Interfaces and restraints

Question

Considering the following setup, how can I restrain IConnection to only contain IPort of the same ConnectionType in Ports? Maybe I am overlooking something obvious here:

Enum ConnectionType
{
    Undefined,
    Type1,
    Type2
}


IConnection
{
    ConnectionType ConnectionType {get;set}
    IEnumerable<IPort> Ports {get;set;}
}

IPort
{
    ConnectionType ConnectionType {get;set;}
}

Answer 1

You cannot enforce such constraints at compile time.

You will have to do some checking at runtime.

Answer 2

In order to control the type of IPorts, you will need to change the class to not expose the list in a writeable manner.

Make the property read-only, returning a new ReadOnlyCollection to prevent adding any type of IPort to the internal collection. Add an AddPort method that will only allow adding an IPort of the right type.

Answer 3

Instead of having the connection type in the IPort interface, have a property of IConnection, e.g.

IConnection
{
  ConnectionType ConnectionType { get; }
  IEnumerable<IPort> Ports { get; }
}

IPort
{
  IConnection Connection { get; }
}

Management of these properties should be left to the implementation.

Answer 4

How about wrapping up the enum and using generics?

    public interface IConnectionType
{
    ConnectionTypeEnum Connection{ get; set;}
}

public enum ConnectionTypeEnum
{
   Undefined,
   Type1,
   Type2
}

public interface IPort<T> where T : IConnectionType
{
}

public interface IConnection<T> where T : IConnectionType
{
    IEnumerable<IPort<T>> Ports {get;set;}
}

I'm not sure if there's any point in having the enum anymore though