> That's not true, you can always have a "send_message(string id)". Few people do it because you lose static type safety. And some languages, like C# and Scala, have dynamic types that allows for the "method_missing" protocol and such features are very unpopular.

That is the difference. If every class in C++ had only one method - send_message and each object is an independent thread, you will get how Erlang works. That is how you would do the actor model in C++.

Inheritance, Polymorphism is emphasised in Java, C++ and C#, whereas Functional programmers emphasise function objects / lambdas / Command Pattern where you just have one method - calling the function. Infact having just method you no longer need Polymorphism / Interfaces.