3 The main goal of this project is to provide a code generator for serializing/deserializing C++ objects to/from JSON
4 using Clang and RapidJSON.
6 However, extending the generator to generate code for other applications of reflection or to provide generic
7 reflection would be possible as well.
9 ## Open for other reflection approaches
10 The reflection implementation used behind the scenes of this library is exchangeable:
12 * This repository already provides a small, additional header to use RapidJSON with Boost.Hana. This allows to
13 serialize or dezerialize simple data structures declared using the `BOOST_HANA_DEFINE_STRUCT` macro rather than
14 requiring the code generator.
15 * When native reflection becomes standardized, it would be possible to make use of it as well. In this case,
16 the code generator could still act as a fallback.
19 The basic functionality is implemented, tested and documented:
21 * serialization and deserialization of datatypes listed above
22 * nesting and inheritance is possible
23 * basic error handling when deserializing
24 * CMake macro to conveniently include the code generator into the build process
25 * allow to use Boost.Hana
28 There are still things missing which would likely be very useful in practise. The following list contains
29 the most important TODOs:
31 * [ ] Allow to specify which member variables should be considered.
32 * This could work similar to Qt's Signals & Slots
33 * but there should also be a way to do this for 3rdparty types.
34 * Note that currently, *all* public member variables are (de)serialized.
35 * [ ] Support getter/setter methods
36 * [ ] Allow to serialize the result of methods.
37 * [ ] Allow to pass a deserialized value to a method.
38 * [ ] Validate enum values when deserializing.
39 * [ ] Untie serialization and deserialization.
41 ## Supported datatypes
42 The following table shows the mapping of supported C++ types to supported JSON types:
44 | C++ type | JSON type |
45 | ------------------------------------------------- |:------------:|
46 | custom structures/classes | object |
47 | `bool` | true/false |
48 | signed and unsigned integral types | number |
49 | `float` and `double` | number |
50 | `enum` and `enum class` | number |
51 | `std::string` | string |
52 | `const char *` | string |
53 | iteratable lists (`std::vector`, `std::list`, ...)| array |
54 | `std::tuple` | array |
55 | `std::unique_ptr`, `std::shared_ptr` | depends/null |
56 | `std::map`, `std::unordered_map` | object |
57 | `JsonSerializable` | object |
60 * Raw pointer are not supported. This prevents
61 forgetting to free memoery which would have to be allocated when deserializing.
62 * For the same reason `const char *` strings are only supported for serialization.
63 * Enums are (de)serialized as their underlying integer value. When deserializing, it is currently *not* checked
64 whether the present integer value is a valid enumeration item.
65 * The JSON type for smart pointer depends on the type the pointer refers to. It can also be `null`.
67 * iteratables must provide an `emplace_back` method. So deserialization of eg. `std::forward_list`
68 is currently not supported.
69 * custom types must provide a default constructor.
70 * constant member variables are skipped.
71 * For custom (de)serialization, see the section below.
74 This example shows how the library can be used to make a `struct` serializable:
76 #include <reflective-rapidjson/json/serializable.h>
78 // define structures, eg.
79 struct TestObject : public JsonSerializable<TestObject> {
86 struct NestingObject : public JsonSerializable<NestingObject> {
90 struct NestingArray : public JsonSerializable<NestingArray> {
92 vector<TestObject> testObjects;
96 NestingArray obj{ ... };
97 cout << "JSON: " << obj.toJson().GetString();
99 // deserialize from JSON
100 const auto obj = NestingArray::fromJson(...);
102 // in exactly one of the project's translation units
103 #include "reflection/code-defining-structs.h"
106 Note that the header included at the bottom must be generated by invoking the code generator appropriately, eg.:
108 reflective_rapidjson_generator -i "$srcdir/code-defining-structs.cpp" -o "$builddir/reflection/code-defining-structs.h"
111 #### Invoking code generator with CMake macro
112 It is possible to use the provided CMake macro to automate this task:
114 # find the package and make macro available
115 find_package(reflective-rapidjson REQUIRED)
116 list(APPEND CMAKE_MODULE_PATH ${REFLECTIVE_RAPIDJSON_MODULE_DIRS})
117 include(ReflectionGenerator)
119 # "link" against reflective_rapidjson (it is a header-only lib so this will only add the required include paths to your target)
120 target_link_libraries(mytarget PRIVATE reflective_rapidjson)
123 add_reflection_generator_invocation(
124 INPUT_FILES code-defining-structs.cpp
126 OUTPUT_LISTS LIST_OF_GENERATED_HEADERS
127 CLANG_OPTIONS_FROM_TARGETS mytarget
131 This will produce the file `code-defining-structs.h` in the directory `reflection` in the current build directory. So
132 make sure the current build directory is added to the include directories of your target. The default output directory can
133 also be overridden by passing `OUTPUT_DIRECTORY custom/directory` to the arguments.
135 It is possible to specify multiple input files at once. A separate output file is generated for each input. The output files
136 will always have the extension "`.h`", independently of the extension of the input file.
138 The full paths of the generated files are also appended to the variable `LIST_OF_GENERATED_HEADERS` which then can be added
139 to the sources of your target. Of course this can be skipped if not required/wanted.
141 For an explanation of the `CLANG_OPTIONS_FROM_TARGETS` argument, read the next section.
143 #### Passing Clang options
144 It is possible to pass additional options to the Clang tool invocation used by the code generator.
145 This can be done using the `--clang-opt` argument or the `CLANG_OPTIONS` argument when using the CMake macro.
147 It makes most sense to specify the same options for the code generator as during the actual compilation. This way the code
148 generator uses the same flags, defines and include directories as the compiler and hence behaves like the compiler.
149 When using the CMake macro, it is possible to automatically pass all compile flags, compile definitions and include directories
150 from certain targets to the code generator. The targets can be specified using the `CLANG_OPTIONS_FROM_TARGETS` argument.
152 #### Notes regarding cross-compilation
153 * For cross compilation, it is required to build the code generator for the platform you're building on.
154 * Since the code generator is likely not required under the target platform, you should add `-DNO_GENERATOR:BOOL=ON` to the CMake
155 arguments when building Reflective RapidJSON for the target platform.
156 * When using the `add_reflection_generator_invocation` macro, you need to set the following CMake variables:
157 * `REFLECTION_GENERATOR_EXECUTABLE:FILEPATH=/path/to/executable`: path of the code generator executable to run under the platform
159 * `REFLECTION_GENERATOR_INCLUDE_DIRECTORIES:STRING=/custom/prefix/include`: directories containing header files for target
160 platform (not required if you set `CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES` anyways since it defaults to that variable)
161 * It is likely required to pass additional options for the target platform. For example, to cross compile with MingGW, is is
162 required to add `-fdeclspec`, `-D_WIN32` and some more options (see `lib/cmake/modules/ReflectionGenerator.cmake`). The
163 `add_reflection_generator_invocation` macro is supposed to take care of this, but currently only MingGW is supported.
164 * The Arch Linux packages mentioned at the end of the README file also include `mingw-w64` variants which give a concrete example how
165 cross-compilation can be done.
167 ### Using Boost.Hana instead of the code generator
168 The same example as above. However, this time Boost.Hana is used - so it doesn't require invoking the generator.
171 #include "<reflective-rapidjson/json/serializable-boosthana.h>
173 // define structures using BOOST_HANA_DEFINE_STRUCT, eg.
174 struct TestObject : public JsonSerializable<TestObject> {
175 BOOST_HANA_DEFINE_STRUCT(TestObject,
178 (vector<int>, numbers),
183 struct NestingObject : public JsonSerializable<NestingObject> {
184 BOOST_HANA_DEFINE_STRUCT(NestingObject,
186 (TestObject, testObj)
189 struct NestingArray : public JsonSerializable<NestingArray> {
190 BOOST_HANA_DEFINE_STRUCT(NestingArray,
192 (vector<TestObject>, testObjects)
197 NestingArray obj{ ... };
198 cout << "JSON: " << obj.toJson().GetString();
200 // deserialize from JSON
201 const auto obj = NestingArray::fromJson(...);
204 So beside the `BOOST_HANA_DEFINE_STRUCT` macro, the usage remains the same.
207 * Use of ugly macro required
208 * No context information for errors like type-mismatch available
209 * Inherited members not considered
210 * Support for enums is unlikely
211 * Attempt to access private members can not be prevented
213 ### Enable reflection for 3rd party classes/structs
214 It is obvious that the previously shown examples do not work for classes
215 defined in 3rd party header files as it requires adding an additional
218 To work around this issue, one can use the `REFLECTIVE_RAPIDJSON_MAKE_JSON_SERIALIZABLE`
219 macro. It will enable the `toJson` and `fromJson` methods for the specified class
220 in the `ReflectiveRapidJSON::JsonReflector` namespace:
223 // somewhere in included header
224 struct ThridPartyStruct
227 // somewhere in own header or source file
228 REFLECTIVE_RAPIDJSON_MAKE_JSON_SERIALIZABLE(ThridPartyStruct)
231 ReflectiveRapidJSON::JsonReflector::toJson(...).GetString();
232 ReflectiveRapidJSON::JsonReflector::fromJson<ThridPartyStruct>("...");
235 The code generator will emit the code in the same way as if `JsonSerializable` was
238 By the way, the functions in the `ReflectiveRapidJSON::JsonReflector` namespace can also
239 be used when inheriting from `JsonSerializable` (instead of the member functions).
241 ### (De)serializing private members
242 By default, private members are not considered for (de)serialization. However, it is possible
243 to enable this by adding `friend` methods for the helper functions of Reflective RapidJSON.
245 To make things easier, there's a macro provided:
247 struct SomeStruct : public JsonSerializable<SomeStruct> {
248 REFLECTIVE_RAPIDJSON_ENABLE_PRIVATE_MEMBERS(SomeStruct);
251 std::string publicMember = "will be (de)serialized anyways";
254 std::string privateMember = "will be (de)serialized with the help of REFLECTIVE_RAPIDJSON_ENABLE_PRIVATE_MEMBERS macro";
259 * It will obviously not work for 3rd party structs.
260 * This way to allow (de)serialization of private members must be applied when using Boost.Hana
261 and there are any private members present. The reason is that accessing the private members can
262 currently not prevented when using Boost.Hana.
264 ### Custom (de)serialization
265 Sometimes it is appropriate to implement custom (de)serialization. For instance, a
266 custom object representing a time value should likey be serialized as a string rather
267 than an object with the internal data members.
269 An example for such custom (de)serialization can be found in the file
270 `json/reflector-chronoutilities.h`. It provides (de)serialization of `DateTime` and
271 `TimeSpan` objects from the C++ utilities library.
274 * Static member variables are currently ignored by the generator.
275 * It is currently not possible to ignore a specific member.
278 * Checkout the test cases for further examples. Relevant files are in
279 the directories `lib/tests` and `generator/tests`.
281 [tag editor](https://github.com/Martchus/tageditor), which uses Reflective RapidJSON to provide
283 See [json.h](https://github.com/Martchus/tageditor/blob/master/cli/json.h) and
284 [mainfeatures.cpp#exportToJson](https://github.com/Martchus/tageditor/blob/master/cli/mainfeatures.cpp#L856).
287 The following diagram gives an overview about the architecture of the code generator and wrapper library
290 
292 * blue: classes from LibTooling/Clang
293 * grey: conceivable extension or use
295 ## Install instructions
298 The following dependencies are required at build time. Note that Reflective RapidJSON itself
299 and *none* of these dependencies are required at runtime by an application which makes use of
300 Reflective RapidJSON.
302 * C++ compiler and C++ standard library supporting at least C++14
303 * the [CMake](https://cmake.org) build system
304 * LibTooling from [Clang](https://clang.llvm.org) for the code generator (optional when using
306 * [RapidJSON](https://github.com/Tencent/rapidjson) for JSON (de)serialization
307 * [C++ utilities](https://github.com/Martchus/cpp-utilities) for various helper functions
310 * [Boost.Hana](http://www.boost.org/doc/libs/1_65_1/libs/hana/doc/html/index.html) for using
311 `BOOST_HANA_DEFINE_STRUCT` instead of code generator
312 * [CppUnit](https://www.freedesktop.org/wiki/Software/cppunit) for building and running the tests
313 * [Doxygen](http://www.doxygen.org) for generating API documentation
314 * [Graphviz](http://www.graphviz.org) for diagrams in the API documentation
317 * It is not required to use CMake as build system for your own project. However, when using a
318 different build system, there is no helper for adding the code generator to the build process
320 * I usually develop using the latest version of those dependencies. So it is recommend to get the
321 the latest versions as well. I tested the following versions so far:
322 * GCC 7.2.1 or Clang 5.0 as compiler
323 * libstdc++ from GCC 7.2.1
325 * Clang 5.0.0/5.0.1 for LibTooling
328 * Boost.Hana 1.65.1 and 1.66.0
334 #### 1. Install dependencies
335 Install all required dependencies. Under a typical GNU/Linux system most of these dependencies
336 can be installed via the package manager. Otherwise follow the links in the "Dependencies" section
339 C++ utilities is likely not available as package. However, it is possible to build C++ utilities
340 together with `reflective-rapidjson` to simplify the build process. The following build script makes
341 use of this. (To use system C++ utilities, just skip any lines with "`c++utilities`" in the following
344 #### 2. Make dependencies available
346 When installing (some) of the dependencies at custom locations, it is likely neccassary to tell
347 CMake where to find them. If you installed everything using packages provided by the system,
348 you can skip this step of course.
350 To specify custom locations, just set some environment variables before invoking CMake. This
351 can likely be done in your IDE settings and of course at command line. Here is a Bash example:
353 export PATH=$CUSTOM_INSTALL_PREFIX/bin:$PATH
354 export CMAKE_PREFIX_PATH=$CUSTOM_INSTALL_PREFIX:$CMAKE_PREFIX_PATH
355 export CMAKE_LIBRARY_PATH=$CUSTOM_INSTALL_PREFIX/lib:$CMAKE_LIBRARY_PATH
356 export CMAKE_INCLUDE_PATH=$CUSTOM_INSTALL_PREFIX/include:$CMAKE_INCLUDE_PATH
359 There are also a lot of [useful variables](https://cmake.org/Wiki/CMake_Useful_Variables)
360 that can be specified as CMake arguments. It is also possible to create a
361 [toolchain file](https://cmake.org/cmake/help/v3.10/manual/cmake-toolchains.7.html).
364 #### 3. Get sources, eg. using Git:
367 git clone https://github.com/Martchus/cpp-utilities.git c++utilities
368 git clone https://github.com/Martchus/reflective-rapidjson.git
371 If you don't want to build the development version, just checkout the desired version tag.
373 #### 4. Run the build script
374 Here is an example for building with GNU Make:
379 -DCMAKE_BUILD_TYPE:STRING=Release \
380 -DCMAKE_INSTALL_PREFIX:PATH="/final/install/prefix" \
381 -DBUNDLED_CPP_UTILITIES_PATH:PATH="$SOURCES/c++utilities" \
382 "$SOURCES/reflective-rapidjson"
383 # build library and generators
385 # build and run tests (optional, requires CppUnit)
387 # build tests but do not run them (optional, requires CppUnit)
389 # generate API documentation (optional, reqquires Doxygen)
391 # install header files, libraries and generator
392 make install DESTDIR="/temporary/install/location"
394 Add eg. `-j$(nproc)` to `make` arguments for using all cores.
397 I currently only provide an
398 [Arch Linux package](https://github.com/Martchus/PKGBUILDs/blob/master/reflective-rapidjson/git/PKGBUILD)
399 for the current Git version. This package shows the required dependencies and commands to build
400 in a plain way. So it might be useful for making Reflective RapidJSON available under other platforms,