How to Serialize/Deserialize Arbitrary Types

[Lunar2kPS]

I'm coming from primarily a Unity/C# background, trying to learn C++.
I'm trying to integrate GLM and my own custom types, and potentially types from other C++ libraries that I'm gonna add into my project, with JSON support from this library.

I read from the docs that I needa define my own adl_serializer to handle to/from JSON from a given type, using templates.
How do I call this though?

#include <iostream>
#include <fstream>

#include "nlohmann/json.hpp"
#include "glm/glm.hpp"

using std::cout;
using std::endl;
using std::getline;

using std::ifstream;

using json = nlohmann::json;
using glm::vec3;

NLOHMANN_JSON_NAMESPACE_BEGIN
template <typename T>
struct adl_serializer {
    static void to_json(json& j, const vec& value) {
        j = json({
            {"x", value.x},
            {"y", value.y},
            {"z", value.z}
        });
    }
    
    static void from_json(const json& j, vec3& value) {
        j.at("x").get_to(value.x);
        j.at("y").get_to(value.y);
        j.at("z").get_to(value.z);
    }
};
NLOHMANN_JSON_NAMESPACE_END

void testJSON() {
    cout << "JSON testing..." << endl;
    
    vec3 position = vec3(2, -9, 6);
    json jPosition = position; //ERROR: no suitable user-defined conversion from "glm::vec3" to "json" existsC/C++(312)
    
    cout << jPosition.dump(4) << endl;
    cout << endl;
}

I just get an error that I can't convert from vec3 to json, in this example.

[nlohmann]

You need no define the serializer inside the glm namespace.

[Lunar2kPS]

Ah gotcha, I probably need to learn more about templates too 😅 but I got this working!
Thanks for your time :)

So the difference (that matters) here is this:

- template <typename T>
- struct adl_serializer {
+ template <>
+ struct adl_serializer<vec3> {

Again, I gotta learn templates here (cause I know C# generics, but not C++ templates), but I think this is the right syntax to provide a specialization of their adl_serializer type for GLM's vec3 type. Mostly just syntax.

It worked either way, either by using the macros (NLOHMANN_JSON_NAMESPACE_BEGIN, etc.) or manually defining my adl_serializer inside namespace nlohmann { ... }.

Here's the full code for reference:

#include <iostream>
#include <fstream>

#include "nlohmann/json.hpp"
#include "glm/glm.hpp"

using std::cout;
using std::endl;
using std::getline;

using std::ifstream;

using json = nlohmann::json;
using glm::vec3;

namespace nlohmann {
    template <>
    struct adl_serializer<vec3> {
        static void to_json(json& j, const vec3& value) {
            j = json({
                {"x", value.x},
                {"y", value.y},
                {"z", value.z}
            });
        }
        
        static void from_json(const json& j, vec3& value) {
            j.at("x").get_to(value.x);
            j.at("y").get_to(value.y);
            j.at("z").get_to(value.z);
        }
    };
}

void testJSON() {
    cout << "JSON testing..." << endl;
    
    vec3 position = vec3(2, -9, 6);
    json jPosition = position; //ERROR: no suitable user-defined conversion from "glm::vec3" to "json" existsC/C++(312)

    cout << jPosition.dump(4) << endl;
    cout << endl;
}