オブジェクト指向設計実践ガイドから学ぶ再利用性の高い設計について

# 『オブジェクト指向設計実践ガイド』p41より
class Gear
  attr_reader :chainring, :cog, :rim, :tire
  def initialize(chainring, cog, rim, tire)
    @chainring = chainring
    @cog = cog
    @rim = rim
    @tire = tire # ギアのクラスにタイアのサイズの属性が存在するのはおかしい
  end
  ...

  # ギアインチ = ギア比 * 車輪の直径
  # ギア比の計算と車輪の直径それぞれの計算も担っている
  def gear_inches
    chainring / cog.to_f * (rim + (tire * 2))
  end
end

# 『オブジェクト指向設計実践ガイド』p56より
class Gear
  attr_reader :chainring, :cog, :wheel
  def initialize(chainring, cog, wheel)
    @chainrign = chainring
    @cog = cog
    @wheel = wheel
  end

  def gear_inches
    ratio * wheel.diameter
  end

  def raito
    chainring / cog.to_f
  end
  ...
end

class Wheel
  attr_reader :rim, :tire
  def initialize(rim, tire)
    @rim = rim
    @tire = tire
  end
  ...

  def diameter
    rim + (tire * 2)
  end
end

# 『オブジェクト指向設計実践ガイド』p46より
class Gear
  attr_reader :chainring, :cog, :rim, :tire
  def initialize(chainring, cog, rim, tire)
    @chainrign = chainring
    @cog = cog
    @rim = rim
    @tire = tire
  end

  # 一漕ぎあたりの回転数
  # 計算ロジックを他の箇所から分離する
  def ratio
    @chainring / @cog.to_f
  end
end

# 『オブジェクト指向設計実践ガイド』p50より
class Wheel
  attr_reader :data
  def initialize(data)
    @data = data
  end

  def diameters
    data.collect do |cell|
      cell[0] + (cell[1] * 2)
    end
  end
end

@data = [[622, 20], [622, 23], [599, 30], [559, 40]]
Wheel.new(data).diameters

# 『オブジェクト指向設計実践ガイド』p50より
class Wheel
  attr_reader :wheels
  def initialize(data)
    @wheels = wheelify(data)
  end

  def diameters
    wheels.map {|wheel| wheel.rim + (wheel.tire * 2) }
  end

  private

  Wheel = Struct.new(:rim, :tire)
  def wheelify(data)
    data.map {|cell| Wheel.new(cell[0], cell[1]) }
  end
end

# 『オブジェクト指向設計実践ガイド』p56より
class Gear
  attr_reader :chainring, :cog, :rim, :tire
  def initialize(chainring, cog, rim, tire)
    @chainrign = chainring
    @cog = cog
    @rim = rim
    @tire = tire
  end

  def ratio
    chainring / cog.to_f
  end

  def gear_inches
    ratio * Wheel.new(rim, tire).diameter
  end
end

class Wheel
  attr_reader :rim, :tire
  def initialize(rim, tire)
    @rim = rim
    @tire = tire
  end

  def diameters
    rim + (tire * 2)
  end
end

class Gear
  attr_reader :chainring, :cog, :wheel
  def initialize(args)
    @chainring = args[:chainring]
    @cog = args[:cog]
    @wheel = args[:wheel] # DI: 初期化時の引数にインスタンスを渡す
  end

  def gear_inches
    ratio * wheel.diameter # diameterというパブリックインターフェースに依存する
  end
end

Gear.new(52, 11, Wheel.new(26, 1.5)).gear_inches

class Wheel
  def initialize(rim, tire)
    @rim = rim
    @tire = tire
  end

  def diameter
    ...
  end
end

# 『オブジェクト指向設計実践ガイド』p１２６より
class Trip
  attr_reader :bicycles, :customers, :vehicle
  def prepare(preparers)
    preparers.each do |preparer|
      case preparer
      when Mechanic
        preparer.prepare_bicycles(bicycles)
      when TripCoordinator
        preparer.buy_food(customers)
      when Driver
        preparer.fill_water_tank(vehicle)
      end
    end
  end
end

class Mechanic
  def prepare_bicycles(bicycles)
  end
end

class TripCoordinator
  def buy_food(customers)
  end
end

class Driver
  def fill_water_tank(vehicle)
  end
end

# 『オブジェクト指向設計実践ガイド』p１２7より
class Trip
  attr_reader :bicycles, :customers, :vehicle
  def prepare(preparers)
    preparers.each do |preparer|
      preparer.prepare_trip(self)
    end
  end
end

class Mechanic
  def prepare_trip(trip)
    trip.bicycles.each do |bicycle|
      prepare_bicycle(bicycle)
    end
  end
end

class TripCoordinator
  def prepare_trip(trip)
    buy_food(trip.customer)
  end
end

class Driver
  def prepare_trip(trip)
    fill_water_tank(trip.vehicle)
  end
end

# 『オブジェクト指向設計実践ガイド』p１45より
class Bicycle
  attr_reader :style, :size, :tape_color, :front_shock, :rear_shock

  def initialize(args)
    @style = args[:style]
    @size = args[:size]
    @tape_color = args[:tape_color]
    @front_shock = args[:front_shock]
    @rear_shock = args[:rear_shock]
  end

  def spares
    if style == :road
      {
        chain: '10-speed',
        tire_size: '23',
        tape_color: tape_color
      }
    else
      {
        chain: '10-speed',
        tire_size: '2.1',
        rear_shock: rear_shock
      }
    end
  end
end

# 『オブジェクト指向設計実践ガイド』p１75より
class Bicycle
  attr_reader :size, :chain, :tire_size

  def initialize(args={})
    @size = args[:size]
    @chain = args[:chain]
    @tire_size = args[:tire_size]
    post_initialize(args)
  end

  def spares
    {
      tire_size: tire_size,
      chain: chain
     }.merge(local_spares)
  end

  # subclass may override
  def post_initialize(args)
    nil
  end

  def local_spares
    {}
  end
end

class RoadBike < Bicycle
  attr_reader :tape_color
  def post_initialize(args)
    @tape_color = args[:tape_color]
  end

  def local_spares
    {tape_color: tape_color}
  end
end

class MountainBike < Bicycle
  attr_reader :front_shock, :rear_shock
  def post_initialize(args)
    @front_shock = args[:front_shock]
    @rear_shock = args[:rear_shock]
  end

  def local_spares
    {rear_shock: rear_shock}
  end
end