What is the wrong with my C++ interfacing

[Ferhat Kurtulmuş]

On Monday, 16 March 2020 at 07:46:00 UTC, drug wrote:
> On 3/16/20 10:11 AM, Ferhat Kurtulmuş wrote:
>> On Sunday, 15 March 2020 at 22:25:27 UTC, Arine wrote:
>>> On Sunday, 15 March 2020 at 21:27:32 UTC, Ferhat Kurtulmuş
>> 
>>> extern(C++, cv){
>>> extern(C++, class) struct Size_(_Tp){
>>>     @disable this();
>>>     ~this() { }
>>>
>>>     final _Tp area() const;
>>>     final double aspectRatio() const;
>>>     final bool empty() const;
>>>
>>>     _Tp width; //!< the width
>>>     _Tp height; //!< the height
>>> }
>>> }
>>>
>>> extern(C++){
>>>     cv.Size_!int* createSizeIntWH(int w, int h);
>>> }
>>>
>>> void main()
>>> {
>>>     Size_!int* sz = createSizeIntWH(200, 100);
>>>     writeln(sz.width);
>>> }
>> 
>> This worked for me too. But member functions are still causing 
>> linker error. It seems like docs 
>> (https://dlang.org/spec/cpp_interface.html) do not cover those 
>> situations. Is there any other sources to read for it. Maybe 
>> you make a pull request to docs covering C++ interfacing tips 
>> in detail.
>
> Not tested:
>
>  extern(C++, class) struct Size_(_Tp){
>      @disable this();
>      ~this() { }
> extern(C++): // <- IIRC linkage should be set for members 
> separately from aggregate
>      final _Tp area() const;
>      final double aspectRatio() const;
>      final bool empty() const;
>
>      _Tp width; //!< the width
>      _Tp height; //!< the height
>  }

Ok, here is a solution. I opened my lib (yielded by my auxilary 
cpp) using 7zip. There are two files containing symbol names, 
1.txt and 2.txt. I searched for names of member functions. They 
were not there because c++ compiler does not compile member 
functions of class templates because we don't actually use them. 
So, I simply include this line in my aux cpp file and recompiled 
it:

template class cv::Size_<int>;

I reopened 1.txt and they are there now:

?area@?$Size_ at H@cv@@QEBAHXZ
?aspectRatio@?$Size_ at H@cv@@QEBANXZ

now everything works :D