Thread: Solving type of class

This is kinda lengthy but I am curious if there is a neat solution to this

I have a class like so

Code:

public abstract class Entity
{
    public abstract void Draw(Graphics g);
    public static Vector Intersect(Line line1, Line line2)
    {
         //Do stuff
    }
    public static Vector Intersect(Arc arc1, Arc arc2)
    {
         //Do stuff
    }
}

Then I have two classes like this

Code:

public class Line : Entity
{
    override public void Draw(Graphics g)
    {
        //Draw stuff
    }
}

public class Arc : Entity
{
    override public void Draw(Graphics g)
    {
        //Draw stuff
    }
}

I now can do this

Code:

private void MainWin_Paint(e)
{
    foreach(Entity entity in m_alVisableEntities)
    {
        Graphics g = e.Graphics;
        entity.Draw(g);	
    }
}

What happens here is that at run time the program call the correct draw function , either Arc or Line.

But if I try to do this

Code:

vIntersection = Entity.Intersection(m_Entity1, m_Entity2);

where m_Entity1 and m_Entity2 are Entity containg Line instances. I get a compile time error saying something like "cannot convert argument from Entity to Line"

Why is it that in the first case the compiler can solve what type of entity I am calling but not in the second case. And is there a decent way to solve it without manually doing type checking?

Thanks

~Barjor