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api/basic_json/as_base_class/index.md

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+# 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`](https://json.nlohmann.me/api/basic_json/json_base_class_t/index.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`](https://json.nlohmann.me/api/basic_json/json_base_class_t/index.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`.
+
+```
+#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
+```
+
+## See also
+
+- [json_base_class_t](https://json.nlohmann.me/api/basic_json/json_base_class_t/index.md) - type of the custom base class
+
+## Version history
+
+- Added in version 3.13.0 unreleased.