Dart: Base class
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To enforce inheritance of a class or mixin’s implementation, use the base modifier. A base class disallows implementation outside of its own library. This guarantees:
The base class constructor is called whenever an instance of a subtype of the class is created.
All implemented private members exist in subtypes.
A new implemented member in a
baseclass does not break subtypes, since all subtypes inherit the new member.- This is true unless the subtype already declares a member with the same name and an incompatible signature.
You must mark any class which implements or extends a base class as base, final or sealed. This prevents outside libraries from breaking the base class guarantees.
// Library a.dart
base class Vehicle {
void moveForward(int meters) {
// ...
}
}
// Library b.dart
import 'a.dart';
// Can be constructed
Vehicle myVehicle = Vehicle();
// Can be extended
base class Car extends Vehicle {
int passengers = 4;
// ...
}
// ERROR: Cannot be implemented
base class MockVehicle implements Vehicle {
@override
void moveForward() {
// ...
}
}
