83 lines
1.9 KiB
Python
83 lines
1.9 KiB
Python
from typing import TypeVar, Generic
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class Beverage:
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"""Any beverage"""
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class Juice(Beverage):
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"""Any fruit juice"""
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class OrangeJuice(Juice):
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"""Delicious juice from Brazilian oranges"""
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BeverageT = TypeVar('BeverageT', covariant=True)
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class BeverageDispenser(Generic[BeverageT]):
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def __init__(self, beverage: BeverageT) -> None:
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self.beverage = beverage
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def dispense(self) -> BeverageT:
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return self.beverage
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class Garbage:
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"""Any garbage."""
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class Biodegradable(Garbage):
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"""Biodegradable garbage."""
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class Compostable(Biodegradable):
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"""Compostable garbage."""
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GarbageT = TypeVar('GarbageT', contravariant=True)
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class TrashCan(Generic[GarbageT]):
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def put(self, trash) -> None:
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"""Store trash until dumped..."""
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class Cafeteria:
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def __init__(
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self,
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dispenser: BeverageDispenser[Juice],
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trash_can: TrashCan[Biodegradable]
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):
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"""Initialize..."""
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beverage_dispenser = BeverageDispenser(Beverage())
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juice_dispenser = BeverageDispenser(Juice())
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orange_juice_dispenser = BeverageDispenser(OrangeJuice())
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trash_can: TrashCan[Garbage] = TrashCan()
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bio_can: TrashCan[Biodegradable] = TrashCan()
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compost_can: TrashCan[Compostable] = TrashCan()
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arnold_hall = Cafeteria(juice_dispenser, bio_can)
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######################## covariance on 1st argument
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arnold_hall = Cafeteria(orange_juice_dispenser, trash_can)
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## Argument 1 to "Cafeteria" has
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## incompatible type "BeverageDispenser[Beverage]"
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## expected "BeverageDispenser[Juice]"
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# arnold_hall = Cafeteria(beverage_dispenser, trash_can)
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######################## contravariance on 2nd argument
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## Argument 2 to "Cafeteria" has
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## incompatible type "TrashCan[Compostable]"
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## expected "TrashCan[Biodegradable]"
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# arnold_hall = Cafeteria(juice_dispenser, compost_can)
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arnold_hall = Cafeteria(juice_dispenser, trash_can)
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