“精心设计的类型”指的是在试图与typedef做朋友时出现的错误。

Let's say I have the following piece of code (a simple CRTP class hierarchy). I want to typedef the base class type to save myself typing (in my actual code, I use the base class type more than once and the base class takes several template parameters), and I need to befriend the base class since I want to keep the implementation private.Let's say I have the following piece of code (a