api/basic_json/as_base_class.md

# <small>nlohmann::basic_json::</small>as_base_class

```cpp
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`](json_base_class_t.md). 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`](json_base_class_t.md)

## 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`.
    
    ```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';
    }
    
    ```
    
    Output:
    
    ```json
    array 3
    my_type_name 42
    
    ```

## See also

- [`json_base_class_t`](json_base_class_t.md) - type of the custom base class
- [Template Parameter Requirements](../../features/types/template_parameters.md) - requirements on the `CustomBaseClass` template parameter

## Version history

- Added in version 3.13.0.