确保typename类型是基数的派生 [英] Make sure that typename type is a Derived of Base

问题描述

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>  {

}

如何检查（编译时） T 是 cl2 类型或从cl2 和 C 是 cl1 类型或 。我需要确定cl2类型或 getTbyName 将是一个混乱。

How could I check (at compile time) that T is cl2 type or derived from cl2 and C is cl1 type or derived from cl1. I need to be sure about cl2 type or the getTbyName will be a mess.

谢谢您的时间< br>
Quentin

Thank you for your time
Quentin

推荐答案

您可以使用 static_assert 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>;
               ^

在线演示

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