calling derived methods on a baseclass collection

Question

I have one abstract class named A, and other classes (B, C, D, E, ...) that implements A. My derived classes are holding values of different types. I also have a list of A objects.

    abstract class A { }
    class B : class A
    {
      public int val {get;private set;}
    }
    class C : class A
    {
      public double val {get;private set;}
    }
    class D : class A
    {
      public string val {get;private set;}
    }

    class Program
    {
        static void Main(string[] args)
        {
          List list = new List { new B(), new C(), new D(), new E() };
          // ... 

          foreach (A item in list)
          {
            Console.WriteLine(String.Format("Value is: {0}", item.val);
          }
        }
    }

...where the .val is not known by the base-class ofc.

How can i get this dynamic behaviour? I don't want to use getType in a long switch/if-statements.

Answer 1

If you just want to get the string representation of val i recoment overriding ToString in each of the sub classes

public override string ToString()
{
    return val.ToString();
}

either way if you want the data in a sub class you need to represent it in the base class as some type they all have in common (like object). and you could do it like this

abstract class A 
{
    public abstract object GetValue();
}
class B : class A
{
    public int val {get;private set;}
    public override object GetValue()
    {
        return val;
    }
}