Because it solves nothing standard C++ style OO doesn't, and misses out on some of the good stuff that OO does.<p>Passing a map around in FP, and modifying it as it moves is virtually identical to adjusting a member_variable. Now however you can't protect the changes by having a setter.<p>After years in c and then c++ then rails and now elixir. I honestly don't see that there is a benefit to functional programming. My unit tests are the same, and the code is just as buggy regardless of approach.<p>It is never the OO vs FP that make the difference.