c++ - 在类型实例化期间强制触发 static_assert

Question

如何在这个给定的类中强制使用 static_assert:

template < int I >
struct foo
{
    static_assert( I < 5 ,"I must be smaller than 5!" );
};

当我实例化模板时触发 no 当我实例化结果类型时:

int main()
{
    typedef foo< 5 > t; // compiles
    t tt; // will not compile 
}

Answer 1

一个建议

template <int I>
struct foo_guard {
  static_assert(I < 5, "I must be smaller than 5!");
  typedef void type;
};
template < int I, typename = typename foo_guard<I>::type>
struct foo
{
};