value_object.rb

class ValueObject
  NotImplementedInSubclassError = Class.new(StandardError)
  
  def initialize
    raise NotImplementedInSubclassError, 'Value Objects must implement a constructor'
  end
  
  # This is not ideal, since it will fail if the object contains any instance variables that are not exposed via getter methods.
  def ==(other)
    return false unless self.class == other.class
    self.instance_variables.map do |iv|
      method_name = iv.to_s[1..-1].to_sym
      return false if self.send(method_name) != other.send(method_name)
    end
    true
  end
  alias :eql? :==

  def hash
    self.instance_variables.map {|iv| self.instance_variable_get(iv)}.hash
  end
end