Changed attributes

changed_attributes.rb

#
#  FIRST VERSION 
#
#  Using string interpolation
#
class Endpoint
  attr_reader :changed_attributes

  def self.has_attribute(attr_name)
    attr_reader attr_name
    class_eval %Q"
          def #{attr_name}=(value)
              unless defined? @changed_attributes
                  @changed_attributes = {}
              end
              @#{attr_name} = value
              @changed_attributes[:#{attr_name}] = value
          end
    "
  end
end

class Player < Endpoint
  has_attribute :nickname
  has_attribute :name

  def initialize(attributes = {})
    attributes.each do |k,v|
      send("#{k}=", v)
    end
  end
end

player = Player.new
player.nickname = 'mrnugget'

puts player.changed_attributes.inspect  # => {:nickname => "mrnugget"}


player2 = Player.new(name: 'Foobar')
puts player2.changed_attributes.inspect   # => {:name => "Foobar"}

player2.nickname = 'barfoobar'
puts player2.changed_attributes.inspect   # => {:name => "Foobar", :nickname => "barfoobar"}


#
#  SECOND VERSION 
#
#  Using `define_method`
#
#  Produces the same results
#
class Endpoint
  attr_reader :changed_attributes

  def self.has_attribute(attr_name)
    attr_reader attr_name
    class_eval do
      define_method("#{attr_name}=") do |value|
        unless defined? @changed_attributes
          @changed_attributes = {}
        end
        instance_variable_set("@#{attr_name}", value)
        @changed_attributes[attr_name] = value
      end
    end
  end
end

class Player < Endpoint
  has_attribute :nickname
  has_attribute :name

  def initialize(attributes = {})
    attributes.each do |k,v|
      send("#{k}=", v)
    end
  end
end