A function that takes a discriminated union and writes it into a flexbuffer builder.

flexbuffer-building.cpp

flexbuffers::Builder& build(flexbuffers::Builder& builder, const data& x) {
  static auto to_uint = [](auto i) {
    return static_cast<std::underlying_type_t<detail::DataType>>(i);
  };
  struct converter {
    converter(flexbuffers::Builder& builder) : builder_{builder} {
    }
    void operator()(none) {
      builder_.UInt(to_uint(detail::DataType::NoneType));
    }
    void operator()(boolean x) {
      builder_.UInt(to_uint(detail::DataType::BooleanType));
      builder_.UInt(x ? 1 : 0);
    }
    void operator()(integer x) {
      builder_.UInt(to_uint(detail::DataType::IntegerType));
      builder_.Int(x);
    }
    void operator()(count x) {
      builder_.UInt(to_uint(detail::DataType::CountType));
      builder_.UInt(x);
    }
    void operator()(real x) {
      builder_.UInt(to_uint(detail::DataType::CountType));
      builder_.Double(x);
    }
    void operator()(timestamp x) {
      builder_.UInt(to_uint(detail::DataType::TimestampType));
      builder_.UInt(x.time_since_epoch().count());
    }
    void operator()(timespan x) {
      builder_.UInt(to_uint(detail::DataType::TimespanType));
      builder_.UInt(x.count());
    }
    void operator()(const enumeration& x) {
      builder_.UInt(to_uint(detail::DataType::EnumerationType));
      builder_.UInt(x);
    }
    void operator()(const std::string& x) {
      builder_.UInt(to_uint(detail::DataType::StringType));
      builder_.String(x);
    }
    void operator()(const pattern& x) {
      builder_.UInt(to_uint(detail::DataType::StringType));
      builder_.String(x.string());
    }
    void operator()(const address& x) {
      builder_.UInt(to_uint(detail::DataType::AddressType));
      if (x.is_v4()) {
        auto ptr = x.data().data() + 12;
        builder_.UInt(*reinterpret_cast<const uint32_t*>(ptr));
      } else {
        builder_.Blob(x.data().data(), x.data().size());
      }
    }
    void operator()(const subnet& x) {
      builder_.UInt(to_uint(detail::DataType::SubnetType));
      if (x.network().is_v4()) {
        auto ptr = x.network().data().data() + 12;
        builder_.UInt(*reinterpret_cast<const uint32_t*>(ptr));
      } else {
        builder_.Blob(x.network().data().data(), x.network().data().size());
      }
    }
    void operator()(const port& x) {
      builder_.UInt(to_uint(detail::DataType::PortType));
      builder_.UInt(x.number());
      builder_.UInt(static_cast<uint8_t>(x.type()));
    }
    void operator()(const vector& xs) {
      builder_.Vector([&] {
        for (auto& x : xs)
          visit(*this, x);
      });
    }
    void operator()(const set& xs) {
      builder_.UInt(to_uint(detail::DataType::SetType));
      builder_.Vector([&] {
        for (auto& x : xs)
          visit(*this, x);
      });
    }
    void operator()(const table& xs) {
    }
    flexbuffers::Builder& builder_;
  };
  builder.Vector([&]{
    visit(converter{builder}, x);
  });
  return builder;
}