Merge pull request #2225 from nlohmann/issue2175

Simplify conversion from/to custom types

README.md

@@ -869,6 +869,42 @@ Some important things:
 * In function `from_json`, use function [`at()`](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a93403e803947b86f4da2d1fb3345cf2c.html#a93403e803947b86f4da2d1fb3345cf2c) to access the object values rather than `operator[]`. In case a key does not exist, `at` throws an exception that you can handle, whereas `operator[]` exhibits undefined behavior.
 * You do not need to add serializers or deserializers for STL types like `std::vector`: the library already implements these.
 
+#### Simplify your life with macros
+
+If you just want to serialize/deserialize some structs, the `to_json`/`from_json` functions can be a lot of boilerplate.
+
+There are two macros to make your life easier as long as you (1) want to use a JSON object as serialization and (2) want to use the member variable names as object keys in that object:
+
+- `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(name, member1, member2, ...)` is to be defined inside of the namespace of the class/struct to create code for.
+- `NLOHMANN_DEFINE_TYPE_INTRUSIVE(name, member1, member2, ...)` is to be defined inside of the class/struct to create code for. This macro can also access private members.
+
+In both macros, the first parameter is the name of the class/struct, and all remaining parameters name the members.
+
+##### Examples
+
+The `to_json`/`from_json` functions for the `person` struct above can be created with:
+
+```cpp
+namespace ns {
+    NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(person, name, address, age);
+}
+```
+
+Here is an example with private members, where `NLOHMANN_DEFINE_TYPE_INTRUSIVE` is needed:
+
+```cpp
+namespace ns {
+    class address {
+      private:
+        std::string street;
+        int housenumber;
+        int postcode;
+        
+      public:
+        NLOHMANN_DEFINE_TYPE_INTRUSIVE(address, street, housenumber, postcode);
+    };
+}
+```
 
 #### How do I convert third-party types?
 

include/nlohmann/detail/macro_scope.hpp

@@ -124,3 +124,44 @@
     basic_json<ObjectType, ArrayType, StringType, BooleanType,             \
     NumberIntegerType, NumberUnsignedType, NumberFloatType,                \
     AllocatorType, JSONSerializer, BinaryType>
+
+// Macros to simplify conversion from/to types
+
+#define NLOHMANN_JSON_EXPAND( x ) x
+#define NLOHMANN_JSON_GET_MACRO(_1,_2,_3,_4,_5,_6, _7, _8, _9, _10, _11, NAME,...) NAME
+
+#define NLOHMANN_JSON_PASTE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_GET_MACRO(__VA_ARGS__, NLOHMANN_JSON_PASTE11, \
+        NLOHMANN_JSON_PASTE10, NLOHMANN_JSON_PASTE9, NLOHMANN_JSON_PASTE8, NLOHMANN_JSON_PASTE7, \
+        NLOHMANN_JSON_PASTE6, NLOHMANN_JSON_PASTE5, NLOHMANN_JSON_PASTE4, NLOHMANN_JSON_PASTE3, \
+        NLOHMANN_JSON_PASTE2, NLOHMANN_JSON_PASTE1)(__VA_ARGS__))
+#define NLOHMANN_JSON_PASTE2(func,  v1)                                      func(v1)
+#define NLOHMANN_JSON_PASTE3(func,  v1, v2)                                  NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE2(func, v2)
+#define NLOHMANN_JSON_PASTE4(func,  v1, v2, v3)                              NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE3(func, v2, v3)
+#define NLOHMANN_JSON_PASTE5(func,  v1, v2, v3, v4)                          NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE4(func, v2, v3, v4)
+#define NLOHMANN_JSON_PASTE6(func,  v1, v2, v3, v4, v5)                      NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE5(func, v2, v3, v4, v5)
+#define NLOHMANN_JSON_PASTE7(func,  v1, v2, v3, v4, v5, v6)                  NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE6(func, v2, v3, v4, v5, v6)
+#define NLOHMANN_JSON_PASTE8(func,  v1, v2, v3, v4, v5, v6, v7)              NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE7(func, v2, v3, v4, v5, v6, v7)
+#define NLOHMANN_JSON_PASTE9(func,  v1, v2, v3, v4, v5, v6, v7, v8)          NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE8(func, v2, v3, v4, v5, v6, v7, v8)
+#define NLOHMANN_JSON_PASTE10(func, v1, v2, v3, v4, v5, v6, v7, v8, v9)      NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE8(func, v2, v3, v4, v5, v6, v7, v8, v9)
+#define NLOHMANN_JSON_PASTE11(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE8(func, v2, v3, v4, v5, v6, v7, v8, v9, v10)
+
+#define NLOHMANN_JSON_TO(v1) j[#v1] = t.v1;
+#define NLOHMANN_JSON_FROM(v1) j.at(#v1).get_to(t.v1);
+
+/*!
+@brief macro
+@def NLOHMANN_DEFINE_TYPE_INTRUSIVE
+@since version 3.9.0
+*/
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type, ...)  \
+    friend void to_json(nlohmann::json& j, const Type& t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+    friend void from_json(const nlohmann::json& j, Type& t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) }
+
+/*!
+@brief macro
+@def NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE
+@since version 3.9.0
+*/
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(Type, ...)  \
+    void to_json(nlohmann::json& j, const Type& t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+    void from_json(const nlohmann::json& j, Type& t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) }

single_include/nlohmann/json.hpp

@@ -2153,6 +2153,47 @@ JSON_HEDLEY_DIAGNOSTIC_POP
     NumberIntegerType, NumberUnsignedType, NumberFloatType,                \
     AllocatorType, JSONSerializer, BinaryType>
 
+// Macros to simplify conversion from/to types
+
+#define NLOHMANN_JSON_EXPAND( x ) x
+#define NLOHMANN_JSON_GET_MACRO(_1,_2,_3,_4,_5,_6, _7, _8, _9, _10, _11, NAME,...) NAME
+
+#define NLOHMANN_JSON_PASTE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_GET_MACRO(__VA_ARGS__, NLOHMANN_JSON_PASTE11, \
+        NLOHMANN_JSON_PASTE10, NLOHMANN_JSON_PASTE9, NLOHMANN_JSON_PASTE8, NLOHMANN_JSON_PASTE7, \
+        NLOHMANN_JSON_PASTE6, NLOHMANN_JSON_PASTE5, NLOHMANN_JSON_PASTE4, NLOHMANN_JSON_PASTE3, \
+        NLOHMANN_JSON_PASTE2, NLOHMANN_JSON_PASTE1)(__VA_ARGS__))
+#define NLOHMANN_JSON_PASTE2(func,  v1)                                      func(v1)
+#define NLOHMANN_JSON_PASTE3(func,  v1, v2)                                  NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE2(func, v2)
+#define NLOHMANN_JSON_PASTE4(func,  v1, v2, v3)                              NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE3(func, v2, v3)
+#define NLOHMANN_JSON_PASTE5(func,  v1, v2, v3, v4)                          NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE4(func, v2, v3, v4)
+#define NLOHMANN_JSON_PASTE6(func,  v1, v2, v3, v4, v5)                      NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE5(func, v2, v3, v4, v5)
+#define NLOHMANN_JSON_PASTE7(func,  v1, v2, v3, v4, v5, v6)                  NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE6(func, v2, v3, v4, v5, v6)
+#define NLOHMANN_JSON_PASTE8(func,  v1, v2, v3, v4, v5, v6, v7)              NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE7(func, v2, v3, v4, v5, v6, v7)
+#define NLOHMANN_JSON_PASTE9(func,  v1, v2, v3, v4, v5, v6, v7, v8)          NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE8(func, v2, v3, v4, v5, v6, v7, v8)
+#define NLOHMANN_JSON_PASTE10(func, v1, v2, v3, v4, v5, v6, v7, v8, v9)      NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE8(func, v2, v3, v4, v5, v6, v7, v8, v9)
+#define NLOHMANN_JSON_PASTE11(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE8(func, v2, v3, v4, v5, v6, v7, v8, v9, v10)
+
+#define NLOHMANN_JSON_TO(v1) j[#v1] = t.v1;
+#define NLOHMANN_JSON_FROM(v1) j.at(#v1).get_to(t.v1);
+
+/*!
+@brief macro
+@def NLOHMANN_DEFINE_TYPE_INTRUSIVE
+@since version 3.9.0
+*/
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type, ...)  \
+    friend void to_json(nlohmann::json& j, const Type& t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+    friend void from_json(const nlohmann::json& j, Type& t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) }
+
+/*!
+@brief macro
+@def NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE
+@since version 3.9.0
+*/
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(Type, ...)  \
+    void to_json(nlohmann::json& j, const Type& t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+    void from_json(const nlohmann::json& j, Type& t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) }
+
 
 namespace nlohmann
 {

test/CMakeLists.txt

@@ -132,6 +132,7 @@ set(files
     src/unit-to_chars.cpp
     src/unit-ubjson.cpp
     src/unit-udt.cpp
+    src/unit-udt_macro.cpp
     src/unit-unicode.cpp
     src/unit-user_defined_input.cpp
     src/unit-wstring.cpp)

test/src/unit-udt_macro.cpp

@@ -0,0 +1,126 @@
+/*
+    __ _____ _____ _____
+ __|  |   __|     |   | |  JSON for Modern C++ (test suite)
+|  |  |__   |  |  | | | |  version 3.8.0
+|_____|_____|_____|_|___|  https://github.com/nlohmann/json
+
+Licensed under the MIT License <http://opensource.org/licenses/MIT>.
+SPDX-License-Identifier: MIT
+Copyright (c) 2013-2019 Niels Lohmann <http://nlohmann.me>.
+
+Permission is hereby  granted, free of charge, to any  person obtaining a copy
+of this software and associated  documentation files (the "Software"), to deal
+in the Software  without restriction, including without  limitation the rights
+to  use, copy,  modify, merge,  publish, distribute,  sublicense, and/or  sell
+copies  of  the Software,  and  to  permit persons  to  whom  the Software  is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE  IS PROVIDED "AS  IS", WITHOUT WARRANTY  OF ANY KIND,  EXPRESS OR
+IMPLIED,  INCLUDING BUT  NOT  LIMITED TO  THE  WARRANTIES OF  MERCHANTABILITY,
+FITNESS FOR  A PARTICULAR PURPOSE AND  NONINFRINGEMENT. IN NO EVENT  SHALL THE
+AUTHORS  OR COPYRIGHT  HOLDERS  BE  LIABLE FOR  ANY  CLAIM,  DAMAGES OR  OTHER
+LIABILITY, WHETHER IN AN ACTION OF  CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE  OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+#include <utility>
+
+namespace persons
+{
+class person_with_private_data
+{
+  private:
+    std::string name;
+    int age = 0;
+
+  public:
+    bool operator==(const person_with_private_data& rhs) const
+    {
+        return std::tie(name, age) == std::tie(rhs.name, rhs.age);
+    }
+
+    person_with_private_data() = default;
+    person_with_private_data(std::string name, int age)
+        : name(std::move(name))
+        , age(age)
+    {}
+
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE(person_with_private_data, age, name);
+};
+
+class person_without_private_data_1
+{
+  public:
+    std::string name;
+    int age = 0;
+
+    bool operator==(const person_without_private_data_1& rhs) const
+    {
+        return std::tie(name, age) == std::tie(rhs.name, rhs.age);
+    }
+
+    person_without_private_data_1() = default;
+    person_without_private_data_1(std::string name, int age)
+        : name(std::move(name))
+        , age(age)
+    {}
+
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE(person_without_private_data_1, age, name);
+};
+
+class person_without_private_data_2
+{
+  public:
+    std::string name;
+    int age = 0;
+
+    bool operator==(const person_without_private_data_2& rhs) const
+    {
+        return std::tie(name, age) == std::tie(rhs.name, rhs.age);
+    }
+
+    person_without_private_data_2() = default;
+    person_without_private_data_2(std::string name, int age)
+        : name(std::move(name))
+        , age(age)
+    {}
+};
+
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(person_without_private_data_2, age, name);
+} // namespace persons
+
+TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRUSIVE", T,
+                   persons::person_with_private_data,
+                   persons::person_without_private_data_1,
+                   persons::person_without_private_data_2)
+{
+    SECTION("person")
+    {
+        // serialization
+        T p1("Erik", 1);
+        CHECK(json(p1).dump() == "{\"age\":1,\"name\":\"Erik\"}");
+
+        // deserialization
+        T p2 = json(p1);
+        CHECK(p2 == p1);
+
+        // roundtrip
+        CHECK(T(json(p1)) == p1);
+        CHECK(json(T(json(p1))) == json(p1));
+
+        // check exception in case of missing field
+        json j = json(p1);
+        j.erase("age");
+        T p3;
+        CHECK_THROWS_WITH_AS(p3 = json(j), "[json.exception.out_of_range.403] key 'age' not found", json::out_of_range);
+    }
+}