Ruby 工厂方法模式讲解和代码示例

工厂方法是一种创建型设计模式，解决了在不指定具体类的情况下创建产品对象的问题。

工厂方法定义了一个方法，且必须使用该方法代替通过直接调用构造函数来创建对象（ new操作符）的方式。子类可重写该方法来更改将被创建的对象所属类。

如果你不清楚工厂、 工厂方法和抽象工厂模式之间的区别，请参阅工厂模式比较。

进一步了解工厂方法模式

复杂度：

流行度：

使用示例： 工厂方法模式在 Ruby 代码中得到了广泛使用。当你需要在代码中提供高层次的灵活性时，该模式会非常实用。

识别方法： 工厂方法可通过构建方法来识别，它会创建具体类的对象，但以抽象类型或接口的形式返回这些对象。

概念示例

本例说明了工厂方法设计模式的结构并重点回答了下面的问题：

它由哪些类组成？
这些类扮演了哪些角色？
模式中的各个元素会以何种方式相互关联？

main.rb: 概念示例

# The Creator class declares the factory method that is supposed to return an
# object of a Product class. The Creator's subclasses usually provide the
# implementation of this method.
class Creator
  # Note that the Creator may also provide some default implementation of the
  # factory method.
  def factory_method
    raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
  end

  # Also note that, despite its name, the Creator's primary responsibility is
  # not creating products. Usually, it contains some core business logic that
  # relies on Product objects, returned by the factory method. Subclasses can
  # indirectly change that business logic by overriding the factory method and
  # returning a different type of product from it.
  def some_operation
    # Call the factory method to create a Product object.
    product = factory_method

    # Now, use the product.
    "Creator: The same creator's code has just worked with #{product.operation}"
  end
end

# Concrete Creators override the factory method in order to change the resulting
# product's type.
class ConcreteCreator1 < Creator
  # Note that the signature of the method still uses the abstract product type,
  # even though the concrete product is actually returned from the method. This
  # way the Creator can stay independent of concrete product classes.
  def factory_method
    ConcreteProduct1.new
  end
end

class ConcreteCreator2 < Creator
  # @return [ConcreteProduct2]
  def factory_method
    ConcreteProduct2.new
  end
end

# The Product interface declares the operations that all concrete products must
# implement.
class Product
  # return [String]
  def operation
    raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
  end
end

# Concrete Products provide various implementations of the Product interface.
class ConcreteProduct1 < Product
  # @return [String]
  def operation
    '{Result of the ConcreteProduct1}'
  end
end

class ConcreteProduct2 < Product
  # @return [String]
  def operation
    '{Result of the ConcreteProduct2}'
  end
end

# The client code works with an instance of a concrete creator, albeit through
# its base interface. As long as the client keeps working with the creator via
# the base interface, you can pass it any creator's subclass.
def client_code(creator)
  print "Client: I'm not aware of the creator's class, but it still works.\n"\
        "#{creator.some_operation}"
end

puts 'App: Launched with the ConcreteCreator1.'
client_code(ConcreteCreator1.new)
puts "\n\n"

puts 'App: Launched with the ConcreteCreator2.'
client_code(ConcreteCreator2.new)

output.txt: 执行结果

App: Launched with the ConcreteCreator1.
Client: I'm not aware of the creator's class, but it still works.
Creator: The same creator's code has just worked with {Result of the ConcreteProduct1}

App: Launched with the ConcreteCreator2.
Client: I'm not aware of the creator's class, but it still works.
Creator: The same creator's code has just worked with {Result of the ConcreteProduct2}

Ruby 工厂方法模式讲解和代码示例

概念示例

main.rb: 概念示例

output.txt: 执行结果

工厂方法在其他编程语言中的实现