Iterator Traits (7.5), traits, std::iterator<>

http://en.cppreference.com/w/cpp/iterator

2019
https://www.fluentcpp.com/2019/04/16/an-alternative-design-to-iterators-and-ranges-using-stdoptional/
2018
https://infektor.net/posts/2018-11-03-iterators-what-must-be-done.html
https://github.com/codereport/Cplusplus/blob/master/Iterators.cpp
https://www.youtube.com/watch?v=yTi46Pb32qg