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Merge pull request #2225 from nlohmann/issue2175
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Simplify conversion from/to custom types
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nlohmann authored Jun 29, 2020
2 parents 1b4ea8f + 470f7c0 commit eb7376b
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36 changes: 36 additions & 0 deletions README.md
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Expand Up @@ -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?

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41 changes: 41 additions & 0 deletions include/nlohmann/detail/macro_scope.hpp
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Expand Up @@ -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__)) }
41 changes: 41 additions & 0 deletions single_include/nlohmann/json.hpp
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Expand Up @@ -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
{
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1 change: 1 addition & 0 deletions test/CMakeLists.txt
Original file line number Diff line number Diff line change
Expand Up @@ -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)
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126 changes: 126 additions & 0 deletions test/src/unit-udt_macro.cpp
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@@ -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);
}
}

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