如何使用模板函数对数组项进行计数C++同时允许空数组

我使用以下模板函数来计算数组项：

#include <stdio.h>
template<typename T, size_t N> constexpr
size_t countof(T(&)[N])
{
return N;
}
int main(void)
{
struct {} arrayN[] = {{}, {}, {}};
printf("%zun", countof(arrayN));
return 0;
}

它有效，但不适用于空数组：

struct {} array0[] = {};
printf("%zun", countof(array0));

GCC 5.4 输出：

error: no matching function for call to ‘countof(main()::<anonymous struct> [0])’
note: candidate: template<class T, long unsigned int N> constexpr size_t countof(T (&)[N])
note:   template argument deduction/substitution failed:

如果我尝试添加专业化：

template<typename T> constexpr
size_t countof(T(&)[0])
{
return 0;
}

它甚至变得更奇怪：

error: no matching function for call to ‘countof(main()::<anonymous struct> [0])’
note: candidate: template<class T, long unsigned int N> constexpr size_t countof(T (&)[N])
note:   template argument deduction/substitution failed:
note: candidate: template<class T> constexpr size_t countof(T (&)[0])
note:   template argument deduction/substitution failed:
note:   template argument ‘-1’ does not match ‘#‘integer_cst’ not supported by dump_decl#<declaration error>’

我做错了什么？