static void add_number(rapidjson::Value &target, const char* name, float_2 src, Document::AllocatorType& alloc)
{
    std::ostringstream ss;
    ss << src.x << " " << src.y;
    std::string s(ss.str());
    target.AddMember(StringRef(name), s, alloc);
}

static void add_number(rapidjson::Value &target, const char* name, float_3 src, Document::AllocatorType& alloc)
{
    std::ostringstream ss;
    ss << src.x << " " << src.y << " " << src.z;
    std::string s(ss.str());
    target.AddMember(StringRef(name), s, alloc);
}

template <typename T>
static void add_number(rapidjson::Value &target, const char* name, T src, Document::AllocatorType& alloc)
{
    std::ostringstream ss;
    switch(src.size){
      case 2: ss << src.x << " " << src.y;
      case 3: ss << src.x << " " << src.y << " " << src.z;
      case 4: ss << src.x << " " << src.y << " " << src.z << " " << src.w;
    }

    target.AddMember(StringRef(name), s, alloc);
}