What is the wrong with my C++ interfacing

[drug]

15.03.2020 22:39, Ferhat Kurtulmuş пишет:
> 
> The original C++ class
> https://github.com/opencv/opencv/blob/master/modules/core/include/opencv2/core/types.hpp#L315: 
> 
> template<typename _Tp> class Size_
> {
> public:
>      typedef _Tp value_type;
> 
>      //! default constructor
>      Size_();
>      Size_(_Tp _width, _Tp _height);
>      Size_(const Size_& sz);
>      Size_(Size_&& sz) CV_NOEXCEPT;
>      Size_(const Point_<_Tp>& pt);
> 
>      Size_& operator = (const Size_& sz);
>      Size_& operator = (Size_&& sz) CV_NOEXCEPT;
>      //! the area (width*height)
>      _Tp area() const;
>      //! aspect ratio (width/height)
>      double aspectRatio() const;
>      //! true if empty
>      bool empty() const;
> 
>      //! conversion of another data type.
>      template<typename _Tp2> operator Size_<_Tp2>() const;
> 
>      _Tp width; //!< the width
>      _Tp height; //!< the height
> };
> 
> // my auxiliary cpp code:
> cv::Size_<int>* createSizeIntWH(int _width, int _height){
>      return new cv::Size_<int>(_width, _height);
> }
> 
> void deleteSizeInt(cv::Size_<int> *&sz){
>      delete sz;
> }
> 
> // d code:
> extern(C++, cv){
> class Size_(_Tp){
>      @disable this();
> 
>      final _Tp area() const;
>      final double aspectRatio() const;
>      final bool empty() const;
> 
>      _Tp width; //!< the width
>      _Tp height; //!< the height
> }
> }
> 
> // my test code that fails:
> Size_!int sz = createSizeIntWH(200, 100);
> writeln(sz.width);

What is the D version of `createSizeIntWH`? In C++ it returns a pointer 
but in D version it returns an instance.

> 
> One of the problems is that sz.width is not printed as 200, but a random 
> int.
> Other problem is that if I try to call one of area, aspectRatio, and 
> empty, it does not compile yielding a linker error:
> error LNK2019: unresolved external symbol "public: int __cdecl 
> cv::Size_<int>::area(void)const " (?area@?$Size_ at H@cv@@QEBAHXZ) 
> referenced in function _Dmain
> Somehow linker cannot locate that symbol. Is this a name mangling issue?
> In the same library I could successfully interface cv::Mat which is a 
> template-free definition. I suspect if D allows interfacing C++ class 
> templates since docs do not cover this, but only struct templates?
>