Add ONLY_SERIALIZE for NLOHMANN_DEFINE_DERIVED_TYPE_* macros (#4562)

docs/mkdocs/docs/api/macros/nlohmann_define_derived_type.md

@@ -1,20 +1,23 @@
 <h1>NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT,
-    NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT</h1>
+    NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE,
+    NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</h1>
 
 ```cpp
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(type, base_type, member...)                  // (1)
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(type, base_type, member...)                    // (1)
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(type, base_type, member...)     // (2)
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(type, base_type, member...)       // (2)
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(type, base_type, member...)     // (3)
 
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(type, base_type, member...)              // (3)
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(type, base_type, member...)                // (4)
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(type, base_type, member...) // (4)
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(type, base_type, member...)   // (5)
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(type, base_type, member...) // (6)
 ```
 
 These macros can be used to simplify the serialization/deserialization of derived types if you want to use a JSON
 object as serialization and want to use the member variable names as object keys in that object.
 
-- Macros 1 and 2 are to be defined **inside** the class/struct to create code for.
+- Macros 1, 2 and 3 are to be defined **inside** the class/struct to create code for.
 Like [`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](nlohmann_define_type_intrusive.md), they can access private members.
-- Macros 3 and 4 are to be defined **outside** the class/struct to create code for, but **inside** its namespace.
+- Macros 4, 5 and 6 are to be defined **outside** the class/struct to create code for, but **inside** its namespace.
 Like [`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`](nlohmann_define_type_non_intrusive.md),
 they **cannot** access private members.
 
@@ -48,14 +51,20 @@ friend void to_json(nlohmann::json&, const type&);
 friend void from_json(const nlohmann::json&, type&);
 ```
 
-Macros 3 and 4 add two functions to the namespace which take care of the serialization and deserialization:
+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&);
 ```
 
-In both cases they call the `to_json`/`from_json` functions of the base 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&);
+```
+
+In first two cases cases they call the `to_json`/`from_json` functions of the base type
 before serializing/deserializing the members of the derived type:
 
 ```cpp
@@ -73,12 +82,24 @@ void from_json(const nlohmann::json& j, B& b) {
 }
 ```
 
+In the third case only `to_json` will be called:
+
+```cpp
+class A { /* ... */ };
+class B : public A { /* ... */ };
+
+void to_json(nlohmann::json& j, const B& b) {
+    nlohmann::to_json(j, static_cast<const A&>(b));
+    // ...
+}
+```
+
 ## Notes
 
 !!! info "Prerequisites"
 
-    - Macros 1 and 2 have the same prerequisites of NLOHMANN_DEFINE_TYPE_INTRUSIVE. 
+    - Macros 1, 2 and 3 have the same prerequisites of NLOHMANN_DEFINE_TYPE_INTRUSIVE. 
-    - Macros 3 and 3 have the same prerequisites of NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE.
+    - Macros 4, 5 and 6 have the same prerequisites of NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE.
     - Serialization/deserialization of base types must be defined.
 
 !!! warning "Implementation limits"

docs/mkdocs/docs/features/macros.md

@@ -102,8 +102,10 @@ See [full documentation of `JSON_USE_IMPLICIT_CONVERSIONS`](../api/macros/json_u
 
 ## `NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(type, base_type, member...)`
 ## `NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(type, base_type, member...)`
+## `NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(type, base_type, member...)`
 ## `NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(type, base_type, member...)`
 ## `NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(type, base_type, member...)`
+## `NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(type, base_type, member...)`
 
 ## `NLOHMANN_DEFINE_TYPE_INTRUSIVE(type, member...)`
 

docs/mkdocs/mkdocs.yml

@@ -287,8 +287,10 @@ nav:
         - 'JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON': api/macros/json_use_legacy_discarded_value_comparison.md
         - 'NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE': api/macros/nlohmann_define_derived_type.md
         - 'NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT': api/macros/nlohmann_define_derived_type.md
+        - 'NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_derived_type.md
         - 'NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE': api/macros/nlohmann_define_derived_type.md
         - 'NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT': api/macros/nlohmann_define_derived_type.md
+        - 'NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_derived_type.md
         - 'NLOHMANN_DEFINE_TYPE_INTRUSIVE': api/macros/nlohmann_define_type_intrusive.md
         - 'NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT': api/macros/nlohmann_define_type_intrusive.md
         - 'NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE': api/macros/nlohmann_define_type_non_intrusive.md

include/nlohmann/detail/macro_scope.hpp

@@ -442,6 +442,9 @@
     friend void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
     friend void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) }
 
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(Type, BaseType, ...)  \
+    friend void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+
 /*!
 @brief macro
 @def NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE
@@ -455,6 +458,9 @@
     inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
     inline void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) }
 
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(Type, BaseType, ...)  \
+    inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+
 // inspired from https://stackoverflow.com/a/26745591
 // allows to call any std function as if (e.g. with begin):
 // using std::begin; begin(x);

single_include/nlohmann/json.hpp

@@ -2809,6 +2809,9 @@ JSON_HEDLEY_DIAGNOSTIC_POP
     friend void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
     friend void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) }
 
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(Type, BaseType, ...)  \
+    friend void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+
 /*!
 @brief macro
 @def NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE
@@ -2822,6 +2825,9 @@ JSON_HEDLEY_DIAGNOSTIC_POP
     inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
     inline void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) }
 
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(Type, BaseType, ...)  \
+    inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+
 // inspired from https://stackoverflow.com/a/26745591
 // allows to call any std function as if (e.g. with begin):
 // using std::begin; begin(x);

tests/src/unit-udt_macro.cpp

@@ -440,6 +440,32 @@ class person_without_default_constructor_2
 
 NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(person_without_default_constructor_2, name, age)
 
+class derived_person_only_serialize_public : public person_without_default_constructor_1
+{
+  public:
+    std::string hair_color;
+
+    derived_person_only_serialize_public(std::string name_, int age_, std::string hair_color_)
+        : person_without_default_constructor_1(std::move(name_), age_)
+        , hair_color(std::move(hair_color_))
+    {}
+};
+
+NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(derived_person_only_serialize_public, person_without_default_constructor_1, hair_color)
+
+class derived_person_only_serialize_private : person_without_default_constructor_1
+{
+  private:
+    std::string hair_color;
+  public:
+    derived_person_only_serialize_private(std::string name_, int age_, std::string hair_color_)
+        : person_without_default_constructor_1(std::move(name_), age_)
+        , hair_color(std::move(hair_color_))
+    {}
+
+    NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(derived_person_only_serialize_private, person_without_default_constructor_1, hair_color)
+};
+
 } // namespace persons
 
 TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRUSIVE and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE", T, // NOLINT(readability-math-missing-parentheses)
@@ -657,3 +683,25 @@ TEST_CASE_TEMPLATE("Serialization of non-default-constructible classes via NLOHM
         }
     }
 }
+
+TEST_CASE_TEMPLATE("Serialization of non-default-constructible classes via NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE and NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE", T, // NOLINT(readability-math-missing-parentheses)
+                   persons::derived_person_only_serialize_public,
+                   persons::derived_person_only_serialize_private)
+{
+    SECTION("derived person only serialize")
+    {
+        {
+            // serialization of a single object
+            T person{"Erik", 1, "brown"};
+            CHECK(json(person).dump() == "{\"age\":1,\"hair_color\":\"brown\",\"name\":\"Erik\"}");
+
+            // serialization of a container with objects
+            std::vector<T> const two_persons
+            {
+                {"Erik", 1, "brown"},
+                {"Kyle", 2, "black"}
+            };
+            CHECK(json(two_persons).dump() == "[{\"age\":1,\"hair_color\":\"brown\",\"name\":\"Erik\"},{\"age\":2,\"hair_color\":\"black\",\"name\":\"Kyle\"}]");
+        }
+    }
+}