确保typename类型是Derived of Base

Question

我有这种代码

template <typename D, typename T>
class tl1 {
    std::list<T> mTs ;
public:
    T & getTbyName() const ;
}

template <typename T, typename C>
class tl2 {
public:
    std::string getName() { return mName ; }
private:
    C & mC ;
    std::string mName
}

class c2 ;

class cl1 : tl1<cl1, cl2>  {

}
class cl2 : tl2<cl2, cl1>  {

}

我怎么能检查(在compile time)这T是cl2类型还是derived from cl2和C为cl1类型或derived from cl1.我需要确定cl2类型或getTbyName将是一个烂摊子.

谢谢你的时间
昆汀

Answer 1

你可以使用static_assert和std::is_base_of.

#include <type_traits>

struct B {};

template <typename T>
class C {
    static_assert(std::is_base_of<B, T>::value, "T should inherit from B");
};

struct D : public B {};
struct KO {};


template class C<B>;
template class C<D>;
template class C<KO>;

int main()
{
}

main.cpp: In instantiation of 'class C<KO>':
main.cpp:16:16:   required from here
main.cpp:7:5: error: static assertion failed: T should inherit from B
     static_assert(std::is_base_of<B, T>::value, "T should inherit from B");
     ^
======= clang =======
main.cpp:7:5: error: static_assert failed "T should inherit from B"
    static_assert(std::is_base_of<B, T>::value, "T should inherit from B");
    ^             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main.cpp:16:16: note: in instantiation of template class 'C<KO>' requested here
template class C<KO>;
               ^

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