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 under "Supported datatypes"
22 * Nesting and inheritance is possible
23 * Adapting 3rdparty structs/classes is supported
24 * Basic error handling when deserializing
25 * CMake macro to conveniently include the code generator into the build process
26 * Allow to use Boost.Hana
28 ### Planned features and TODOs
29 There are still things missing which would likely be very useful in practise. The following list contains the
30 open TODOs which are supposed to be most relevant in practise:
32 * [ ] Allow to specify which member variables should be considered
33 * This could work similar to Qt's Signals & Slots macros.
34 * But there should also be a way to do this for 3rdparty types.
35 * Note that currently all public, non-static member variables are (de)serialized.
36 * [ ] Support getter/setter methods
37 * [ ] Allow to serialize the result of methods
38 * [ ] Allow to pass a deserialized value to a method
39 * [ ] Validate enum values when deserializing
40 * [ ] Untie serialization and deserialization
42 For a full list of further ideas, see [TODOs.md](./TODOs.md).
44 ## Supported datatypes
45 The following table shows the mapping of supported C++ types to supported JSON types:
47 | C++ type | JSON type |
48 | ------------------------------------------------------------- |:------------:|
49 | custom structures/classes | object |
50 | `bool` | true/false |
51 | signed and unsigned integral types | number |
52 | `float` and `double` | number |
53 | `enum` and `enum class` | number |
54 | `std::string` | string |
55 | `const char *` | string |
56 | iteratable lists (`std::vector`, `std::list`, ...) | array |
57 | sets (`std::set`, `std::unordered_set`, `std::multiset`, ...) | array |
58 | `std::tuple` | array |
59 | `std::unique_ptr`, `std::shared_ptr` | depends/null |
60 | `std::map`, `std::unordered_map` | object |
61 | `JsonSerializable` | object |
64 * Raw pointer are not supported. This prevents
65 forgetting to free memory which would have to be allocated when deserializing.
66 * For the same reason `const char *` strings are only supported for serialization.
67 * Enums are (de)serialized as their underlying integer value. When deserializing, it is currently *not* checked
68 whether the present integer value is a valid enumeration item.
69 * The JSON type for smart pointer depends on the type the pointer refers to. It can also be `null`.
71 * iteratables must provide an `emplace_back` method. So deserialization of eg. `std::forward_list`
72 is currently not supported.
73 * custom types must provide a default constructor.
74 * constant member variables are skipped.
75 * For custom (de)serialization, see the section below.
78 This example shows how the library can be used to make a `struct` serializable:
80 #include <reflective_rapidjson/json/serializable.h>
82 // define structures, eg.
83 struct TestObject : public ReflectiveRapidJSON::JsonSerializable<TestObject> {
90 struct NestingObject : public ReflectiveRapidJSON::JsonSerializable<NestingObject> {
94 struct NestingArray : public ReflectiveRapidJSON::JsonSerializable<NestingArray> {
96 vector<TestObject> testObjects;
100 NestingArray obj{ ... };
101 cout << "JSON: " << obj.toJson().GetString();
103 // deserialize from JSON
104 const auto obj = NestingArray::fromJson(...);
106 // in exactly one of the project's translation units
107 #include "reflection/code-defining-structs.h"
110 Note that the header included at the bottom must be generated by invoking the code generator appropriately, eg.:
112 reflective_rapidjson_generator \
113 --input-file "$srcdir/code-defining-structs.cpp" \
114 --output-file "$builddir/reflection/code-defining-structs.h"
117 #### Invoking code generator with CMake macro
118 It is possible to use the provided CMake macro to automate the code generator invocation:
120 # find the package and make macro available
121 find_package(reflective-rapidjson REQUIRED)
122 list(APPEND CMAKE_MODULE_PATH ${REFLECTIVE_RAPIDJSON_MODULE_DIRS})
123 include(ReflectionGenerator)
125 # "link" against reflective_rapidjson
126 # it is a header-only lib so this will only add the required include paths
128 target_link_libraries(mytarget PRIVATE reflective_rapidjson)
131 add_reflection_generator_invocation(
132 INPUT_FILES code-defining-structs.cpp
134 OUTPUT_LISTS LIST_OF_GENERATED_HEADERS
135 CLANG_OPTIONS_FROM_TARGETS mytarget
139 This will produce the file `code-defining-structs.h` in the directory `reflection` in the current build directory. So
140 make sure the current build directory is added to the include directories of your target. The default output directory can
141 also be overridden by passing `OUTPUT_DIRECTORY custom/directory` to the arguments.
143 It is possible to specify multiple input files at once. A separate output file is generated for each input. The output files
144 will always have the extension `.h`, independently of the extension of the input file.
146 The full paths of the generated files are also appended to the variable `LIST_OF_GENERATED_HEADERS` which then can be added
147 to the sources of your target. Of course this can be skipped if not required/wanted.
149 The macro will also automatically pass Clang's resource directory which is detected by invoking `clang -print-resource-dir`.
150 To adjust that, just set the cache variable `REFLECTION_GENERATOR_CLANG_RESOURCE_DIR` before including the module.
152 For an explanation of the `CLANG_OPTIONS_FROM_TARGETS` argument, read the next section.
154 #### Passing Clang options
155 It is possible to pass additional options to the Clang tool invocation used by the code generator.
156 This can be done using the `--clang-opt` argument or the `CLANG_OPTIONS` argument when using the CMake macro.
158 For example, additional definitions could be added using `--clang-opt -DSOME_DEFINE -DANOTHER_DEFINE`.
159 But it is actually possible to pass anything from `clang --help`, including the `-X...` options.
161 ##### Specifying Clang's resource directory
162 In case you get a massive number of errors, ensure Clang's resource directory can be located.
163 [Clang documentation](https://clang.llvm.org/docs/LibTooling.html#libtooling-builtin-includes):
165 > The default location to look for builtin headers is in a path `$(dirname /path/to/tool)/../lib/clang/3.3/include` relative to the tool binary.
167 To adjust the default location, just add eg. `--clang-opt -resource-dir /usr/lib/clang/5.0.1` to the arguments.
169 ##### Pass options from regular targets
170 It makes most sense to specify the same options for the code generator as during the actual compilation. This way the code
171 generator uses the same flags, defines and include directories as the compiler and hence behaves like the compiler.
172 When using the CMake macro, it is possible to automatically pass all compile flags, compile definitions and include directories
173 from certain targets to the code generator. Those targets can be specified using the
174 Macro's `CLANG_OPTIONS_FROM_TARGETS` argument.
176 #### Notes regarding cross-compilation
177 * For cross compilation, it is required to build the code generator for the platform you're building on.
178 * Since the code generator is likely not required under the target platform, you should add `-DNO_GENERATOR:BOOL=ON` to the CMake
179 arguments when building Reflective RapidJSON for the target platform.
180 * When using the `add_reflection_generator_invocation` macro, you need to set the following CMake cache variables:
181 * `REFLECTION_GENERATOR_EXECUTABLE:FILEPATH=/path/to/reflective_rapidjson_generator`
182 * specifies the path of the code generator executable built for the platform you're building on
183 * only required if the executable is not in the path anyways
184 * `REFLECTION_GENERATOR_TRIPLE:STRING=machine-vendor-operatingsystem`
185 * specifies the GNU platform triple for the target platform
186 * examples for cross compiling with mingw-w64 under GNU/Linux:
187 `x86_64-w64-mingw32`, `i686-w64-mingw32`
188 * `REFLECTION_GENERATOR_INCLUDE_DIRECTORIES:STRING=/custom/prefix/include`
189 * implicit include directories for target platform
190 * example for cross compiling with mingw-w64 under GNU/Linux:
191 `/usr/lib/gcc/x86_64-w64-mingw32/7.2.1/include;/usr/x86_64-w64-mingw32/include/c++/7.2.1/x86_64-w64-mingw32;/usr/x86_64-w64-mingw32/include`
192 * The Arch Linux packages mentioned at the end of the README file also include `mingw-w64` variants which give a concrete example how
193 cross-compilation can be done.
195 ### Using Boost.Hana instead of the code generator
196 The same example as above. However, this time Boost.Hana is used - so it doesn't require invoking the generator.
199 #include "<reflective_rapidjson/json/serializable-boosthana.h>
201 // define structures using BOOST_HANA_DEFINE_STRUCT, eg.
202 struct TestObject : public JsonSerializable<TestObject> {
203 BOOST_HANA_DEFINE_STRUCT(TestObject,
206 (vector<int>, numbers),
211 struct NestingObject : public JsonSerializable<NestingObject> {
212 BOOST_HANA_DEFINE_STRUCT(NestingObject,
214 (TestObject, testObj)
217 struct NestingArray : public JsonSerializable<NestingArray> {
218 BOOST_HANA_DEFINE_STRUCT(NestingArray,
220 (vector<TestObject>, testObjects)
225 NestingArray obj{ ... };
226 cout << "JSON: " << obj.toJson().GetString();
228 // deserialize from JSON
229 const auto obj = NestingArray::fromJson(...);
232 So beside the `BOOST_HANA_DEFINE_STRUCT` macro, the usage remains the same.
235 * Use of ugly macro required
236 * No context information for errors like type-mismatch available
237 * Inherited members not considered
238 * Proper support for enums is unlikely
240 ### Enable reflection for 3rd party classes/structs
241 It is obvious that the previously shown examples do not work for classes
242 defined in 3rd party header files as it requires adding an additional
245 To work around this issue, one can use the `REFLECTIVE_RAPIDJSON_MAKE_JSON_SERIALIZABLE`
246 macro. It will enable the `toJson` and `fromJson` methods for the specified class
247 in the `ReflectiveRapidJSON::JsonReflector` namespace:
250 // somewhere in included header
251 struct ThridPartyStruct
254 // somewhere in own header or source file
255 REFLECTIVE_RAPIDJSON_MAKE_JSON_SERIALIZABLE(ThridPartyStruct)
258 ReflectiveRapidJSON::JsonReflector::toJson(...).GetString();
259 ReflectiveRapidJSON::JsonReflector::fromJson<ThridPartyStruct>("...");
262 The code generator will emit the code in the same way as if `JsonSerializable` was
265 By the way, the functions in the `ReflectiveRapidJSON::JsonReflector` namespace can also
266 be used when inheriting from `JsonSerializable` (instead of the member functions).
268 ### (De)serializing private members
269 By default, private members are not considered for (de)serialization. However, it is possible
270 to enable this by adding `friend` methods for the helper functions of Reflective RapidJSON.
272 To make things easier, there's a macro provided:
274 struct SomeStruct : public JsonSerializable<SomeStruct> {
275 REFLECTIVE_RAPIDJSON_ENABLE_PRIVATE_MEMBERS(SomeStruct);
278 std::string publicMember = "will be (de)serialized anyways";
281 std::string privateMember = "will be (de)serialized with the help of REFLECTIVE_RAPIDJSON_ENABLE_PRIVATE_MEMBERS macro";
286 * It will obviously not work for 3rd party structs.
287 * This way to allow (de)serialization of private members must be applied when using Boost.Hana
288 and there are any private members present. The reason is that accessing the private members can
289 currently not prevented when using Boost.Hana.
291 ### Custom (de)serialization
292 Sometimes it is appropriate to implement custom (de)serialization. For instance, a
293 custom object representing a time value should likey be serialized as a string rather
294 than an object containing the internal structure.
296 An example for such custom (de)serialization can be found in the file
297 `json/reflector-chronoutilities.h`. It provides (de)serialization of `DateTime` and
298 `TimeSpan` objects from the C++ utilities library mentioned under dependencies.
301 * Static member variables and member functions are currently ignored by the generator.
302 * It is currently not possible to ignore a specific member variable.
305 * Checkout the test cases for further examples. Relevant files are in
306 the directories `lib/tests` and `generator/tests`.
308 [tag editor](https://github.com/Martchus/tageditor), which uses Reflective RapidJSON to provide
310 See [json.h](https://github.com/Martchus/tageditor/blob/master/cli/json.h) and
311 [mainfeatures.cpp#exportToJson](https://github.com/Martchus/tageditor/blob/master/cli/mainfeatures.cpp#L856).
314 The following diagram gives an overview about the architecture of the code generator and wrapper library
317 
319 * blue: classes from LibTooling/Clang
320 * grey: conceivable extension or use
322 ## Install instructions
325 The following dependencies are required at build time. Note that Reflective RapidJSON itself
326 and *none* of these dependencies are required at runtime by an application which makes use of
327 Reflective RapidJSON.
329 * C++ compiler and C++ standard library supporting at least C++14
330 * the [CMake](https://cmake.org) build system
331 * LibTooling from [Clang](https://clang.llvm.org) for the code generator (optional when using
333 * [RapidJSON](https://github.com/Tencent/rapidjson) for JSON (de)serialization
334 * [C++ utilities](https://github.com/Martchus/cpp-utilities) for various helper functions
337 * [Boost.Hana](http://www.boost.org/doc/libs/1_65_1/libs/hana/doc/html/index.html) for using
338 `BOOST_HANA_DEFINE_STRUCT` instead of code generator
339 * [CppUnit](https://www.freedesktop.org/wiki/Software/cppunit) for building and running the tests
340 * [Doxygen](http://www.doxygen.org) for generating API documentation
341 * [Graphviz](http://www.graphviz.org) for diagrams in the API documentation
344 * It is not required to use CMake as build system for your own project. However, when using a
345 different build system, there is no helper for adding the code generator to the build process
347 * I usually develop using the latest version of those dependencies. So it is recommend to get the
348 the latest versions as well. I tested the following versions so far:
349 * GCC 7.2.1/7.3.0 or Clang 5.0 as compiler
350 * libstdc++ from GCC 7.2.1
352 * Clang 5.0.0/5.0.1 for LibTooling
355 * Boost.Hana 1.65.1 and 1.66.0
361 #### 1. Install dependencies
362 Install all required dependencies. Under a typical GNU/Linux system most of these dependencies
363 can be installed via the package manager. Otherwise follow the links in the "Dependencies" section
366 C++ utilities is likely not available as package. However, it is possible to build C++ utilities
367 together with `reflective-rapidjson` to simplify the build process. The following build script makes
368 use of this. (To use system C++ utilities, just skip any lines with "`c++utilities`" in the following
371 #### 2. Make dependencies available
373 When installing (some) of the dependencies at custom locations, it is likely neccassary to tell
374 CMake where to find them. If you installed everything using packages provided by the system,
375 you can skip this step of course.
377 To specify custom locations, just set some environment variables before invoking CMake. This
378 can likely be done in your IDE settings and of course at command line. Here is a Bash example:
380 export PATH=$CUSTOM_INSTALL_PREFIX/bin:$PATH
381 export CMAKE_PREFIX_PATH=$CUSTOM_INSTALL_PREFIX:$CMAKE_PREFIX_PATH
382 export CMAKE_LIBRARY_PATH=$CUSTOM_INSTALL_PREFIX/lib:$CMAKE_LIBRARY_PATH
383 export CMAKE_INCLUDE_PATH=$CUSTOM_INSTALL_PREFIX/include:$CMAKE_INCLUDE_PATH
386 There are also a lot of [useful variables](https://cmake.org/Wiki/CMake_Useful_Variables)
387 that can be specified as CMake arguments. It is also possible to create a
388 [toolchain file](https://cmake.org/cmake/help/v3.10/manual/cmake-toolchains.7.html).
391 #### 3. Get sources, eg. using Git:
394 git clone https://github.com/Martchus/cpp-utilities.git c++utilities
395 git clone https://github.com/Martchus/reflective-rapidjson.git
398 If you don't want to build the development version, just checkout the desired version tag.
400 #### 4. Run the build script
401 Here is an example for building with GNU Make:
406 -DCMAKE_BUILD_TYPE:STRING=Release \
407 -DCMAKE_INSTALL_PREFIX:PATH="/final/install/prefix" \
408 -DBUNDLED_CPP_UTILITIES_PATH:PATH="$SOURCES/c++utilities" \
409 "$SOURCES/reflective-rapidjson"
410 # build library and generators
412 # build and run tests (optional, requires CppUnit)
414 # build tests but do not run them (optional, requires CppUnit)
416 # generate API documentation (optional, reqquires Doxygen)
418 # install header files, libraries and generator
419 make install DESTDIR="/temporary/install/location"
421 Add eg. `-j$(nproc)` to `make` arguments for using all cores.
425 * for PKGBUILDs checkout [my GitHub repository](https://github.com/Martchus/PKGBUILDs) or
426 [the AUR](https://aur.archlinux.org/packages?SeB=m&K=Martchus)
427 * for a binary repository checkout [my website](http://martchus.no-ip.biz/website/page.php?name=programming)
429 * for RPM \*.spec files and binary repository checkout
430 [openSUSE Build Servide](https://build.opensuse.org/project/show/home:mkittler)
432 * for mingw-w64 PKGBUILDs checkout [my GitHub repository](https://github.com/Martchus/PKGBUILDs)
434 These packages shows the required dependencies and commands to build in a plain way. So they might be useful for
435 making Reflective RapidJSON available under other platforms, too.