c++ - 继承返回 *this 的成员函数

Question

为什么 *this的 derived<T>类仍然是base<T>类型？

我以为 typename X会处理的。

如果这看起来很难看，什​​么是更好的方法？

失败的尝试:

template <typename T>
class Derived;

template <typename T, typename X>
class Base{
    public:
        T val;
        X f(void){
            return *this;
        }
};

template <typename T>
class Derived: public Base<T, Derived<T> >{
};


int main(void){
    Derived<int> B;
    Derived<int> C = B.f();
}

错误:

test4.cpp(9): error: no suitable user-defined conversion from "Base<int, Derived<int>>" to "Derived<int>" exists
              return *this;
                     ^
          detected during instantiation of "X Base<T, X>::f() [with T=int, X=Derived<int>]" at line 20

compilation aborted for test4.cpp (code 2)

Answer 1

你可以用以下方式来做沮丧:

X f(){ return static_cast<X&>(*this);}