DRY 是一个最简单的法则，也是最容易被理解的。但它也可能是最难被应用的（因为要做到这样，我们需要在泛型设计上做相当的努力，这并不是一件容易的事）。-DRY is one of the most simple rules, also the most easily understood. But it may also be the most difficult to be applied (because to do so, we need to do in the generic desig