Some objects can be doubled, for example a bank account. The result would be a bank account with twice the balance. Some objects can't be doubled. For example, there is no double of a dime coin—no twenty cent coin exists.
The Doubler interface (given below) describes a callback that can compute the doubling of a given object.
Your job is to provide a class RectangleDoubler that computes the doubling of a Rectangle. The doubling should have double the width and height, but the same x and y positions of the top left corner.