Emplace Enhancements for Maps and Unordered Maps

​With C++17 you get two new methods for maps and unordered maps:

• try_emplace() - if the object already exists, then it does nothing; otherwise,​ it behaves like emplace().

• emplace() might move from the input parameter when the key is in the map, that’s why it’s best to use find() before such emplacement.

• insert_or_assign() - ...