deploy: 40a62947d3

api/macros/nlohmann_json_namespace_begin.md

@@ -14,7 +14,7 @@ These macros can be used to open and close the `nlohmann` namespace. See
 ## Default definition
 
 The default definitions open and close the `nlohmann` namespace. The precise definition of
-[`NLOHMANN_JSON_NAMESPACE_BEGIN`] varies as described [here](../../features/namespace.md#structure).
+`NLOHMANN_JSON_NAMESPACE_BEGIN` varies as described [here](../../features/namespace.md#structure).
 
 1. Default definition of `NLOHMANN_JSON_NAMESPACE_BEGIN`:
 
@@ -41,13 +41,47 @@ When these macros are not defined, the library will define them to their default
     [How do I convert third-party types?](../../features/arbitrary_types.md#how-do-i-convert-third-party-types) page.
 
     ```cpp
-    --8<-- "examples/nlohmann_json_namespace_begin.c++17.cpp"
+    #include <iostream>
+    #include <optional>
+    #include <nlohmann/json.hpp>
+    
+    // partial specialization (see https://json.nlohmann.me/features/arbitrary_types/)
+    NLOHMANN_JSON_NAMESPACE_BEGIN
+    template <typename T>
+    struct adl_serializer<std::optional<T>>
+    {
+        static void to_json(json& j, const std::optional<T>& opt)
+        {
+            if (opt == std::nullopt)
+            {
+                j = nullptr;
+            }
+            else
+            {
+                j = *opt;
+            }
+        }
+    };
+    NLOHMANN_JSON_NAMESPACE_END
+    
+    int main()
+    {
+        std::optional<int> o1 = 1;
+        std::optional<int> o2 = std::nullopt;
+    
+        NLOHMANN_JSON_NAMESPACE::json j;
+        j.push_back(o1);
+        j.push_back(o2);
+        std::cout << j << std::endl;
+    }
+    
     ```
     
     Output:
     
     ```json
-    --8<-- "examples/nlohmann_json_namespace_begin.c++17.output"
+    [1,null]
+    
     ```
 
 ## See also