(cppcon)Declarative Control Flow

class UncaughtExceptionCounter {
	int getUncaughtExceptionCount() noexcept;
	int exceptionCount_ ;
public:
	UncaughtExceptionCounter()
	: exceptionCount_ (std::uncaught_exceptions()) {
	}
	bool newUncaughtException() noexcept {
		return std::uncaught_exceptions() > exceptionCount _ ;
	}
};

template <typename FunctionType, bool executeOnException>
class ScopeGuardForNewException {
	FunctionType function_ ;
	UncaughtExceptionCounter ec_ ;
public:
	explicit ScopeGuardForNewException(const FunctionType& fn)
	: function_ (fn) {}
	explicit ScopeGuardForNewException(FunctionType&& fn)
	: function_ (std::move(fn)) {}
	~ScopeGuardForNewException() noexcept(executeOnException) {
		if (executeOnException == ec_.isNewUncaughtException()) {
			function_ ();
		}
	}
};

enum class ScopeGuardOnFail {};

template <typename FunctionType>
ScopeGuardForNewException<typename std::decay<FunctionType>::type, true>
operator+(detail::ScopeGuardOnFail, FunctionType&& fn) {
	return ScopeGuardForNewException<
		typename std::decay<FunctionType>::type, true>(
			std::forward<FunctionType>(fn));
}

#define SCOPE_FAIL \
	auto ANONYMOUS_VARIABLE(SCOPE_ FAIL_STATE) \
		= ::detail::ScopeGuardOnFail() + [&]() noexcept