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abstract class CarPart { | |
CarPartType get type; | |
} | |
enum CarPartType<T extends CarPart> { | |
engine<Engine>(), | |
transmission<Transmission>(), | |
} | |
class Engine implements CarPart { | |
const Engine({ | |
required this.cylinders, | |
required this.horsepower, | |
}); | |
final int cylinders; | |
final int horsepower; | |
@override | |
CarPartType get type => CarPartType.engine; | |
} | |
class Transmission implements CarPart { | |
const Transmission({ | |
required this.gears, | |
required this.isManual, | |
}); | |
final int gears; | |
final bool isManual; | |
@override | |
CarPartType get type => CarPartType.transmission; | |
} | |
class Car { | |
const Car( | |
this.model, { | |
required this.parts, | |
}); | |
final String model; | |
final List<CarPart> parts; | |
String get description => [ | |
'These are the parts in a $model:', | |
for (final part in parts) '- ${_getDescriptionForCarPart(part)}', | |
'- And a whole bunch of other parts which I was too lazy to mention.', | |
].join('\n'); | |
} | |
String? _getDescriptionForCarPart(CarPart part) { | |
switch (part.type) { | |
case CarPartType.engine: | |
part as Engine; | |
return 'A ${part.cylinders} cylinder engine ' | |
'which makes ${part.horsepower}hp.'; | |
default: | |
part as Transmission; | |
return 'A ${part.gears} speed ' | |
'${part.isManual ? 'manual' : 'automatic'} transmission.'; | |
} | |
} | |
void main(List<String> args) => print( | |
const Car( | |
'Nissan Skyline GT-R', | |
parts: [ | |
Engine(cylinders: 6, horsepower: 300), | |
Transmission(gears: 7, isManual: true), | |
], | |
).description, | |
); |
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