Refactoring in Ruby using dynamic methods and dynamic dispatch (1) using dynamic proxy that is also a blank slate (2) source: book - metaprogramming-ruby

refactoring_using_metaprogrammin.rb

# given class Computer: refactor me
class Computer
  def initialize(computer_id, data_source)
    @id = computer_id
    @data_source = data_source
  end

  def mouse
    info = @data_source.get_mouse_info(@id) 
    price = @data_source.get_mouse_price(@id) 
    result = "Mouse: #{info} ($#{price})"     
    return "* #{result}" if price >= 100 
    result
  end

  def cpu
    info = @data_source.get_cpu_info(@id) 
    price = @data_source.get_cpu_price(@id) 
    result = "Cpu: #{info} ($#{price})" 
    return "* #{result}" if price >= 100 
    result
  end
  
  def keyboard
    info = @data_source.get_keyboard_info(@id) 
    price = @data_source.get_keyboard_price(@id) 
    result = "Keyboard: #{info} ($#{price})" 
    return "* #{result}" if price >= 100
    result
  end

# ...
end


# refactoring: variant (1)
class Computer
  def initialize(computer_id, data_source)
    @id = computer_id
    @data_source = data_source
    data_source.methods.grep(/^get_(.*)_info$/) { Computer.define_component $1 }
  end

  def self.define_component(name) 
    define_method(name) do
      info = @data_source.send "get_#{name}_info", @id 
      price = @data_source.send "get_#{name}_price", @id 
      result = "#{name.capitalize}: #{info} ($#{price})" 
      return "* #{result}" if price >= 100
      result
    end 
  end
end


# refactoring: variant (2)
class Computer 
  instance_methods.each do |m|
    undef_method m unless m.to_s =~ /^__|method_missing|respond_to?/ 
  end

  def initialize(computer_id, data_source) 
    @id = computer_id
    @data_source = data_source
  end

  def method_missing(name, *args)
    super if !respond_to?(name)
    info = @data_source.send("get_#{name}_info", args[0]) 
    price = @data_source.send("get_#{name}_price", args[0]) 
    result = "#{name.to_s.capitalize}: #{info} ($#{price})" 
    return "* #{result}" if price >= 100
    result
  end

  def respond_to?(method) 
    @data_source.respond_to?("get_#{method}_info") || super
  end 
end