template specialization not deteced for third party type nested to STL containers

[aureliencc]

Hello everyone,

I'm using nlohmann json(which I love btw !) for a C++ project and I'm struggling to find the "good" way to convert a third party type when it is nested inside a STL container. wxString is converted to and from json successfully thanks to wxString adl_serializer specialization :

namespace nlohmann {
    template <>
    struct adl_serializer<wxString> {
        static void to_json(json& j, const wxString& str) {
            j = str.utf8_string();
        }

        static void from_json(const json& j, wxString& str) {
            str = wxString::FromUTF8(j.get<std::string>());
        }
    };
    ...

But when used inside std::vector<wxString>, it seems that the specialization is ignored ? I did not manage to get it called for my conversion, I had to wrote another specialization with the actual container to get it to work :

   template <>
    struct adl_serializer<std::vector<wxString>> {
        static void to_json(json& j, const std::vector<wxString>& str) {

            std::ranges::for_each(str,
                [&](const wxString& s) 
                { 
                    j.push_back(s.utf8_string());
                }
            );
        }

        static void from_json(const json& j, std::vector<wxString>& str) {

            std::ranges::for_each(j,
                [&](const std::string& s) 
                { 
                    str.push_back(wxString::FromUTF8(s));
                }
            );
        }
    };
};

Am I doing something wrong ? To my understanding, I should have only wrote the first specialization.

Thank you for your help,

[aureliencc]

Hello Mohammad,

Thank you for your reply.

I do think there is a visibility problem with my header containing the specialization because I did everything like you mentioned and still, it looks like the specialization is not "visible" when performing the conversion to nlohmann::json. What's weird is that adding the specialization std::vector<wxString> just below the wxString do the trick. I'll try to investigate further and come back to you.

[aureliencc]

So I tried to dig a bit further and I can confirm that, in my case, adl_serializer<wxString> isn't triggered by std::vector<wxString> :

This is so confusing to me because I did manage to get it working in a previous release. As it, this looks like an inclusion problem to me but the header(api/api.h) containing the specialization is present in all of the files so I really don't know how to solve this. Maybe it as something to do with the namespace and/or template of the serializer, I really don't know. I'm using #pragma once, tried with #ifndef but this did not solve the problem.

For now, I'm just going to keep struct adl_serializer<std::vector<wxString>> but I hope to find out what's wrong.

[aureliencc]

So... I created a new header file with ONLY the nlohmann json specialization and.... it worked.

Thank you,