Ruby 模板方法模式讲解和代码示例

模版方法是一种行为设计模式，它在基类中定义了一个算法的框架，允许子类在不修改结构的情况下重写算法的特定步骤。

进一步了解模板方法模式

复杂度：

流行度：

使用示例： 模版方法模式在 Ruby 框架中很常见。开发者通常使用它来向框架用户提供通过继承实现的、对标准功能进行扩展的简单方式。

识别方法： 模版方法可以通过行为方法来识别，该方法已有一个在基类中定义的 “默认” 行为。

概念示例

本例说明了模板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 Abstract Class defines a template method that contains a skeleton of some
# algorithm, composed of calls to (usually) abstract primitive operations.
#
# Concrete subclasses should implement these operations, but leave the template
# method itself intact.
class AbstractClass
  # The template method defines the skeleton of an algorithm.
  def template_method
    base_operation1
    required_operations1
    base_operation2
    hook1
    required_operations2
    base_operation3
    hook2
  end

  # These operations already have implementations.

  def base_operation1
    puts 'AbstractClass says: I am doing the bulk of the work'
  end

  def base_operation2
    puts 'AbstractClass says: But I let subclasses override some operations'
  end

  def base_operation3
    puts 'AbstractClass says: But I am doing the bulk of the work anyway'
  end

  # These operations have to be implemented in subclasses.
  def required_operations1
    raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
  end

  # @abstract
  def required_operations2
    raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
  end

  # These are "hooks." Subclasses may override them, but it's not mandatory
  # since the hooks already have default (but empty) implementation. Hooks
  # provide additional extension points in some crucial places of the algorithm.

  def hook1; end

  def hook2; end
end

# Concrete classes have to implement all abstract operations of the base class.
# They can also override some operations with a default implementation.
class ConcreteClass1 < AbstractClass
  def required_operations1
    puts 'ConcreteClass1 says: Implemented Operation1'
  end

  def required_operations2
    puts 'ConcreteClass1 says: Implemented Operation2'
  end
end

# Usually, concrete classes override only a fraction of base class' operations.
class ConcreteClass2 < AbstractClass
  def required_operations1
    puts 'ConcreteClass2 says: Implemented Operation1'
  end

  def required_operations2
    puts 'ConcreteClass2 says: Implemented Operation2'
  end

  def hook1
    puts 'ConcreteClass2 says: Overridden Hook1'
  end
end

# The client code calls the template method to execute the algorithm. Client
# code does not have to know the concrete class of an object it works with, as
# long as it works with objects through the interface of their base class.
def client_code(abstract_class)
  # ...
  abstract_class.template_method
  # ...
end

puts 'Same client code can work with different subclasses:'
client_code(ConcreteClass1.new)
puts "\n"

puts 'Same client code can work with different subclasses:'
client_code(ConcreteClass2.new)

output.txt: 执行结果

Same client code can work with different subclasses:
AbstractClass says: I am doing the bulk of the work
ConcreteClass1 says: Implemented Operation1
AbstractClass says: But I let subclasses override some operations
ConcreteClass1 says: Implemented Operation2
AbstractClass says: But I am doing the bulk of the work anyway

Same client code can work with different subclasses:
AbstractClass says: I am doing the bulk of the work
ConcreteClass2 says: Implemented Operation1
AbstractClass says: But I let subclasses override some operations
ConcreteClass2 says: Overridden Hook1
ConcreteClass2 says: Implemented Operation2
AbstractClass says: But I am doing the bulk of the work anyway

Ruby 模板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

模板方法在其他编程语言中的实现