From: Marc Heiler <lists@...>
Date: 2012-11-06T02:44:18+09:00
Subject: Re: Support for multiple Inheritance by classes

> If you really want a Ruby-like language with multiple
> inheritance, might I suggest Python?

What I do not understand is why people suggest other languages.

It is not as simple. Python uses so many different ways,
it has a completely different philosophy, so suggesting to
use another language A because you do not like one component
in language B isn't any real improvement.

Via modules in ruby you can get quite close to what multiple
inheritance solves.

There is no need to go to python at all.

Ruby and Python are way too similar in their ecological
niche as well.

There is one thing that is however not looked at much at
all in this discussion - less the distinction between
multiple inheritance vs. module mixins, and much more so
what the distinction class vs. module actually serves.

Because I often feel that the distinction between classes
and modules is much more arbitrary than seems to be reasonable.

You have a class Foo, and you mixin three different modules
into it. That is quite close to what multiple inheritance
does too, just not following the classical subclassing tree.

But why is that behaviour contained within a module? Why
could we not assume that ALL behaviour of every object
resides in an (perhaps invisible) module?

Then we could use classes the same way as modules.

module Foo
end

module Bar
  include Foo
end

vs.

class Foo
end

class Bar < Foo
end

To me this is a distinction in Ruby that I do not really
feel is compelling at all.

I have seen people use

class Foo
  module Bar
  end
end

And I asked them why they did it that way, and they told
me that the toplevel class gives them more features,
namely the ability to do Foo.new, than it would by
using a module. That baffled me when I heard it.

My question thus is:

Why must there be this distinction between classes and
modules in this way?

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