek.com/2018/05/using-optional.html