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#include <iostream>
using namespace std;
class VehicleBase
{
// original Vehicle members, not implementing the
// redefinable interface, but used as a implementable rather than
// instantiatable part of the corresponding class template.
// That's why it declares its corresponding class template a friend.
template <class Derived>
friend class Vehicle;
size_t d_massFactor = 1;
};
template <class Derived>
class Vehicle: public VehicleBase
{
public:
int mass() const
{
return d_massFactor *
static_cast<Derived const *>(this)->vmass();
}
};
class CarBase: public VehicleBase
{
// original Car members, not implementing the
// redefinable interface
int x = 1000;
friend class Car;
};
class Car: public CarBase, public Vehicle<Car>
{
friend class Vehicle<Car>;
int vmass() const
{
return x;
}
};
class TruckBase: public CarBase
{
// original Truck members, not implementing the
// redefinable interface
friend class Truck;
};
class Truck: public TruckBase, public Vehicle<Truck>
{
friend class Vehicle<Truck>;
private:
int vmass() const
{
return 15000;
}
};
template <class Vehicle>
void fun(Vehicle &vehicle)
{
cout << vehicle.mass() << '\n';
}
int main()
{
Car car;
fun(car);
Truck truck;
fun(truck);
}
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