On 2017-10-28 11:31 PM, Koos Zevenhoven wrote:
On Sat, Oct 28, 2017 at 11:24 PM, Soni L. <fakedme...@gmail.com
<mailto:fakedme...@gmail.com>>wrote:
On 2017-10-28 02:51 PM, Steven D'Aprano wrote:
You ignored my question: Is that the sort of thing you mean by
composition? If not, then what do you mean by it? This is not a
rhetorical question: I'm having difficulty understanding your
proposal.
It is too vague, and you are using terminology in ways I don't
understand.
Maybe that's my ignorance, or maybe you're using non-standard
terminology. Either way, if I'm having trouble, probably
others are too.
Help us understand your proposal.
I have to say I'm almost impressed by the constructiveness of the
discussion, even though I still don't understand the point of all the
square brackets in the proposal.
With composition, you can have car.key.turn() call
car.ignition.start(), without having to add car to key or ignition
to key. You just have to put both in a car and they can then see
eachother!
Here it's a bit confusing that the key is thought of as part of the
car. It's easy to imagine that an owner of two cars would want the
same key to work for both of them. Or that one car could have multiple
users with non-identical keys. I'm not sure if these things already
exist in real life, but if not, it's probably just a matter of time.
But let's ignore this confusion for a moment, and imagine that the
example makes perfect sense. Now, it sounds like you want something
like namespacing for methods and attributes within a complicated
class. Maybe you could implement it using nested classes and
decorators to make sure 'self' is passed to to the methods in the way
you want. The usage might look roughly like:
@namespacedclass
class Car:
@classnamespace
class ignition:
def start(self):
...
@classnamespace
class key:
def turn(self):
self.ignition.start()
Another concern regarding the example, however, is that this seems to
make it unclear what the public API of the car is. It looks like you
can just as easily drive the car without having the key: just call
car.ignition.start().
It's a crap example, yes.
But you should be able to do things like
car = object()
car[Engine] = SimpleEngine()
car.[Engine].kickstart() # calls kickstart method with an instance of
SimpleEngine as `self`/first argument and `car` as second argument.
# etc
Which your decorator-based approach quite obviously doesn't let you.
-- Koos
--
+ Koos Zevenhoven + http://twitter.com/k7hoven +
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