Created attachment 80087 [details] [review]
patch that attempts to fix this

I was wondering how come that this is the only file being reported, but actualy this is the only place (in .ccg files) where unwrap is called for a const RefPtr<const T>. Such RefPtr and an unwrap() appear in style.ccg, in set_bg_pixmap(), starting at line 173, but it is first cast_const() to a RefPtr<T> and then that new pointer is passed to unwrap_copy(). Which is a different case.

So my guess is that if these unwrap() calls are first called to return to an explicit const GtkSomeType*, then these errors would not be reported.

I eventually figured out how to regenerate the gtk/gtkmm/printoperations.cc from the source file, and the error has now moved:

 CC -DHAVE_CONFIG_H -DG_LOG_DOMAIN=\"gtkmm\" -I../../gtk -I../../gtk -I../../pango -I../../pango -I../../atk -I../../atk -I../../gdk -I../../gdk -I../../gtk -I../../gtk -I/local/gnu/include/glibmm-2.4 -I/local/gnu/lib/64/glibmm-2.4/include -I/local/gnu/include/sigc++-2.0 -I/local/gnu/lib/64/sigc++-2.0/include -I/local/gnu/include/glib-2.0 -I/local/gnu/lib/64/glib-2.0/include -I/local/include/cairomm-1.0 -I/local/include/cairo -I/local/gnu/include/gtk-2.0 -I/local/gnu/lib/64/gtk-2.0/include -I/local/gnu/include/atk-1.0 -I/local/gnu/include/pango-1.0 -I/local/gnu/include/gtk-unix-print-2.0 -mt -I/local/gnu/include/glib-2.0 -I/local/gnu/lib/64/glib-2.0/include -I/local/gnu/include -I/local/include -xO3 -KPIC -xtarget=native -xarch=amd64 -I/local/gnu/include -I/local/include -c printoperation.cc  -KPIC -DPIC -o .libs/printoperation.o
"printoperation.cc", line 87: Error: Overloading ambiguity between "Glib::unwrap<Gtk::PageSetup>(const Glib::RefPtr<const Gtk::PageSetup>&)" and "Glib::unwrap<const Gtk::PageSetup>(const Glib::RefPtr<const Gtk::PageSetup>&)".
"printoperation.cc", line 88: Error: Overloading ambiguity between "Glib::unwrap<Gtk::PrintSettings>(const Glib::RefPtr<const Gtk::PrintSettings>&)" and "Glib::unwrap<const Gtk::PrintSettings>(const Glib::RefPtr<const Gtk::PrintSettings>&)".
"printoperation.cc", line 105: Error: Overloading ambiguity between "Glib::unwrap<Gtk::PageSetup>(const Glib::RefPtr<const Gtk::PageSetup>&)" and "Glib::unwrap<const Gtk::PageSetup>(const Glib::RefPtr<const Gtk::PageSetup>&)".
"printoperation.cc", line 106: Error: Overloading ambiguity between "Glib::unwrap<Gtk::PrintSettings>(const Glib::RefPtr<const Gtk::PrintSettings>&)" and "Glib::unwrap<const Gtk::PrintSettings>(const Glib::RefPtr<const Gtk::PrintSettings>&)".


Lines 87 & 88 are:

  const GtkPageSetup* c_page_setup = Glib::unwrap(page_setup);
  const GtkPrintSettings* c_print_settings = Glib::unwrap(print_settings);

Could you please try specifying a template specialization, to avoid the error like so:

Glib::unwrap<const GtkPageSetup*>(page_setup)

If you make a new patch, please add comments next to the code explaining why that has been done, so it will not be removed by someone in the future.

Created attachment 80113 [details] [review]
patch 2, with template specialization

Tim, can you try with this patch?

Don't know how that happenned, I just typed 'patch 2' and it became a link to something. Please ignore that one.

Thanks for making the patch Marko.

Unfortunately, still no joy:

"printoperation.cc", line 91: Error: Overloading ambiguity between "Glib::unwrap<const Gtk::PageSetup>(const Glib::RefPtr<const Gtk::PageSetup>&)" and "Glib::unwrap<const Gtk::PageSetup>(const Glib::RefPtr<const Gtk::PageSetup>&)".
"printoperation.cc", line 94: Error: Overloading ambiguity between "Glib::unwrap<const Gtk::PrintSettings>(const Glib::RefPtr<const Gtk::PrintSettings>&)" and "Glib::unwrap<const Gtk::PrintSettings>(const Glib::RefPtr<const Gtk::PrintSettings>&)".
"printoperation.cc", line 115: Error: Overloading ambiguity between "Glib::unwrap<const Gtk::PageSetup>(const Glib::RefPtr<const Gtk::PageSetup>&)" and "Glib::unwrap<const Gtk::PageSetup>(const Glib::RefPtr<const Gtk::PageSetup>&)".
"printoperation.cc", line 118: Error: Overloading ambiguity between "Glib::unwrap<const Gtk::PrintSettings>(const Glib::RefPtr<const Gtk::PrintSettings>&)" and "Glib::unwrap<const Gtk::PrintSettings>(const Glib::RefPtr<const Gtk::PrintSettings>&)".


I have regenerated printoperation.cc, and it includes Marko's second patch.
Line 91 is the last line I show:


  // Specify the exact type with template specialization, to avoid possible
  // ambiguities between the const and non-const versions of unwrap reported
  // by some compilers:
  const GtkPageSetup* c_page_setup =
    Glib::unwrap<const PageSetup>(page_setup);

Created attachment 80136 [details] [review]
third attempt

Ok, try with this one. I kinda don't like it, but maybe it'll solve the problem. Here, the idea is to do eg:

Glib::RefPtr<PageSetup> page_setup_unconst =
    Glib::RefPtr<PageSetup>::cast_const(page_setup);

and then use that new one with unwrap().

> "printoperation.cc", line 91: Error: Overloading ambiguity between
> "Glib::unwrap<const Gtk::PageSetup>(const Glib::RefPtr<const Gtk::PageSetup>&)"
> and
> "Glib::unwrap<const Gtk::PageSetup>(const Glib::RefPtr<const Gtk::PageSetup>&)".

Well this makes no sense to me. They are the same, though I guess it thinks it is referring to these two partial template specializations from glibmm's wrap.h:

template <class T> inline
const typename T::BaseObjectType* unwrap(const T* ptr)
{
  return (ptr) ? ptr->gobj() : 0;
}

template <class T> inline
typename T::BaseObjectType* unwrap(const Glib::RefPtr<T>& ptr)
{
  return (ptr) ? ptr->gobj() : 0;
}

We already use this specifying-the-specialization trick elsewhere in gtkmm, using the __CONVERT_CONST_REFPTR_TO_P_SUN() macro in our .m4 conversion files, but I wonder why it isn't work for this example:

# The Sun Forte compiler doesn't seem to be able to handle these, so we are using the altlernative,  __CONVERT_CONST_REFPTR_TO_P_SUN.
# The Sun compiler gives this error, for instance:
#  "widget.cc", line 4463: Error: Overloading ambiguity between "Glib::unwrap<Gdk::Window>(const Glib::RefPtr<const Gdk::Window>&)" and
# "Glib::unwrap<const Gdk::Window>(const Glib::RefPtr<const Gdk::Window>&)".
#
define(`__CONVERT_CONST_REFPTR_TO_P_SUN',`const_cast<$`'2>(Glib::unwrap<$1>($`'3))')

You might even be able to use that macro in the .ccg file.

Marko's patch #3 worked.  The compile is now proceeding onward.  Thanks much to both of you for your efforts!

Created attachment 80154 [details] [review]
another take on template specialization

Glad to hear :).

Can you also try with this one, please? It's similar to the second one, only simpler. I just added the specialization to <GtkmmType> to the original code, instead of having a separate call with a specialization to <const GtkmmType>.

Sorry for the delay.  I tested patch #4, and it also works just fine.

Looks good, though I'm surprised that it works.

Changes as in #4 committed.

Many thanks, Marko.