With explicit conversion operators you can fix this: "if (-0.5 <= x <= 0.5) return 0;" for x that are not built-in types. You would need to create your own Bool

With explicit conversion operators you can fix this: "if (-0.5 <= x <= 0.5) return 0;" for x that are not built-in types. You would need to create your own Bool type, something like defined below, and overload <= operators for x type, returning Bool. This way you will get compile time error. class Bool { bool value; public: Bool(bool v) : value(v) {} explicit operator bool () { return value; } };