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模板方法

模板方法在 Ruby 中的实现

Template Method is a behavioral design pattern that allows you to defines a skeleton of an algorithm in a base class and let subclasses override the steps without changing the overall algorithm's structure.

进一步了解模板方法模式

在 Ruby 中使用模式

复杂度:

流行度:

使用示例: The Template Method pattern is quite common in Ruby frameworks. Developers often use it to provide framework users with a simple means of extending standard functionality using inheritance.

识别方法: Template Method can be recognized by behavioral methods that already have a "default" behavior defined by the base class.

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

模板方法在其他编程语言中的实现

模板方法 在 Java 中的实现 模板方法 在 C# 中的实现 模板方法 在 PHP 中的实现 模板方法 在 Python 中的实现 模板方法 在 Swift 中的实现 模板方法 在 TypeScript 中的实现