NaN values about json_dto

[eao197]

Hi! Thanks for reporting that. I'll take a look.

[eao197]

Values like "nan", "inf" and "-inf" are non-standard in JSON. They can be used as non-standard extensions and RapidJson handles them that way:

• a flag rapidjson::kParseNanAndInfFlag should be passed to from_json function, for example:

const auto my_data = json_dto::from_json<MyData, rapidjson::kParseNanAndInfFlag>(str);

• RapidJSON recognizes only values NaN, Inf, or Infinitiy. Not nan, Nan, inf or something else. Not "NaN" nor "nan", nor "Nan". It means that {"id":234, "test":"Nan"} can't be parsed by RapidJSON. Only in that form: {"id":234, "test":NaN}.

Because json_dto is just a thin wrapper around RapidJSON it's impossible to parse documents like {"id":234, "test":"Nan"} by json_dto.

However, json_dto can be extended by something like:

struct MyData {
  int id;
  double test;
  ...
  template<typename Io>
  void json_io(Io & io) {
     io & json_dto::mandatory("id", id)
        & json_dto::mandatory(double_extractor{}, "test", test);
  }
};

where double_extractor will be something like:

struct double_extractor {
  double read(const rapidjson::Value & from) const {
     if(from.IsNumber()) return from.GetDouble();
     if(from.IsString()) {
        const auto * str_v = from.GetString();
        if(0 == strcasecmp(str_v, "nan")) return std::numeric_limits<double>::quiet_NaN();
        ...
     }
     throw json_dto::ex_t{"value is not double"};
  }
  void write(double v, rapidjson::Value & to, rapidjson::MemoryPoolAllocator<> &) const {
    to.SetDouble(v);
  }
};

and you have to write such double_extractor by yourself.

[eao197]

@qwertynat
Version 0.2.10 with support of custom Reader_Writer types (from an idea described above) is just released. Now you can try to handle non-standard values in JSON document via your Reader_Writer as described here.

[qwertynat]

niceone! will have a play with it.