为什么这不是一个独立的名字？

问：

在类中，需要将变量编写为 ，以便使其成为将在基类中查找的依赖名称。D0mthis->m

但是在类中，编译器知道在基类中查找而不被写成 .D1mmthis->m

这怎么可能？为什么课堂上不需要写成？mD1this->m

#include <iostream>
#include <string>

template<class T>
class B
{
public:
    B(int i) : m(i) {}
    T* fb() {std::cout << "B::fb(): m = " << m << "\n"; return static_cast<T*>(this); }
protected:
    int m;
};

template<class T>
class D0 : public B<T>
{
public:
    D0(int i) : B<T>(i) {}
   /*
    * this-> makes this->m a dependent name so the lookup looks in the base class.  Without this->,
    * m would be an independent name and lookup would not check the base class.
    */
    T* fd0() {std::cout << "D0::fd0(): m = " << this->m << "\n"; return static_cast<T*>(this); }
};

class D1 : public D0<D1>
{
public:
    D1(int i) : D0<D1>(i) {}
   /*
    * D1 doesn't need m qualified by this-> because deriving from D0<D1> somehow
    * makes it unnecessary.
    */
    D1* fd1() {std::cout << "D1::fd1(): m = " << m << "\n"; return this; }
};

int main()
{
    std::string s;
    
    D1 d1(2);
    d1.fd1()->fd0()->fb()->fd0()->fd1();
    
    std::cout << "Press ENTER to exit\n";
    std::getline(std::cin, s);
}