Question

I have next code that represents graph edges and nodes (simplified for question):

public class Node
{
}

public class Edge
{
    public Node Source { get; set; }
    public Node Target { get; set; }
}

Now I want to extend this classes for describing mine topology:

public class MineNode : Node
{
    public double FanPressure { get; set; }
}

public class MineTunnel : Edge
{
    public double Length { get; set; }
    public double CrossSectionArea { get; set; }

    public MineTunnel()
    {
        Source = new MineNode();
        Target = new MineNode();
    }
}

The problem is that I want to access additional data provided by MineNode when using Source and Target properties, but I can access only Node fields because they are declared in base class:

MineTunnel t = new MineTunnel();
Console.WriteLine(t.Source.FanPressure); //Error

The only way to access FanPressure is to cast Source to MineNode but code become ugly this way.

Console.WriteLine(((MineNode)t.Source).FanPressure); //OK

The another way is maybe to use somehow generics in base class declaration. But I’m not sure is that a good practice in my situation.

So, how can I solve such problem – extend functionality of base class fields?

Thanks.

Answer 1

I think generics is the way to go here…

Try this:

public class Node
{

}

public class Edge<S, T>
    where S : Node
    where T : Node
{
    public S Source { get; set; }
    public T Target { get; set; }
}

Then you can extend the Node and Edge classes with:

public class MineNode : Node
{
    public double FanPressure { get; set; }
}

public class MineTunnel : Edge<MineNode, MineNode>
{
    public double Length { get; set; }
    public double CrossSectionArea { get; set; }

    public MineTunnel()
    {
        Source = new MineNode();
        Target = new MineNode();
    }
}

Please correct me if this is wrong or doesn’t work… 🙂

MineTunnel t = new MineTunnel();
Console.WriteLine(t.Source.FanPressure); // Now this works without errors ;)