Singleton

  • private constructor

      class Foo {
  private:
      Foo();
  }

  • a get_xxx() method looks like:

      static Foo *g_foo = NULL;
  Foo *get_foo() {
      if (!g_foo)
          g_foo = create_foo();
      return g_foo;
  }

Factory Method

  • also known as ‘Virtual Constructor’

  • delegate class instantiation to subclass

      +----------------+            +-----------------+
  |    Product     |            |    Creator      |
  +----------------+            +-----------------+
          A                     |                 |
          |                     +-----------------+
          |                     |+factoryMethod() |
          |                     +-----------------+
          |                              A
          |                              |
          |                              |
  +-----------------+           +-----------------+
  | ConcreteProduct |<-------<x>| ConcreteCreator |
  +-----------------+           +-----------------+
                                |                 |
                                +-----------------+
                                |+factoryMethod() |
                                +-----------------+

Observer

  • also known as ‘Publish Subcribe’
  • ‘MVC’ is a variant of Observer pattern?
  • when ‘publisher’ changes state, all registered ‘observer’s are notified and updated automatically

Decorator

  • also known as ‘Wrapper’
  • an alternative to subclassing for extending functionality

  • an example of Python decorator:

      def bar_decorator():
      def wrapper(func):
          print 'bar'
          func();
          print 'bar'
      return wrapper
    
  @bar_decorator
  def foo():
      print 'foo'

References

[1] “Design Patterns: Elements of Reusable Object-Oriented Software”