Controlling inheritance with abstract

Now that we’ve covered some refactoring patterns around inheritance, let’s look at using abstract classes and other C# features to restrict our classes and ensure they’re used appropriately.

Communicating intent with abstract

One quirk about our current design is that it is possible to instantiate a new instance of FlightInfoBase simply by writing the following code:

FlightInfoBase flight = new FlightInfoBase();

While it might not make sense to you – for a new flight to exist that isn’t explicitly a passenger or freight flight, because the FlightInfoBase class is not marked as abstract – there’s nothing preventing anyone from instantiating it.

To mark a class as abstract, add the abstract keyword to its signature:

FlightInfoBase.cs

public abstract class FlightInfoBase : IFlightInfo {
  public Airport ArrivalLocation { get; set; }
  public DateTime ArrivalTime...