Variadic xor template function --takes any types convertible to bool

variadic_xor.cpp

#include <cstddef>

namespace {
    /*
     * Helper function, variadic xor
     * It works by counting the number of true values and returning true only
     * if this number is 1.
     */

    template <typename T>
    constexpr std::size_t only_one_helper(T t) {
        return (bool)t;
    }

    template <typename T, typename... Args>
    constexpr std::size_t only_one_helper(T t, Args... args) { // recursive variadic function
        return only_one_helper(t) + only_one_helper(args...);
    }

    template <typename T, typename... Args>
    constexpr bool only_one(T t, Args... args) { // recursive variadic function
        return only_one_helper(t, args...) == 1;
    }
}

int main() {
    return only_one(false, true, true) or only_one(true, false, true, false);
}