It is also available in Eiffel, OCaml and Python.

So there are some good ways to make use of it.

But I agree interfaces/traits is a better way of dealing with multiple inheritance scenario.

> Didn't we learn from C++ that multiple inheritance is good in theory but in practice a horrible idea?

No, we learned from C++ that C++ multiple inheritance is an atrocity. Python's MI works in a clear and obvious way, similar[0] to how the Ruby inheritance chain is clear and obvious. MI really doesn't fit Ruby though, and IMHO would look too bolted on.

Most of the time the problem is people beating the platform they develop on into submission, instead of embracing it by getting a clear picture of what happens.

[0] As _why said[1], python and ruby are damn close: you can easily get something similar to Ruby's modules and inject them dynamically in the inheritance chain: https://gist.github.com/3951273

[1] https://github.com/whymirror/unholy

Magic is bad, but multiple inheritance isn't magic; it's clear and obvious, the only potential wrinkle being method resolution order when two superclasses define the same method, which is fine as long as it's consistent and documented.

Almost all of the problems with multiple inheritance in C++ are to do with the static type of an instance, and go away in a language where everything is virtual by default, as in ruby.