Is it possible to decode a nullopt as null for optional fields in a struct?

[recsater]

Example

struct A {
  optional<int> a;
}
JSONCONS_N_MEMBER_TRAITS(A, 0, a)

int main() {
  std::string result;
  jsoncons::encode_json(A{}, result); // result -> "{}"
}

If result were { "a": null } with some option (like ignore_null: default true), it would have been better.

[danielaparker]

Either

JSONCONS_ALL_MEMBER_TRAITS(A, a) 

or

JSONCONS_N_MEMBER_TRAITS(A, 1, a)

would produce

{ "a": null }

But non-mandatory means that the member can be omitted.