std :: is_same <A,B> :: value ==第1行为true，第2行为false

Question

I have a code that returns true in one line, false in the other.

For example,

struct Z{
    static const int value = 10;
};

struct A : Z{
};
struct B : Z{
};

int main(){
    if(std::is_same<A,B>::value){
        static_assert(std::is_same<A,B>::value , "why am i here?");
    }
    return 0;
}

Can someone please explain why it throws a static assert error?

Answer 1

This is because static_assert is a static (that is: compile time) assert. It does not care about the if statement (evaluated at run-time) above.