nlohmann::basic_json::as_base_class¶

json_base_class_t& as_base_class() noexcept;
const json_base_class_t& as_base_class() const noexcept;

Returns a reference to this object as its custom base class json_base_class_t. No copy is made.

Since basic_json derives from json_base_class_t, a member of basic_json hides any member of the custom base class with the same name. This function makes such hidden members accessible again.

Return value¶

reference to this object as json_base_class_t

Exception safety¶

No-throw guarantee: this function never throws exceptions.

Complexity¶

Constant.

Notes¶

The function is equivalent to static_cast<json_base_class_t&>(j) (or static_cast<const json_base_class_t&>(j)).

Examples¶

Example

The example shows how to use as_base_class to access members of the custom base class that are hidden by members of basic_json.

#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::basic_json <
             std::map,
             std::vector,
             std::string,
             bool,
             std::int64_t,
             std::uint64_t,
             double,
             std::allocator,
             nlohmann::adl_serializer,
             std::vector<std::uint8_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';
}

Output:

array 3
my_type_name 42

Version history¶

Added in version 3.13.0 unreleased.