double dispatch in ruby -> http://blog.bigbinary.com/2013/07/07/visitor-pattern-and-double-dispatch.html

double_dispatch.rb

class Node
  def accept visitor
		raise NotImplementedError.new
	end
end

module Visitable
	def accept visitor
		visitor.visit self
	end
end

class IntegerNode < Node
	include Visitable

	attr_reader :value

	def initialize(value)
		@value = value
	end
end

class StringNode < Node
	include Visitable

	attr_reader :value

	def initialize(value)
		@value = value
	end
end


class Ast < Node
	def initialize
		@nodes = []
		@nodes << IntegerNode.new(2)
		@nodes << IntegerNode.new(3)
	end

	def accept visitor
		@nodes.each do |node|
			node.accept visitor
		end
	end
end

class BaseVisitor
	def visit subject
		method_name = "visit_#{subject.class}"
		send(method_name, subject)
	end
end

class DoublerVisitor < BaseVisitor
	def visit_IntegerNode(subject)
		puts subject.value * 2
	end

	def visit_StringNode(subject)
		puts subject.value.to_i * 2
	end
end

Ast.new.accept(DoublerVisitor.new)