The only meaning we can ascribe to a template parameter is to distinguish whether the parameter is a type parameter or a nontype parameter.
可以给模板形参赋予的唯一含义是区别形参是类型形参还是非类型形参。
英语百科
TypeParameter
（重定向自Type parameter）
In computer programming languages, TypeParameter is a frequently used generic label used in templates to reference an unknown data type, data structure, or class. Templates are most frequently used in Java and C++. TypeParameter is similar to a metasyntactic variable (e.g., foo and bar), but distinct. It is not the name of a generic variable, but the name of a generic type of variable.