Ruby中的工厂方法

如果我创建了一个未被调用的工厂方法 new 或 initialize ,我想这并不能真正回答“我如何制作一个…构造函数…”的问题,但我认为我会这样做。。。

class Vehicle
  def Vehicle.factory vt
    { :Bike => Bike, :Car => Car }[vt].new
  end
end

class Bike < Vehicle
end

class Car < Vehicle
end

c = Vehicle.factory :Car
c.class.factory :Bike

^{工厂 在这个教学示例中效果很好,但您可能需要考虑IRL @AlexChaffee 评论中的建议。}

class Vehicle
  VEHICLES = {}

  def self.register_vehicle name
    VEHICLES[name] = self
  end

  def self.vehicle_from_name name
    VEHICLES[name].new
  end
end

class Bike < Vehicle
  register_vehicle 'mountain bike'
end

class Car < Vehicle
  register_vehicle 'ferrari'
end

我喜欢类的标签与类本身一起保存,而不是将关于子类的信息与超类一起存储。未调用构造函数 new

> Vehicle.vehicle_from_name 'ferrari'
=> #<Car:0x7f5780840448>
> Vehicle.vehicle_from_name 'mountain bike'
=> #<Bike:0x7f5780839198>

请注意 某物 需要确保在运行vehicle_from_name之前加载了这些子类(可能这三个类位于不同的源文件中),否则超类将无法知道存在哪些子类,也就是说,在运行构造函数时,您不能依赖自动加载来拉入这些类。

我通过将所有子类放入例如a中来解决这个问题 vehicles 子目录并将其添加到末尾 vehicle.rb :

require 'require_all'
require_rel 'vehicles'

使用 require_all https://rubygems.org/gems/require_all 和 https://github.com/jarmo/require_all )

改编自 here ,我有

class Vehicle
  def self.new(model_name)
    if model_name == 'mountain bike'  # etc.
      object = Bike.allocate
    else
      object = Car.allocate
    end
    object.send :initialize, model_name
    object
  end
end

class Bike < Vehicle
  def initialize(model_name)
  end
end

class Car < Vehicle
  def initialize(model_name)
  end
end

那么,包含一个模块而不是一个超类呢?这样,你仍然可以 #kind_of? 工作,没有违约 new

module Vehicle
  def self.new(name)
    when 'mountain bike'
      Bike.new(name)
    when 'Ferrari'
      Car.new(name)
    ...
    end
  end
end

class Bike
  include Vehicle
end

class Car
  include Vehicle
end

class VehicleFactory
  def new() 
    if (wife_allows?)
       return Motorcycle.new
    else
       return Bicycle.new
    end
  end
end

class vehicleUser 
  def doSomething(factory)
    a_vehicle = factory.new()
  end
end

client.doSomething(Factory.new)
client.doSomething(Bicycle)    
client.doSomething(Motorcycle)

( Amazon link

你可以通过改变来清理一些东西 Vehicle#new 致:

class Vehicle
  def self.new(model_name = nil)
    klass = case model_name
      when 'mountain bike' then Bike
      # and so on
      else                      Car
    end
    klass == self ? super() : klass.new(model_name)
  end
end

class Bike < Vehicle
  def self.new(model_name)
    puts "New Bike: #{model_name}"
    super
  end
end

class Car < Vehicle
  def self.new(model_name)
    puts "New Car: #{model_name || 'unknown'}"
    super
  end
end

最后一行 Vehicle.new klass == self super 带括号。否则,我们最终会用争论来称呼它 没想到。

> Vehicle.new
New Car: unknown # from puts
# => #<Car:0x0000010106a480>

> Vehicle.new('mountain bike')
New Bike: mountain bike # from puts
# => #<Bike:0x00000101064300>

> Vehicle.new('ferrari')
New Car: ferrari # from puts
# => #<Car:0x00000101060688>