Generate template functions with NLOHMANN_DEFINE_TYPE macros (#4597)

kimci86 · web-flow · commit 8a882f32ed60 · 2025-01-18T22:59:09.000+01:00
* Support any basic_json type in NLOHMANN_DEFINE_TYPE_* macros

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Test NLOHMANN_DEFINE_TYPE_* macros also support unordered_json

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Simplify test about NLOHMANN_DEFINE_TYPE_ with many arguments

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Remove extra scope in macros tests

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Remove unused test class in macros tests

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Update documentation about NLOHMANN_DEFINE_TYPE_* macros

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Fix NLOHMANN_JSON_SERIALIZE_ENUM documentation

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Mark some variables const in macros tests, fixes clang-tidy

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Workaround clang 3.5 issue with const object initialization

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Update highlighted lines in NLOHMANN_DEFINE_TYPE_* macros examples

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Fix swapped macros in documentation

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Remove extra backslashes at the end of macros

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Require basic_json type in NLOHMANN_DEFINE_TYPE_* generated functions

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

* Fix typos in macros documentation

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;

---------

Signed-off-by: kimci86 &lt;kimci86@hotmail.fr&gt;
diff --git a/docs/mkdocs/docs/api/macros/nlohmann_define_derived_type.md b/docs/mkdocs/docs/api/macros/nlohmann_define_derived_type.md
@@ -64,21 +64,26 @@ Summary:
 Macros 1 and 2 add two friend functions to the class which take care of the serialization and deserialization:
 
 ```cpp
-friend void to_json(nlohmann::json&, const type&);
-friend void from_json(const nlohmann::json&, type&);
+template<typename BasicJsonType>
+friend void to_json(BasicJsonType&, const type&);
+template<typename BasicJsonType>
+friend void from_json(const BasicJsonType&, type&);
 ```
 
 Macros 4 and 5 add two functions to the namespace which take care of the serialization and deserialization:
 
 ```cpp
-void to_json(nlohmann::json&, const type&);
-void from_json(const nlohmann::json&, type&);
+template<typename BasicJsonType>
+void to_json(BasicJsonType&, const type&);
+template<typename BasicJsonType>
+void from_json(const BasicJsonType&, type&);
 ```
 
 Macros 3 and 6 add one function to the namespace which take care of the serialization only:
 
 ```cpp
-void to_json(nlohmann::json&, const type&);
+template<typename BasicJsonType>
+void to_json(BasicJsonType&, const type&);
 ```
 
 In first two cases, they call the `to_json`/`from_json` functions of the base type
@@ -88,12 +93,14 @@ before serializing/deserializing the members of the derived type:
 class A { /* ... */ };
 class B : public A { /* ... */ };
 
-void to_json(nlohmann::json& j, const B& b) {
+template<typename BasicJsonType>
+void to_json(BasicJsonType& j, const B& b) {
     nlohmann::to_json(j, static_cast<const A&>(b));
     // ...
 }
 
-void from_json(const nlohmann::json& j, B& b) {
+template<typename BasicJsonType>
+void from_json(const BasicJsonType& j, B& b) {
     nlohmann::from_json(j, static_cast<A&>(b));
     // ...
 }
@@ -105,7 +112,8 @@ In the third case, only `to_json` will be called:
 class A { /* ... */ };
 class B : public A { /* ... */ };
 
-void to_json(nlohmann::json& j, const B& b) {
+template<typename BasicJsonType>
+void to_json(BasicJsonType& j, const B& b) {
     nlohmann::to_json(j, static_cast<const A&>(b));
     // ...
 }
diff --git a/docs/mkdocs/docs/api/macros/nlohmann_define_type_intrusive.md b/docs/mkdocs/docs/api/macros/nlohmann_define_type_intrusive.md
@@ -40,8 +40,10 @@ Summary:
 The macros add two friend functions to the class which take care of the serialization and deserialization:
 
 ```cpp
-friend void to_json(nlohmann::json&, const type&);
-friend void from_json(const nlohmann::json&, type&); // except (3)
+template<typename BasicJsonType>
+friend void to_json(BasicJsonType&, const type&);
+template<typename BasicJsonType>
+friend void from_json(const BasicJsonType&, type&); // except (3)
 ```
 
 See examples below for the concrete generated code.
@@ -60,8 +62,6 @@ See examples below for the concrete generated code.
 
     - The current implementation is limited to at most 64 member variables. If you want to serialize/deserialize types
       with more than 64 member variables, you need to define the `to_json`/`from_json` functions manually.
-    - The macros only work for the [`nlohmann::json`](../json.md) type; other specializations such as
-      [`nlohmann::ordered_json`](../ordered_json.md) are currently unsupported.
 
 ## Examples
 
@@ -90,7 +90,7 @@ See examples below for the concrete generated code.
 
     The macro is equivalent to:
 
-    ```cpp hl_lines="22 23 24 25 26 27 28 29 30 31 32 33 34"
+    ```cpp hl_lines="22 23 24 25 26 27 28 29 30 31 32 33 34 35 36"
     --8<-- "examples/nlohmann_define_type_intrusive_explicit.cpp"
     ```
 
@@ -118,7 +118,7 @@ See examples below for the concrete generated code.
 
     The macro is equivalent to:
 
-    ```cpp hl_lines="22 23 24 25 26 27 28 29 30 31 32 33 34 35"
+    ```cpp hl_lines="22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37"
     --8<-- "examples/nlohmann_define_type_intrusive_with_default_explicit.cpp"
     ```
 
@@ -147,7 +147,7 @@ See examples below for the concrete generated code.
 
     The macro is equivalent to:
 
-    ```cpp hl_lines="22 22 23 24 25 26 27"
+    ```cpp hl_lines="22 22 23 24 25 26 27 28"
     --8<-- "examples/nlohmann_define_type_intrusive_only_serialize_explicit.cpp"
     ```
 
diff --git a/docs/mkdocs/docs/api/macros/nlohmann_define_type_non_intrusive.md b/docs/mkdocs/docs/api/macros/nlohmann_define_type_non_intrusive.md
@@ -40,8 +40,10 @@ Summary:
 The macros add two functions to the namespace which take care of the serialization and deserialization:
 
 ```cpp
-void to_json(nlohmann::json&, const type&);
-void from_json(const nlohmann::json&, type&); // except (3)
+template<typename BasicJsonType>
+void to_json(BasicJsonType&, const type&);
+template<typename BasicJsonType>
+void from_json(const BasicJsonType&, type&); // except (3)
 ```
 
 See examples below for the concrete generated code.
@@ -61,8 +63,6 @@ See examples below for the concrete generated code.
 
     - The current implementation is limited to at most 64 member variables. If you want to serialize/deserialize types
       with more than 64 member variables, you need to define the `to_json`/`from_json` functions manually.
-    - The macros only work for the [`nlohmann::json`](../json.md) type; other specializations such as
-      [`nlohmann::ordered_json`](../ordered_json.md) are currently unsupported.
 
 ## Examples
 
@@ -90,15 +90,15 @@ See examples below for the concrete generated code.
 
     The macro is equivalent to:
 
-    ```cpp hl_lines="16 17 18 19 20 21 22 23 24 25 26 27 28"
+    ```cpp hl_lines="16 17 18 19 20 21 22 23 24 25 26 27 28 29 30"
     --8<-- "examples/nlohmann_define_type_non_intrusive_explicit.cpp"
     ```
 
 ??? example "Example (2): NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT"
 
     Consider the following complete example:
 
-    ```cpp hl_lines="22"
+    ```cpp hl_lines="21"
     --8<-- "examples/nlohmann_define_type_non_intrusive_with_default_macro.cpp"
     ```
     
@@ -119,7 +119,7 @@ See examples below for the concrete generated code.
 
     The macro is equivalent to:
 
-    ```cpp hl_lines="22 23 24 25 26 27 28 29 30 31 32 33 34 35"
+    ```cpp hl_lines="21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36"
     --8<-- "examples/nlohmann_define_type_non_intrusive_with_default_explicit.cpp"
     ```
 
@@ -148,7 +148,7 @@ See examples below for the concrete generated code.
 
     The macro is equivalent to:
 
-    ```cpp hl_lines="16 17 18 19 20 21"
+    ```cpp hl_lines="16 17 18 19 20 21 22"
     --8<-- "examples/nlohmann_define_type_non_intrusive_only_serialize_explicit.cpp"
     ```
 
diff --git a/docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum.md b/docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum.md
@@ -20,7 +20,7 @@ The `NLOHMANN_JSON_SERIALIZE_ENUM` allows to define a user-defined serialization
 
 ## Default definition
 
-The macros add two friend functions to the class which take care of the serialization and deserialization:
+The macro adds two functions to the namespace which take care of the serialization and deserialization:
 
 ```cpp
 template<typename BasicJsonType>
diff --git a/docs/mkdocs/docs/examples/nlohmann_define_type_intrusive_explicit.cpp b/docs/mkdocs/docs/examples/nlohmann_define_type_intrusive_explicit.cpp
@@ -19,14 +19,16 @@ class person
         : name(std::move(name_)), address(std::move(address_)), age(age_)
     {}
 
-    friend void to_json(nlohmann::json& nlohmann_json_j, const person& nlohmann_json_t)
+    template<typename BasicJsonType>
+    friend void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
     {
         nlohmann_json_j["name"] = nlohmann_json_t.name;
         nlohmann_json_j["address"] = nlohmann_json_t.address;
         nlohmann_json_j["age"] = nlohmann_json_t.age;
     }
 
-    friend void from_json(const nlohmann::json& nlohmann_json_j, person& nlohmann_json_t)
+    template<typename BasicJsonType>
+    friend void from_json(const BasicJsonType& nlohmann_json_j, person& nlohmann_json_t)
     {
         nlohmann_json_t.name = nlohmann_json_j.at("name");
         nlohmann_json_t.address = nlohmann_json_j.at("address");
diff --git a/docs/mkdocs/docs/examples/nlohmann_define_type_intrusive_only_serialize_explicit.cpp b/docs/mkdocs/docs/examples/nlohmann_define_type_intrusive_only_serialize_explicit.cpp
@@ -19,7 +19,8 @@ class person
         : name(std::move(name_)), address(std::move(address_)), age(age_)
     {}
 
-    friend void to_json(nlohmann::json& nlohmann_json_j, const person& nlohmann_json_t)
+    template<typename BasicJsonType>
+    friend void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
     {
         nlohmann_json_j["name"] = nlohmann_json_t.name;
         nlohmann_json_j["address"] = nlohmann_json_t.address;
diff --git a/docs/mkdocs/docs/examples/nlohmann_define_type_intrusive_with_default_explicit.cpp b/docs/mkdocs/docs/examples/nlohmann_define_type_intrusive_with_default_explicit.cpp
@@ -19,14 +19,16 @@ class person
         : name(std::move(name_)), address(std::move(address_)), age(age_)
     {}
 
-    friend void to_json(nlohmann::json& nlohmann_json_j, const person& nlohmann_json_t)
+    template<typename BasicJsonType>
+    friend void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
     {
         nlohmann_json_j["name"] = nlohmann_json_t.name;
         nlohmann_json_j["address"] = nlohmann_json_t.address;
         nlohmann_json_j["age"] = nlohmann_json_t.age;
     }
 
-    friend void from_json(const nlohmann::json& nlohmann_json_j, person& nlohmann_json_t)
+    template<typename BasicJsonType>
+    friend void from_json(const BasicJsonType& nlohmann_json_j, person& nlohmann_json_t)
     {
         person nlohmann_json_default_obj;
         nlohmann_json_t.name = nlohmann_json_j.value("name", nlohmann_json_default_obj.name);
diff --git a/docs/mkdocs/docs/examples/nlohmann_define_type_non_intrusive_explicit.cpp b/docs/mkdocs/docs/examples/nlohmann_define_type_non_intrusive_explicit.cpp
@@ -13,14 +13,16 @@ struct person
     int age;
 };
 
-void to_json(nlohmann::json& nlohmann_json_j, const person& nlohmann_json_t)
+template<typename BasicJsonType>
+void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
 {
     nlohmann_json_j["name"] = nlohmann_json_t.name;
     nlohmann_json_j["address"] = nlohmann_json_t.address;
     nlohmann_json_j["age"] = nlohmann_json_t.age;
 }
 
-void from_json(const nlohmann::json& nlohmann_json_j, person& nlohmann_json_t)
+template<typename BasicJsonType>
+void from_json(const BasicJsonType& nlohmann_json_j, person& nlohmann_json_t)
 {
     nlohmann_json_t.name = nlohmann_json_j.at("name");
     nlohmann_json_t.address = nlohmann_json_j.at("address");
diff --git a/docs/mkdocs/docs/examples/nlohmann_define_type_non_intrusive_only_serialize_explicit.cpp b/docs/mkdocs/docs/examples/nlohmann_define_type_non_intrusive_only_serialize_explicit.cpp
@@ -13,7 +13,8 @@ struct person
     int age;
 };
 
-void to_json(nlohmann::json& nlohmann_json_j, const person& nlohmann_json_t)
+template<typename BasicJsonType>
+void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
 {
     nlohmann_json_j["name"] = nlohmann_json_t.name;
     nlohmann_json_j["address"] = nlohmann_json_t.address;
diff --git a/docs/mkdocs/docs/examples/nlohmann_define_type_non_intrusive_with_default_explicit.cpp b/docs/mkdocs/docs/examples/nlohmann_define_type_non_intrusive_with_default_explicit.cpp
@@ -18,14 +18,16 @@ struct person
     {}
 };
 
-void to_json(nlohmann::json& nlohmann_json_j, const person& nlohmann_json_t)
+template<typename BasicJsonType>
+void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
 {
     nlohmann_json_j["name"] = nlohmann_json_t.name;
     nlohmann_json_j["address"] = nlohmann_json_t.address;
     nlohmann_json_j["age"] = nlohmann_json_t.age;
 }
 
-void from_json(const nlohmann::json& nlohmann_json_j, person& nlohmann_json_t)
+template<typename BasicJsonType>
+void from_json(const BasicJsonType& nlohmann_json_j, person& nlohmann_json_t)
 {
     person nlohmann_json_default_obj;
     nlohmann_json_t.name = nlohmann_json_j.value("name", nlohmann_json_default_obj.name);
diff --git a/docs/mkdocs/docs/features/arbitrary_types.md b/docs/mkdocs/docs/features/arbitrary_types.md
@@ -89,10 +89,10 @@ There are six macros to make your life easier as long as you (1) want to use a J
 
 - [`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(name, member1, member2, ...)`](../api/macros/nlohmann_define_type_non_intrusive.md) is to be defined inside the namespace of the class/struct to create code for. It will throw an exception in `from_json()` due to a missing value in the JSON object.
 - [`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(name, member1, member2, ...)`](../api/macros/nlohmann_define_type_non_intrusive.md) is to be defined inside the namespace of the class/struct to create code for. It will not throw an exception in `from_json()` due to a missing value in the JSON object, but fills in values from object which is default-constructed by the type.
-- [`NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(name, member1, member2, ...)`](../api/macros/nlohmann_define_type_non_intrusive.md) is to be defined inside the namespace of the class/struct to create code for. It does not define a `fron_json()` function which is needed in case the type does not have a default constructor.
+- [`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(name, member1, member2, ...)`](../api/macros/nlohmann_define_type_non_intrusive.md) is to be defined inside the namespace of the class/struct to create code for. It does not define a `from_json()` function which is needed in case the type does not have a default constructor.
 - [`NLOHMANN_DEFINE_TYPE_INTRUSIVE(name, member1, member2, ...)`](../api/macros/nlohmann_define_type_intrusive.md) is to be defined inside the class/struct to create code for. This macro can also access private members. It will throw an exception in `from_json()` due to a missing value in the JSON object.
 - [`NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(name, member1, member2, ...)`](../api/macros/nlohmann_define_type_intrusive.md) is to be defined inside the class/struct to create code for. This macro can also access private members. It will not throw an exception in `from_json()` due to a missing value in the JSON object, but fills in values from object which is default-constructed by the type.
-- [`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(name, member1, member2, ...)`](../api/macros/nlohmann_define_type_intrusive.md) is to be defined inside the class/struct to create code for. This macro can also access private members. It does not define a `fron_json()` function which is needed in case the type does not have a default constructor.
+- [`NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(name, member1, member2, ...)`](../api/macros/nlohmann_define_type_intrusive.md) is to be defined inside the class/struct to create code for. This macro can also access private members. It does not define a `from_json()` function which is needed in case the type does not have a default constructor.
 
 Furthermore, there exist versions to use in case of derived classes:
 
@@ -120,8 +120,6 @@ For _derived_ classes and structs, use the following macros
 
     - The current macro implementations are limited to at most 64 member variables. If you want to serialize/deserialize
       types with more than 64 member variables, you need to define the `to_json`/`from_json` functions manually.
-    - The macros only work for the [`nlohmann::json`](../api/json.md) type; other specializations such as
-      [`nlohmann::ordered_json`](../api/ordered_json.md) are currently unsupported.
 
 ??? example
 
diff --git a/include/nlohmann/detail/macro_scope.hpp b/include/nlohmann/detail/macro_scope.hpp
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
diff --git a/tests/src/unit-udt_macro.cpp b/tests/src/unit-udt_macro.cpp

Original file line number	Diff line number	Diff line change
`@@ -19,14 +19,16 @@ class person`
`19`	`19`	`: name(std::move(name_)), address(std::move(address_)), age(age_)`
`20`	`20`	`{}`
`21`	`21`
`22`		`- friend void to_json(nlohmann::json& nlohmann_json_j, const person& nlohmann_json_t)`
	`22`	`+ template<typename BasicJsonType>`
	`23`	`+ friend void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)`
`23`	`24`	`{`
`24`	`25`	`nlohmann_json_j["name"] = nlohmann_json_t.name;`
`25`	`26`	`nlohmann_json_j["address"] = nlohmann_json_t.address;`
`26`	`27`	`nlohmann_json_j["age"] = nlohmann_json_t.age;`
`27`	`28`	`}`
`28`	`29`
`29`		`- friend void from_json(const nlohmann::json& nlohmann_json_j, person& nlohmann_json_t)`
	`30`	`+ template<typename BasicJsonType>`
	`31`	`+ friend void from_json(const BasicJsonType& nlohmann_json_j, person& nlohmann_json_t)`
`30`	`32`	`{`
`31`	`33`	`nlohmann_json_t.name = nlohmann_json_j.at("name");`
`32`	`34`	`nlohmann_json_t.address = nlohmann_json_j.at("address");`
Original file line number	Diff line number	Diff line change
`@@ -19,7 +19,8 @@ class person`
`19`	`19`	`: name(std::move(name_)), address(std::move(address_)), age(age_)`
`20`	`20`	`{}`
`21`	`21`
`22`		`- friend void to_json(nlohmann::json& nlohmann_json_j, const person& nlohmann_json_t)`
	`22`	`+ template<typename BasicJsonType>`
	`23`	`+ friend void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)`
`23`	`24`	`{`
`24`	`25`	`nlohmann_json_j["name"] = nlohmann_json_t.name;`
`25`	`26`	`nlohmann_json_j["address"] = nlohmann_json_t.address;`
Original file line number	Diff line number	Diff line change
`@@ -13,14 +13,16 @@ struct person`
`13`	`13`	`int age;`
`14`	`14`	`};`
`15`	`15`
`16`		`-void to_json(nlohmann::json& nlohmann_json_j, const person& nlohmann_json_t)`
	`16`	`+template<typename BasicJsonType>`
	`17`	`+void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)`
`17`	`18`	`{`
`18`	`19`	`nlohmann_json_j["name"] = nlohmann_json_t.name;`
`19`	`20`	`nlohmann_json_j["address"] = nlohmann_json_t.address;`
`20`	`21`	`nlohmann_json_j["age"] = nlohmann_json_t.age;`
`21`	`22`	`}`
`22`	`23`
`23`		`-void from_json(const nlohmann::json& nlohmann_json_j, person& nlohmann_json_t)`
	`24`	`+template<typename BasicJsonType>`
	`25`	`+void from_json(const BasicJsonType& nlohmann_json_j, person& nlohmann_json_t)`
`24`	`26`	`{`
`25`	`27`	`nlohmann_json_t.name = nlohmann_json_j.at("name");`
`26`	`28`	`nlohmann_json_t.address = nlohmann_json_j.at("address");`
Original file line number	Diff line number	Diff line change
`@@ -13,7 +13,8 @@ struct person`
`13`	`13`	`int age;`
`14`	`14`	`};`
`15`	`15`
`16`		`-void to_json(nlohmann::json& nlohmann_json_j, const person& nlohmann_json_t)`
	`16`	`+template<typename BasicJsonType>`
	`17`	`+void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)`
`17`	`18`	`{`
`18`	`19`	`nlohmann_json_j["name"] = nlohmann_json_t.name;`
`19`	`20`	`nlohmann_json_j["address"] = nlohmann_json_t.address;`
Original file line number	Diff line number	Diff line change
`@@ -18,14 +18,16 @@ struct person`
`18`	`18`	`{}`
`19`	`19`	`};`
`20`	`20`
`21`		`-void to_json(nlohmann::json& nlohmann_json_j, const person& nlohmann_json_t)`
	`21`	`+template<typename BasicJsonType>`
	`22`	`+void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)`
`22`	`23`	`{`
`23`	`24`	`nlohmann_json_j["name"] = nlohmann_json_t.name;`
`24`	`25`	`nlohmann_json_j["address"] = nlohmann_json_t.address;`
`25`	`26`	`nlohmann_json_j["age"] = nlohmann_json_t.age;`
`26`	`27`	`}`
`27`	`28`
`28`		`-void from_json(const nlohmann::json& nlohmann_json_j, person& nlohmann_json_t)`
	`29`	`+template<typename BasicJsonType>`
	`30`	`+void from_json(const BasicJsonType& nlohmann_json_j, person& nlohmann_json_t)`
`29`	`31`	`{`
`30`	`32`	`person nlohmann_json_default_obj;`
`31`	`33`	`nlohmann_json_t.name = nlohmann_json_j.value("name", nlohmann_json_default_obj.name);`