examples/as_base_class.cpp

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

class base_class_with_hidden_members
{
  public:
    const char* type_name() const noexcept
    {
        return "my_type_name";
    }

    std::size_t size() const noexcept
    {
        return 42;
    }
};

using json = nlohmann::json::with_base_class_t<base_class_with_hidden_members>;

int main()
{
    json j = {1, 2, 3};

    // the members of basic_json hide the members of the base class
    std::cout << j.type_name() << ' ' << j.size() << '\n';

    // access the hidden members of the base class
    std::cout << j.as_base_class().type_name() << ' ' << j.as_base_class().size() << '\n';
}