Metaprogramming ruby example

metaprogramming_ruby_ex.rb

# We create a container class. We only store the product's name at instantiation
class Container

  attr :product_name

  def initialize(name)
    @product_name = name
  end

end

# Apples ! Oranges ! All of theses fruits are contained in FruitContainer extending Container
# For simplification we only have one scanner
class FruitContainer < Container

  def apples_scanner
    puts "Scanning apples..."
  end

end

# Potatoes ! Broccoli ! All of vegetables are contained in VegetableContainer extending Container
# For simplification we only have one scanner
class VegetableContainer < Container

  def potatoes_scanner
    puts "Scanning potatoes..."
  end

end

# The Cargo containing all the containers
class Cargo

  # The constructor accepting multiple parameters
  def initialize(*containers)
    containers.each do |container|
      # self.class.send is used to define singleton methods for our class
      # we could also use define_singleton_method
      self.class.send(:define_method, "inspect_#{container.product_name}") do
        scanner_name = "#{container.product_name}_scanner"
        if container.respond_to?(scanner_name)
          container.send(scanner_name)
        else
          puts "No scanner found."
        end
      end
    end
  end

end

potatoes_container = VegetableContainer.new "potatoes"
apples_container = FruitContainer.new "apples"
cargo = Cargo.new(potatoes_container, apples_container)

cargo.inspect_apples
cargo.inspect_potatoes