请问图中CPP代码编译器的处理过程是怎样的？

Question

请问下面代码编译器的处理过程是怎样的，详见代码

template<typename B, typename D>
class is_base_and_derived {
private:
  template<typename T>
  static int judge(D const *, T);
  static char judge(B const *, int);
  struct host {
    operator D const * () ;
    operator B const * () const ;
  };
public:
  enum { value = (is_same<B, D>::value || sizeof(int) == sizeof(judge(host(), 0))) };
};