How to calculate the circumference of a circle based on the following Circle class?

Question

I have the following sealed Cirlce class
public sealed class Circle
private double radius;
public double Calculate(Func<double, double> op)
return op(radius);
I need to calculate the circumference of a (an arbitrary) circle based on this class without modifying the class.  Here is what I tried that is not working:
Circle cir = new Circle();
double circ = 2 * Math.PI * cir.Calculate(5, 5);
How can I calculate a circumference of a circle based on this scenario?
Rich P

Answer 1

Ok, let's clarify:
Facts:
1. The radius-field is private, and you can't set it via a public member like a method/property.
2. You don't want to change the class, but the radius
That means in other words you want to change a private field from outside of the class, which is not nice, but possible:
Circle cir = new Circle();
var field = cir.GetType().GetField("radius",BindingFlags.Instance|BindingFlags.NonPublic);
field.SetValue(cir, 5);
double circ = cir.Calculate((radius) => 2 * Math.PI * radius);
Ha, and now, did I manage to pass the skills test question? ;-)
Thomas Claudius Huber
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