如何在Swift中使用泛型实现“C ++ - ish模板专业化”？

I realize generics and templates are different, but I thought I'd throw out the C++-ish remark since someone familiar with templates would know what I am trying to accomplish. In the code below, I am trying to write one generic member method that handles strings in one overload variant. In the other variant, the method is supposed to handle numerical types that can be initialized from a string. I realize generics and templates are different,