Overload macro as variable and function

First, there are a lot of posts on overloading macros:

• Can macros be overloaded by number of arguments?
• C++ Overloading Macros
• Macro overloading
• Overloading Macro on Number of Arguments
• etc. ...

However, all of them ask the question about variadic macros.

What I'd like to ask is if the following is possible:

#define FOO 3
#define FOO(a,b) a+b

int main() {
  int a = FOO(0,1);
  int b = FOO;
  std::cout << a + b;
  return 0;
}

I'd like for it to work on clang as well.

It's not a macro, but looks like it

struct SmartMacro {
    constexpr operator int() const noexcept { return 3; }
    constexpr int operator()(int a, int b) const noexcept { return a + b; }
};
constexpr SmartMacro FOO;

int main() {
    int a = FOO(0,1);
    int b = FOO;
    std::cout << a + b;
    return 0;
}