Parsing JSON: no matching function for call to 'get_to(ns::Points&) const'

[activeshadow]

I have the following code I'm trying to get working:

namespace ns {

struct Point {
  std::string tag {};
  double value {};
};

typedef std::vector<Point> Points;

struct Status {
  Points measurements {};
};

void to_json(json& j, const Status& s) {
  for (const auto &p : s.measurements) {
    json point;

    point["tag"] = p.tag;
    point["value"] = p.value;

    j["measurements"].push_back(point);
  }
}

void from_json(const json& j, Status& s) {
  j.at("measurements").get_to(s.measurements);
}

void to_json(json& j, const Point& p) {
  j["tag"] = p.tag;
  j["value"] = p.value;
}

void from_json(const json& j, Point& p) {
  j.at("tag").get_to(p.tag);
  j.at("value").get_to(p.value);
}

}

When I try to compile this, I get the following error output:

envelope.hpp: In function 'void ns::from_json(const json&, ns::Status&)':
envelope.hpp:97:45: error: no matching function for call to 'nlohmann::basic_json<>::get_to(ns::Points&) const'
   97 |   j.at("measurements").get_to(s.measurements);
      |                                             ^
In file included from envelope.hpp:8,
/deps/json/single_include/nlohmann/json.hpp:18952:17: note: candidate: 'template<class ValueType, typename std::enable_if<((! nlohmann::detail::is_basic_json<BasicJsonType>::value) && nlohmann::detail::has_from_json<nlohmann::basic_json<>, ValueType, void>::value), int>::type <anonymous> > ValueType& nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>::get_to(ValueType&) const [with ValueType = ValueType; typename std::enable_if<((! nlohmann::detail::is_basic_json<BasicJsonType>::value) && nlohmann::detail::has_from_json<nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>, ValueType>::value), int>::type <anonymous> = <enumerator>; ObjectType = std::map; ArrayType = std::vector; StringType = std::__cxx11::basic_string<char>; BooleanType = bool; NumberIntegerType = long int; NumberUnsignedType = long unsigned int; NumberFloatType = double; AllocatorType = std::allocator; JSONSerializer = nlohmann::adl_serializer; BinaryType = std::vector<unsigned char>]'
18952 |     ValueType & get_to(ValueType& v) const noexcept(noexcept(
      |                 ^~~~~~
/deps/json/single_include/nlohmann/json.hpp:18952:17: note:   template argument deduction/substitution failed:
/deps/json/single_include/nlohmann/json.hpp:18951:28: error: no type named 'type' in 'struct std::enable_if<false, int>'
18951 |                    int > = 0 >
      |                            ^
/deps/json/single_include/nlohmann/json.hpp:18965:17: note: candidate: 'template<class ValueType, typename std::enable_if<nlohmann::detail::is_basic_json<BasicJsonType>::value, int>::type <anonymous> > ValueType& nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>::get_to(ValueType&) const [with ValueType = ValueType; typename std::enable_if<nlohmann::detail::is_basic_json<BasicJsonType>::value, int>::type <anonymous> = <enumerator>; ObjectType = std::map; ArrayType = std::vector; StringType = std::__cxx11::basic_string<char>; BooleanType = bool; NumberIntegerType = long int; NumberUnsignedType = long unsigned int; NumberFloatType = double; AllocatorType = std::allocator; JSONSerializer = nlohmann::adl_serializer; BinaryType = std::vector<unsigned char>]'
18965 |     ValueType & get_to(ValueType& v) const
      |                 ^~~~~~
/deps/json/single_include/nlohmann/json.hpp:18965:17: note:   template argument deduction/substitution failed:
/deps/json/single_include/nlohmann/json.hpp:18964:25: error: no type named 'type' in 'struct std::enable_if<false, int>'
18964 |                  int> = 0>
      |                         ^
/deps/json/single_include/nlohmann/json.hpp:18976:11: note: candidate: 'template<class T, long unsigned int N, class Array, typename std::enable_if<nlohmann::detail::has_from_json<nlohmann::basic_json<>, Array, void>::value, int>::type <anonymous> > Array nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>::get_to(T (&)[N]) const [with T = T; long unsigned int N = N; Array = Array; typename std::enable_if<nlohmann::detail::has_from_json<nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>, Array>::value, int>::type <anonymous> = <enumerator>; ObjectType = std::map; ArrayType = std::vector; StringType = std::__cxx11::basic_string<char>; BooleanType = bool; NumberIntegerType = long int; NumberUnsignedType = long unsigned int; NumberFloatType = double; AllocatorType = std::allocator; JSONSerializer = nlohmann::adl_serializer; BinaryType = std::vector<unsigned char>]'
18976 |     Array get_to(T (&v)[N]) const // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
      |           ^~~~~~
/deps/json/single_include/nlohmann/json.hpp:18976:11: note:   template argument deduction/substitution failed:
envelope.hpp:97:45: note:   mismatched types 'T [N]' and 'ns::Points' {aka 'std::vector<ns::Point>'}
   97 |   j.at("measurements").get_to(s.measurements);
      |                                             ^

Any chance someone can tell me what I'm doing wrong here? It looks like it's an issue w/ a vector containing a custom struct, but I can't figure out why.

Thanks in advance!

[glattercj]

Move your Point to_json/from_json functions before the Status functions, then it should be good.

[activeshadow]

Oof... thanks @glattercj! That did the trick. 👍