more readable macro to replace std::holds_alternative

isa_macro

/ IS_ / IS_NOT_ replacement of std::holds_alternative
// Inspiration: https://youtu.be/raB_289NxBk?t=1088
// Usage:
//
//     if (someVariantVar IS_(AlternativeType)) { ...
//     if (someVariantVar IS_NOT_(AlternativeType)) { ...
//
// Precedence: same as binary *
//
#define IS_(TYPE)     *::clai::IsInitiator<TYPE, false>()
#define IS_NOT_(TYPE) *::clai::IsInitiator<TYPE, true>()

template <typename T, bool Invert>
class IsInitiator {};

template <typename T, bool Invert, typename... Types>
constexpr bool operator*(const std::variant<Types...>& v,
                         const IsInitiator<T, Invert>&) noexcept {
  return std::holds_alternative<T>(v) ^ Invert;
}