How to parse a vector of objects with const attributes

[axx]

Hi,

I have this class:

class MyClass {
  public:
  const std::string _a;
  const std::string _b;
}

I then want to parse [{"a":"aaaaa", "b":"bbbbb"}] to a std::vector<MyClass>.
I tried using the to_json/from_json approach in but I can't because

void from_json(const json& j, MyClass& m) {
  m._a = j.at("a");   // error
 m._b = j.at("b");
}

The other approach using

MyClass from_json(const json& j) {
   return { j.at("a").get<std::string>(), j.at("b").get<std::string>() }
}

also doesn't work because of some requirements in std::vector.

Does someone have other ideas aside from just dropping the const in MyClass?

[theodelrieu]

Hello,

You technically could workaround that by specializing nlohmann::adl_serializer for MyClass.
Although it would not solve the std::vector problem (unless specializing nlohmann::adl_serializer<std::vector<MyClass>>, which is quite brittle especially if you want to support other containers).

I know that everytime I tried to use const member variables, I ended up removing const.
Since it prevents MoveAssignable and CopyAssignable, lots of containers will not work with it.

Removing const and using MyClass const& when needed seems better.

[axx]

Thanks for the ideas!