Oops! - "[Design Pattern] Summary"

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"