I'm trying to set up a rather complicated static_assertion to give people a clean error when they call my function. While I seem to be able to make it work, I don't understand why. I managed to boil it down to a relatively simple case that I don't understand (std::is_same is just used because it's simple). The following compiles happily:
template<typename T> constexpr bool IsInt(const T& t){
return std::is_same<decltype(t), const int&>::value;
}
template<typename T> bool CheckIsInt(const T& t){
auto s = t;
static_assert(IsInt(s), "T should be int");
return true;
}
On the other hand, if I get rid of the auto s = t, and just use IsInt(t), it fails:
template<typename T> bool CheckIsInt(const T& t){
static_assert(IsInt(t), "T should be int");
return true;
}
with the message (clang++-7):
static_assert expression is not an integral constant expression
What is going on? What's the difference?
