Method hasValue

develop/matchit/patterns.h:805–814

                constexpr auto &variant() { return mVariant; }
                constexpr auto hasValue() const
                {
                    return std::visit(overload([](Type const &)
                                               { return true; },
                                               [](Type const *)
                                               { return true; },
                                               [](std::monostate const &)
                                               { return false; }),
                                      mVariant);
                }
                constexpr decltype(auto) value() const
                {
                    return std::visit(