Question

这是我的基本测试代码：

#include <iostream>
#include <variant>

int main(int argc, char** argv) {
    std::variant<int> v{5};
    std::cout << std::get<0>(v) << std::endl;
}

当我使用Clang编译它时，如下所示：clang++ -std=c++1z -g Sources/main.cpp 我收到了这些错误：

In file included from Sources/main.cpp:2:
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/7.1.1/../../../../include/c++/7.1.1/variant:235:46: error: cannot cast 'std::variant<int>' to its private base class
      'std::__detail::__variant::_Variant_storage<true, int>'
      return __get(std::in_place_index<_Np>, std::forward<_Variant>(__v)._M_u);
                                             ^
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/7.1.1/../../../../include/c++/7.1.1/variant:1192:35: note: in instantiation of function template specialization
      'std::__detail::__variant::__get<0, std::variant<int> &>' requested here
      return __detail::__variant::__get<_Np>(__v);
                                  ^
Sources/main.cpp:6:20: note: in instantiation of function template specialization 'std::get<0, int>' requested here
        std::cout << std::get<0>(v) << std::endl;
                          ^
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/7.1.1/../../../../include/c++/7.1.1/variant:878:7: note: constrained by private inheritance here
    : private __detail::__variant::_Variant_base<_Types...>,
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/7.1.1/../../../../include/c++/7.1.1/variant:235:74: error: '_M_u' is a private member of
      'std::__detail::__variant::_Variant_storage<true, int>'
      return __get(std::in_place_index<_Np>, std::forward<_Variant>(__v)._M_u);
                                                                         ^
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/7.1.1/../../../../include/c++/7.1.1/variant:878:7: note: constrained by private inheritance here
    : private __detail::__variant::_Variant_base<_Types...>,
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/7.1.1/../../../../include/c++/7.1.1/variant:377:34: note: member is declared here
      _Variadic_union<_Types...> _M_u;

但是当我用GCC编译时，使用相同的选项，我没有任何错误，我得到了正确的输出（5）。

所以我想知道它是否真的是一个实现错误，或者它是否来自我。

std :: variant实现错误（Clang 4.0.1）

0 个答案: