Question

MasterClass is the base class, Attachvariable inherits from this. Table stores MasterClass objects.

public class Table
{
    private Dictionary<int, MasterClass> map = new Dictionary<int, MasterClass>();

    public bool isInMemory(int id)
    {
        if (map.ContainsKey(id))
            return true;
        return false;
    }

    public void doStuffAndAdd(MasterClass theclass)
    {
        theclass.setSomething("lalala");
        theclass.doSomething();
        map[theclass.id] = theclass;
    }

    public MasterClass getIt(int id)
    {
        return map[id];
    }
}

So now this happens:

Table table = new Table();
if (!table.isInMemory(22))
{
    Attachvariable attachtest = new Attachvariable(22);
    table.doStuffAndAdd(attachtest);
    Console.WriteLine(attachtest.get_position()); //Get_position is a function in Attachvariable 
}
else
{
    Attachvariable attachtest = table.getIt(22); //Error: Can't convert MasterClass to Attachvariable
    Console.WriteLine(attachtest.get_position());
}

Is there any way to make Table work with any class that inherits from MasterClass, without knowing about that class’ existance up front, so that I can still use doStuffAndAdd(MasterClass theclass) and also use Attachvariable as a return type for getIt().

I can’t use Table<T> because then doStuffAndAdd can’t add a MasterClass object to the Dictionary. There’s no way to check if T inherits from MasterClass so that’s not suprising… how do I make this work?

public class Table<T>
{
    private Dictionary<int, T> map = new Dictionary<int, T>();

    public bool isInMemory(int id)
    {
        if (map.ContainsKey(id))
            return true;
        return false;
    }

    public void doStuffAndAdd(MasterClass theclass)
    {
        theclass.setSomething("lalala");
        theclass.doSomething();
        map[theclass.id] = theclass; //Error: can't convert MasterClass to T
    }

    public T getIt(int id)
    {
        return map[id];
    }
}

Answer 1

I believe this:

public void doStuffAndAdd(MasterClass theclass)
    {
        theclass.setSomething("lalala");
        theclass.doSomething();
        map[theclass.id] = theclass; //Error: can't convert MasterClass to T
    }

has to be

public void doStuffAndAdd(T theclass)
    {
        theclass.setSomething("lalala");
        theclass.doSomething();
        map[theclass.id] = theclass; //should work 
    }

You can check if a class inherits another by doing:

if(theclass is MasterClass)
{}