NLOHMANN_JSON_FROM* macros not comptaible with non-default-constructible types

[RAnders00]

NLOHMANN_JSON_FROM* macros not comptaible with non-default-constructible types

[nlohmann]

This is documented behavior, see https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/#parameters

[RAnders00]

In this case, I need to use the adl_serializer specialization everywhere? I see. Thank you for the swift response, I had indeed overlooked this limitation.

Would you be open to tracking this deficiency as a feature request/request for enhancement then?

[nlohmann]

Would you be open to tracking this deficiency as a feature request/request for enhancement then?

Sure - though I hope it does not mean adding another dozen of macros for this case...

[gregmarr]

This works just fine, but now structs containing this type cannot be json-converted using the macros anymore:
Godbolt link: https://godbolt.org/z/q8oxq61sx (gcc trunk, nlohmann_json trunk)

That's simply because you didn't implement the version of from_json that takes the destination object by reference. You need that in order to support the get_to from the macros. Also, you should use the templated version of the first parameter so that you can also support ordered_json.

NLOHMANN_JSON_NAMESPACE_BEGIN
template <> struct adl_serializer<NonDefaultConstructible> {
    template<typename BasicJsonType>
    static void to_json(BasicJsonType &json_value, const NonDefaultConstructible &data) {
      json_value = data.get_inner_value();
    }

    template<typename BasicJsonType>
    static void from_json(BasicJsonType && j, NonDefaultConstructible &val) 
    {
      // There is no setter for this member, so I had to create a new one and move it into the original.
      // I assume in the original there is a setter, which would make this easier.
      val = NonDefaultConstructible{j.template get<std::string>()};
    }
};
NLOHMANN_JSON_NAMESPACE_END

@nlohmann It would probably be a good idea to update the docs examples to use the template BasicJsonType.

[RAnders00]

template<typename BasicJsonType>
static void from_json(BasicJsonType && j, NonDefaultConstructible &val) 

Just curious, why the forwarding reference? When I try it, it seems to work with a const BasicJsonType& too, and clangd gives me a warning that the forwarding reference is never forwarded inside the function body?

[gregmarr]

It should probably just be const&.