Designing it twice does not need to take a lot of extra time. For a smaller module such as a class, you may not need more than an hour or two to consider alternatives. This is a small amount of time compared to the days or weeks you will spend implementing the class. The initial design experiments will probably result in a significantly better design, which will more than pay for the time spent designing it twice.
This is absolutely and completely true; glad to hear someone concur this; not that it's neccesary, i know it to be true.
