gcc 中的默认构造内联静态随机数引擎

Question

例如，

#include <random>

struct stru {
  //inline static std::mt19937 rnd; Oops!
  inline static std::mt19937 rnd{};  
};

int main() {

}

我看不出两者在语义上的区别，clang 编译两者都没有问题。然而gcc 8.1 第一个产生以下错误：

prog.cc:4:30: error: no matching function for call to 'std::mersenne_twister_engine<long unsigned int, 32, 624, 397, 31, 2567483615, 11, 4294967295, 7, 2636928640, 15, 4022730752, 18, 1812433253>::mersenne_twister_engine()'
   inline static std::mt19937 rnd;
                              ^~~
In file included from /opt/wandbox/gcc-8.1.0/include/c++/8.1.0/random:49,
                 from prog.cc:1:
/opt/wandbox/gcc-8.1.0/include/c++/8.1.0/bits/random.h:437:11: note: candidate: 'constexpr std::mersenne_twister_engine<long unsigned int, 32, 624, 397, 31, 2567483615, 11, 4294967295, 7, 2636928640, 15, 4022730752, 18, 1812433253>::mersenne_twister_engine(const std::mersenne_twister_engine<long unsigned int, 32, 624, 397, 31, 2567483615, 11, 4294967295, 7, 2636928640, 15, 4022730752, 18, 1812433253>&)'
     class mersenne_twister_engine
           ^~~~~~~~~~~~~~~~~~~~~~~
/opt/wandbox/gcc-8.1.0/include/c++/8.1.0/bits/random.h:437:11: note:   candidate expects 1 argument, 0 provided
/opt/wandbox/gcc-8.1.0/include/c++/8.1.0/bits/random.h:437:11: note: candidate: 'constexpr std::mersenne_twister_engine<long unsigned int, 32, 624, 397, 31, 2567483615, 11, 4294967295, 7, 2636928640, 15, 4022730752, 18, 1812433253>::mersenne_twister_engine(std::mersenne_twister_engine<long unsigned int, 32, 624, 397, 31, 2567483615, 11, 4294967295, 7, 2636928640, 15, 4022730752, 18, 1812433253>&&)'
/opt/wandbox/gcc-8.1.0/include/c++/8.1.0/bits/random.h:437:11: note:   candidate expects 1 argument, 0 provided

这是一个 gcc 错误（不是我的代码也不是 libstdc++），对吧？

Answer 1

这是一个 gcc 错误（不是我的代码也不是 libstdc++），对吧？

没错。使用这个简短的 sn-p 可以更轻松地复制它：

struct test {
    explicit test() {};
};

struct stru {
    inline static test t; 
};

int main() {
    test t;
}

explicit 说明符正在抛弃 GCC。必须调用相同的 c'tor 来初始化静态内联成员和局部变量。然而 GCC 很好地初始化了局部变量，但抱怨内联静态成员。