I personally don't know how it is implemented under the hood, but it is important to understand as a Ruby programmer that methods are not just functions. In fa

I personally don't know how it is implemented under the hood, but it is important to understand as a Ruby programmer that methods are not just functions. In fact functions are not really first class entities in Ruby. Instead you have a mishmash of procs, blocks, instance methods and class methods and they are all different to a certain degree. It's one of the big frustrations of programming in Ruby sometimes. But when it comes down to it what really is message passing? You have a reference to an object, a method name and a collection of parameters. When you dispatch the message you look for the method on the object and run the function passing in the parameters. Does it matter if you optimise the situation by placing the parameters on a stack and using a dictionary with a reference to the method? Or if you optimise by doing static analysis to look up the method and replace the dispatch with a direct call to the method? Or if you optimise further by inlining the code altogether? The point is not how it is implemented but how the programmer thinks of it. Object Oriented programming is a thing humans do, not a thing computers do. Object Oriented Programming Languages have features that make it more convenient to do Object Oriented programming. Whether the code is OO or not is only up to the programmer, not the compiler/interpreter. Having said all that, is Ruby my first choice for (what I understand to be) Alan Kay's model of OOP? No. But then I really don't know what my first choice would be. It is possible that the language hasn't been written yet ;-)