A true heterogeneous container in modern C++ based on std::any to mimic dynamic property

This property container relies on c++ RTTI. RTTI runtime cost is low for std::any since typeid is fast, but dynamic_cast<> is slow!

See discussion on the cost of RTTI: https://stackoverflow.com/questions/579887/how-expensive-is-rtti

In GCC's preferred ABI, a class vtable always holds a pointer to a per-type RTTI structure, though it might not be used. So a typeid() call itself should only cost as much as any other vtable lookup (the same as calling a virtual member function), and RTTI support shouldn't use any extra space for each object.

For OS without C++17 compiler, boost::any might be used instead. It is possible to mix boost::any and std::any, tested on ubnutu 18.04, libboost 1.65.

This property container is not thread-safe, because STL container std::map is used. By replacing the internal has container with Intel Thread Build Blocks(TBB)'s concurrent hash container type, thread-safe property container might be achieved. It is not yet testec.

json for basic types (as already supported by nlohmann json library) are supported out of box with default json serialization, more user types might be supported by ADL. User serializer and deserializer can be specified when setSerializable(key, value, serializer_function).

Note: this feature is under design, yet fully tested. Also consider save data into the DataStorage class.

• Dynamic Property Maps of boost
• PropertyContainer of FreeCAD: support transaction, serialization, etc
• vtkInformation: https://vtk.org/doc/nightly/html/classvtkInformation.html
• json.hpp: the supported data type are very limited (literal type supported by js)

If an advanced container is needed, such as transaction control, try to use a full-fledged framework like FreeCAD's PropertyContainer

first of all, download Catch2 into this folder,

 - on posix

  g++ -std=c++17 -Wall -I./Catch2/single_include -o PropertyContainerTest PropertyContainerTest.cpp &&
  ./PropertyContainerTest --success

 - on windows
  cl -EHsc -I%CATCH_SINGLE_INCLUDE% PropertyContainerTest.cpp PropertyContainerTest.obj &&
  ./PropertyContainerTest --success

CMakeLists.txt is ready to use, except that Catch2 needs to config/download.