json/docs/examples/nlohmann_define_type_non_intrusive_with_default_explicit.cpp

#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

namespace ns
{
struct person
{
    std::string name = "John Doe";
    std::string address = "123 Fake St";
    int age = -1;

    person() = default;
    person(std::string name_, std::string address_, int age_)
        : name(std::move(name_)), address(std::move(address_)), age(age_)
    {}
};

void to_json(nlohmann::json& nlohmann_json_j, const person& nlohmann_json_t)
{
    nlohmann_json_j["name"] = nlohmann_json_t.name;
    nlohmann_json_j["address"] = nlohmann_json_t.address;
    nlohmann_json_j["age"] = nlohmann_json_t.age;
}

void from_json(const nlohmann::json& nlohmann_json_j, person& nlohmann_json_t)
{
    person nlohmann_json_default_obj;
    nlohmann_json_t.name = nlohmann_json_j.value("name", nlohmann_json_default_obj.name);
    nlohmann_json_t.address = nlohmann_json_j.value("address", nlohmann_json_default_obj.address);
    nlohmann_json_t.age = nlohmann_json_j.value("age", nlohmann_json_default_obj.age);
}
} // namespace ns

int main()
{
    ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};

    // serialization: person -> json
    json j = p;
    std::cout << "serialization: " << j << std::endl;

    // deserialization: json -> person
    json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
    auto p2 = j2.get<ns::person>();

    // incomplete deserialization:
    json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
    auto p3 = j3.get<ns::person>();
    std::cout << "roundtrip: " << json(p3) << std::endl;
}