SwigExtract.h

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#ifndef SWIGEXTRACT_H_
#define SWIGEXTRACT_H_
 
#include <pybind11/pybind11.h>
 
struct PySwigObject {
    PyObject_HEAD
    void * ptr;
    const char * desc;
};
 
 
namespace muq{
namespace Modeling{
 
    class SwigExtract
    {
        
    public:
        SwigExtract(pybind11::object const& objIn) : obj(objIn){};
        
        template<typename T>
        operator T()
        {
            return Cast<T>();
        }
        
        template<typename T>
        T Cast()
        {
            // This functions performs some magic performed by the boost.python folks and described here:
            // https://wiki.python.org/moin/boost.python/HowTo#SWIG_exposed_C.2B-.2B-_object_from_Python
            
            PyObject* objPtr = pybind11::handle(obj).ptr();
            
            char thisStr[] = "this";
            
            //first we need to get the this attribute from the Python Object
            if (!PyObject_HasAttrString(objPtr, thisStr))
                ConversionError<T>();
            
            PyObject* thisAttr = PyObject_GetAttrString(objPtr, thisStr);
            if (thisAttr == NULL)
                ConversionError<T>();   
            
            T* pointer = (T*) ((PySwigObject*)thisAttr)->ptr;
            Py_DECREF(thisAttr);
            
            return *pointer;
        }
        
    private:
        
        pybind11::object const& obj;
        
        template<typename T>
        void ConversionError()
        {   
            throw std::invalid_argument("Unable to convert Python type of " + std::string(pybind11::str(obj.attr("__repr__"))) + " to c++ type of " + std::string(typeid(T).name()));
        }
    };
 
 
} // namepsace Modeling
} // namespace muq
 
#endif