4 ms·

I don't see the difference to interfaces.

• deleted 12y ago
  [deleted]
• skj 12y ago
  The stuff you mix in has code. Interfaces do not.
  • jhasse 12y ago
    What code do you mean? He only wrote "pass". I guess I'm confused because he still used inheritance.
    • skj 12y ago
      There was a place to write code. In this example, obviously, none was written. But interfaces leave no opportunity.
• zo1 12y ago
  The difference is that those aren't interfaces. I'm confused by the question?
• Walkman 12y ago
  With interfaces, the above example would look like this: from abc import ABCMeta class PhysicsobjectMixin(ABCMeta): @abstractmethod def update_physics(self): pass @abstractmethod def apply_konckback(self, force): pass @abstractmethod def get_position(self): pass class FightMixin(ABCMeta): @abstractmethod def attack(self): pass @abstractmethod def defend(self): pass class TalkMixin(ABCMeta): @abstractmethod def say_something(self): pass class Character(PhysicsobjectMixin, FightMixin, TalkMixin): def update_physics(self): pass def apply_konckback(self, force): pass def get_position(self): pass def attack(self): pass def defend(self): pass def say_something(self): pass class Pickup(PhysicsobjectMixin): def update_physics(self): pass def apply_konckback(self, force): pass def get_position(self): pass class Projectile(PhysicsobjectMixin): def update_physics(self): pass def apply_konckback(self, force): pass def get_position(self): pass This is not DRY at all. I like mixins much better.
  • falcolas 12y ago
    It's not DRY, but then again, the chances of not overwriting, or more likely adding something to that method are pretty small when your project becomes more than an illustration of a principle. For example, what if you want to add custom animations any time your `Character` takes an action? Suddenly, all that boilerplate you "abstracted" away through mix-ins is back, with a vengeance. How about if your physics for a `Projectile` are different than for a `Pickup`? What if your character suddenly picks up a Sling of Thrown Voices, and needs to apply conversation snippets to its projectiles? In simple examples, mixins are great and reduce a lot of boilerplate, but in reality they are rarely so clean.
    • Walkman 12y ago
      > For example, what if you want to add custom animations any time your `Character` takes an action? What's wrong with this? class Character(PhysicsobjectMixin, FightMixin, TalkMixin): def attack(self): # custom attack animation here return super(Character, self).attack() def defend(self): # custom defend animation here return super(Character, self).defend() For me, it's still clear that 'attack' and 'defend' extends the funcionality of the 'FightMixin'. I can see even the first glance, those are inherited methods, because they use super() (call parent methods) > How about if your physics for a `Projectile` are different than for a `Pickup`? You need to implement two classes anyway. I see two possibilities: I. If you have to implement this kind of different physics behavior only for Projectile. (Maybe you don't even need a mixin.) class Projectile(object): def update_physics(self): pass def apply_konckback(self, force): pass def get_position(self): pass II. If you have more Projectile-like objects, but they are not all the same. class FastMovingPhysicsobjectMixin(object): def update_physics(self): pass def apply_konckback(self, force): pass def get_position(self): pass class Projectile(FastMovingPhysicsobjectMixin): pass class Arrow(FastMovingPhysicsobjectMixin): pass > What if your character suddenly picks up a Sling of Thrown Voices, and needs to apply conversation snippets to its projectiles? Is this a weapon which doesn't shoot projectiles, but make damage with voice or what? :D Then I think it's totally different, because if Character can have all kinds of different weapons and those behave different ways, mixins don't fit here. I would rather implement that like this: class Sword(object): def attack(self): # swing def defend(self): # defend class SlingOfThrownVoices(object): def attack(self): # shout loudly def defend(self): # pssszt, be quiet class Character(PhysicsobjectMixin, TalkMixin): def __init__(self, weapon): self.weapon = weapon def attack(self): # custom attack animation here self.weapon.attack() def defend(self): # custom defend animation here self.weapon.defend() then weapon can be instance of either Sword or SlingOfThrownVoices. Note that Mixins are still in use and no complicated inheritance problem occured even if you have hundreds of weapons.