ruby - virtual proxy pattern

virtual_proxy.rb

class VirtualProxy < BasicObject
  def initialize(&loader)
    @loader = loader
    @object = nil
  end

  def method_missing(name, *args, &block)
    __load__
    @object.public_send(name, *args, &block)
  end

  def inspect
    "VirtualProxy(#{@object ? @object.inspect : ''})"
  end

  def __object__
    @object
  end

  def __load__
    @object ||= @loader.call
  end
end


#----------------------------------------------------------------------
# MODEL
#----------------------------------------------------------------------


class Car
  attr_accessor :name, :price, :wheels
  
  def initialize(name, price, wheels = nil)
    @name = name
    @price = price
    @wheels = wheels
  end
end


class Wheels
  attr_reader :brand

  def initialize(brand)
    @brand = brand
  end
end


#----------------------------------------------------------------------
# MAPPER
#----------------------------------------------------------------------


class CarMapper
  DATA_SRC = {
    3 => {
      :name => 'Ferrari',
      :price => 100_000,
      :wheels_id => 42,
    }
  }

  def wheels_mapper
    WheelsMapper.new
  end

  def find(id)
    data_src = DATA_SRC[id]
    car = Car.new(data_src[:name], data_src[:price])
    car.wheels = VirtualProxy.new {
      # reset wheels attribute, so that it type is correct
      car.wheels = wheels_mapper.find(data_src[:wheels_id])
    }

    car
  end
end


class WheelsMapper
  DATA_SRC = {
    42 => {
      :brand => 'Dunlop'
    }
  }

  def find(id)
    data_src = DATA_SRC[id]
    Wheels.new(data_src[:brand])
  end
end


def main
  car = CarMapper.new.find 3
  puts "name: #{car.name}", "price: #{car.price}$"
  puts car.wheels.inspect      # VirtualProxy()
  puts car.wheels.__object__   # nil
  puts car.wheels.brand        # 'Dunlop'
end

main()