Re: Linking Ada to C++ Overloaded Functions and Methods

[Ron Wills <ron.rwsoft@gmail.com>]

On Saturday, April 7, 2018 at 1:05:24 PM UTC-6, Niklas Holsti wrote:
> On 18-04-07 21:35 , Ron Wills wrote:
> > I know that both Ada and C++ can overload functions and methods. The problem I'm having is when I'm trying to link Ada to overload C++ functions. I know I could use different Ada names, but if it's possible to keep the same names in Ada it would save a lot of re-coding.
> >
> > An example is from the FLTK library. The "draw_box" method from the Fl_Widget class is overloaded and I get the following from g++ -fdump-ada-spec.
> >
> > procedure draw_box (this : access constant Fl_Widget'Class);
> > pragma Import (CPP, draw_box, "_ZNK9Fl_Widget8draw_boxEv");
> >
> > procedure draw_box
> >   (this : access constant Fl_Widget'Class;
> >    t : Fl_Enumerations_H.Fl_Boxtype;
> >    c : Fl_Enumerations_H.Fl_Color);  -- /usr/include/Fl/Fl_Widget.H:181
> > pragma Import (CPP, draw_box, "_ZNK9Fl_Widget8draw_boxE10Fl_Boxtypej");
> >
> > The C++ name mangling works to uniquely identify the C++ methods, but the compiler is choking on the Ada names as already being declared.
> >
> > fl_fl_widget_h.ads:171:07: entity "draw_box" was previously imported
> > fl_fl_widget_h.ads:171:07: (pragma "Import" applies to all previous entities)
> > fl_fl_widget_h.ads:171:07: import not allowed for "draw_box" declared at line 164
> > fl_fl_widget_h.ads:181:07: entity "draw_box" was previously imported
> > fl_fl_widget_h.ads:181:07: (pragma "Import" applies to all previous entities)
> > fl_fl_widget_h.ads:181:07: import not allowed for "draw_box" declared at line 167
> >
> > Is there a way to use overloaded Ada names with C++ or do I need to find a unique Ada name for every C++ overload method?
> >
> 
> I would try to change the pragma Imports into aspects, something like this:
> 
> procedure draw_box (....)
> with Import,
>       Convention => CPP,
>       Link_Name => "_ZNK9Fl_Widget8draw_boxE10Fl_Boxtypej";

That worked perfectly! Thanks!

> Aspects are syntactically tied to the subprogram declaration in which 
> they occur, so overloaded subprograms with the same identifier can be 
> given different aspect values, unlike for pragma Import.
> 
> Note that I'm not fully sure if you should use the Link_Name aspect or 
> the External_Name aspect. The C++ identifiers given in the pragma 
> Imports are External_Name values, but I think they are also Link_Name 
> values.
> 
> -- 
> Niklas Holsti
> Tidorum Ltd
> niklas holsti tidorum fi
>        .      @       .