Aliasing to an inherited method

ruby-talk
1

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?

2

#new is a class method so you got to get up in that class level.

  class Class
    class << self
      alias_method :__new__, :new
    end
  end

3

Okay, so put the class-level where it beleongs:

      puts "Is __new__ available? #{method( :__new__ )}"
      class << self
        alias_method :new, :__new__
      end

T.

4

Trans wrote:

#new is a class method so you got to get up in that class level.

  class Class
    class << self
      alias_method :__new__, :new
    end
  end

Actually, the instance methods defined in Class become class methods in every instance of it (classes)

   class Class
     def foo; "bar; end
   end

   Integer.foo => "bar"

It's a bit confusing, but just think of every class in Ruby as an instance of Class.

Cheers,
Daniel

5

Oops, my bad. You're right Daniel. I didn't even notice that was class
Class.