interface IFoo
{
  IVehicle vehicle;
}

interface IVehicle { }

interface ICar : IVehicle { }

class Car : ICar { }

class Foo : IFoo
{
  public IVehicle vehicle;

  public Foo(ICar car)
  {
    this.vehicle = car;
  }
}

interface IFactory
{
  IFoo Produce();
}

class Factory : IFactory
{
  public IFoo Produce()
  {
    return new Foo(new Car());
  }
}