the-abstract-factory-pattern

The Abstract Factory Pattern

1. An object dedicated to creating a compatible set of objects is called an abstract factory

class PondOrganismFactory
  def new_animal(name)
    Frog.new(name)
  end

  def new_plant(name)
    Algae.new(name)
  end
end

class JungleOrganismFactory
  def new_animal(name)
    Tiger.new(name)
  end

  def new_plant(name)
    Tree.new(name)
  end
end

class Habitat
  def initialize(number_animals, number_plants, organism_factory)
    @organism_factory = organism_factory

    @animals = []
    number_animals.times do |i|
      animal = organism_factory.new_animal("Animal#{ i }")
      @animals << animal
    end

    @plants = []
    number_plants.times do |i|
      plant = organism_factory.new_plant("Plant#{ i }")
      @plants << plant
    end
  end
end

jungle = Habitat.new(1, 4, JungleOrganismFactory.new)
jungle.simulate_one_day

pond = Habitat.new(2, 4, PondOrganismFactory.new)
pond.simulate_one_day

Store Class in instance variables

class OrganismFactory
  def initialize(plant_class, animal_class)
    @plant_class = plant_class
    @animal_class = animal_class
  end

  def new_animal(name)
    @animal_class.new(name)
  end

  def new_plant(name)
    @plant_class.new(name)
  end
end

jungle_organism_factory = OrganismFactory.new(Tree, Tiger)
pond_organism_factory = OrganismFactory.new(WaterLily, Frog)

jungle = Habitat.new(1, 4, jungle_organism_factory)
jungle.simulate_one_day

pond = Habitat.new(2, 4, pond_organism_factory)
pond.simulate_one_day

Leveraging the name

class IOFactory
  def initialize(format)
    @reader_class = self.class.const_get("#{ format }Reader")
    @writer_class = self.class.const_get("#{ format }Writer")
  end

  def new_reader
    @reader_class.new
  end

  def new_writer
    @writer_class.new
  end
end

html_factory = IOFactory.new('HTML')
html_reader = html_factory.new_reader

pdf_factory = IOFactory.new('PDF')
pdf_writer = pdf_factory.new_writer