Can a C++ function be declared such that the return value cannot be ignored?

Question

I\'m trying to determine whether a C++ function can be declared in such a way that the return value cannot be ignored (ideally detected at compile time). I tried to declare

Answer 1

See __attribute__ ((warn_unused_result)).

int foo() __attribute__ ((warn_unused_result));
int foo(){return 123;}

int main()
{
    foo(); //compiler warning
    auto i = foo(); //valid
}

Then force the warning to be an error:

clang++ -std=c++1z -Werror="unused-result"