4 ms·

> Decorator is Python’s implementation to visitor pattern... huh?

• didip 17y ago
  Visitor patterns add new functionality to existing object structure [http://en.wikipedia.org/wiki/Visitor_pattern http://en.wikipedia.org/wiki/Visitor_pattern]. Python decorator does not do that?
  • tetha 17y ago
    The decorator syntax @decorator2 @decorator1 def foo(*args): pass is just a shorthand for def foo(*args): pass foo = decorator2(decorator1(foo)) I completely fail to see the visitor pattern here, even with stretching until breaking.
    • didip 17y ago
      Python decorator can do more than just that. @decorator1 can be a completely different class which manipulate foo.__class__
      • tetha 17y ago
        Certainly, it is an arbitrary python function, so the resulting foo might be a dictionary or whatever. But this doesn't push it closer to the visitor pattern. Certainly, you can use decorators as a tool to implement the visitor pattern by implementing some hairy, magical reflecting class-decorator which adds a method visit to an object, which then calls visit_{CLASSNAME} on the parameter, but this is just a way of implementing this and not the visitor pattern in itself.