multi_defs.rb

require 'pry'
module DefineMulti
  def method_missing(original_caller, *args)
    the_method = "_#{args.length}_#{original_caller}".to_sym
    unless self.methods.include?(the_method)
      raise NoMethodError, "Undefined method '#{original_caller}' with arity #{args.size}"
    end
    public_send(the_method, *args)
  end

  def self.included(base)
    base.extend(ClassMethods)
  end

  module ClassMethods
    def method_added(the_method)
      @overloaded_methods ||= Hash.new{|k,v| k[v] = []}
      return if @overloaded_methods.values.flatten.include?(the_method)

      method_obj = instance_method(the_method)
      arity = method_obj.arity
      new_method_name = "_#{arity}_#{the_method}".to_sym
      @overloaded_methods[the_method] << new_method_name
      alias_method new_method_name, the_method
      undef_method the_method
    end

    def define_multi(&block)
      class_eval(&block)
    end
  end
end

class MultiClass
  include DefineMulti
  define_multi do
    def multiple_heads(arg)
      puts "One Arg"
    end

    def multiple_heads(arg1, arg2)
      puts "Two Args"
    end
  end
end

MultiClass.new.multiple_heads("beef")
MultiClass.new.multiple_heads("beef", "ham")
MultiClass.new.multiple_heads("beef", "ham", "chicken")