Cross-platform C++ BaseClass and TypeSystem, UnitSystem, Geometry (FreeCAD Base module)

Extracted by Qingfeng Xia, 2019-2021

It is extracted from FreeCAD project, https://github.com/FreeCAD/FreeCAD, it has the same license as FreeCAD: LGPL v2.1+

This piece of code extraction personal work is NOT sponsored by Qingfeng Xia's employment.

v0.19 master branch, Nov 13, 2021.

Features

Most features from FreeCAD Base module, except for XML related IO. Conversion from PyCxx to pybind11 will be experimented here.

• BaseClass and TypeSystem for C++: extracted from FreeCAD's Base module if only TypeSystem is needed, this can be configured by cmake set(FC_TYPESYSTEM_ONLY ON)

• Collection of some header only libraries to catch Python productivity: json, argparse

• Design pattern: Factory, Observer

• Unit and Quantity System

• Fundametnal classes for gometry: Vector3D, Boundbox, Axis, Matrix, Quaternion, VievProjection, 2D Shapes, OpenInventor Builder3D

Todo:

• std::shared_ptr<T> replace all void*
• python wrapping helper, using pybind11

BaseClass

Java and C# base class

C++ does not have a base/root class for all objects, but lot of other high level languages have. see

For a few C++ framework like QT, VTK, GTK, there is base class to provide shared functions see: QT: QObject VTK: vtkObjectBase and vtkObject

Typical functions of base class

1. type system, implemented by c++ macro
2. reference counting, C++11 shared_pointer<> has this function
3. event/observer/subscription pattern, depends on the design of the framework
4. serialization,std::to_string

help on script wrapping

Tutorial for C++ TypeSystem

1. header file In each class's header file (inc. header only class), TYPESYSTEM_HEADER(); must be the first line of that class Just like Q_CLASS for Qt meta system.

class CClass : public Base::BaseClass
{
    TYPESYSTEM_HEADER();

public:
    int d = 0;
};

2. source file In very beginnning of the source file for that class, not within class scope. Or any other cpp file for header only class. TYPESYSTEM_SOURCE(CClass, Base::BaseClass); header only is not supported for static member data declaration.

3. main source file To use this type system: in main() or module initialization function (called in main())

int main()
{
    using namespace Base;

    Type::init(); // init the type system
    // then init each class (actually register this class type), including the BaseClass
    BaseClass::init();  // this root class must be initialized

    // user classes init, can be wrap in a module init()
    CClass::init();



    Type::destruct();
    return 0;
}

see the TypeTest source

Collection of Design pattern

• Design Patterns in C++ with Real Examples https://github.com/ehsangazar/design-patterns-cpp

https://github.com/JakubVojvoda/design-patterns-cpp

included design patterns

• AbstractFactory
• Observor

Collection of some header only libraries

• toml11: header only lib: https://github.com/ToruNiina/toml11

https://github.com/skystrife/cpptoml

• python style C++17 argparse: https://github.com/p-ranav/argparse

• json: https://nlohmann.github.io/json/

see more header-only open source libraries at :https://awesomeopensource.com/projects/header-only

More doc in doc subfolder

<doc/FreeCADBaseChangeLog.md> <doc/PythonBinding.md> <doc/TypeSystem.md>