From: Trans <transfire@...>
Date: 2007-02-18T10:24:37+09:00
Subject: More flexible inheritance

A notion came to me yesterday with regards to how we extend classes.
On the one hand we can create a module and include it into a class,
but this will not allow us to override a preexisting method -- for
that we must reopen the class and play the alias and/ or binding game.
Various ideas have been put forth for simplifying and improving the
robustness of this, from #wrap_method, alias_method_chain, as well
as :pre, :post methods and my own cuts (albeit they go a bit further
than just method wrapping). But occurs to me that these add
complexities onto something that is already straightforward if we are
willing to separate out all class concerns into modules. In other
words instead of writing:

  class X
    def a; "a";  end
  end

write:

  module Xa
    def a; "a";  end
  end

  class X
    include Xa
  end

  X.new.a  #=> "a"

Then it's easy enough to overlay new behaviors:

  module Xb
    def a; "{"+super+"}";  end
  end

  class X
    include Xb
  end

  X.new.a  #=> "{a}"

Since that works so well, it occurs to me, why not make this the
fundamental behavior of defining a class? In other words defining a
class:

  class X
    def a; "a"; end
  end

could be equivalent to writing:

  class X
    include( Module.new{
        def a; "a";  end
    } )
  end

So there would always be a module involved in the definition of a
class. And classes become simply containers of modules.

T.