From: Phrogz <gavin@...>
Date: 2005-12-02T08:27:31+09:00
Subject: Aliasing to an inherited method

I tried to modify Daniel Schierbeck's code (in response to the recent
"abstract class" thread) to not have an additional method dispatch.
This line here:

  def self.new(*args, &block)
    __new__(*args, &block)
  end

cries out for a direct alias, to me. Unfortunately, what I hoped would
work didn't. It looks like #alias_method only looks for methods on the
current class; it's not able to alias to a method from an ancestor
class.

class Class
  alias_method :__new__, :new
end

module NonInstantiable
  def self.included(klass)
    super
    klass.module_eval {
      def self.inherited( subklass )
        subklass.module_eval {
          puts "Is __new__ available? #{method( :__new__ )}"
          alias_method :new, :__new__
        }
      end
    }
  end
end

class BaseKlass
  include NonInstantiable
end

class SubKlass < BaseKlass; end

p SubKlass.new
p BaseKlass.new

#=> Is __new__ available? #<Method: Class#__new__>
#=> tmp.rb:12:in `alias_method': undefined method `__new__' for class
`SubKlass' (NameError)


Is this behavior desirable, a necessary evil, or an oversight?