Currently, every single method or constructor which takes an alignment argument
has to be overloaded in order to support the symbolic constants defined by
Gtk::AlignmentEnum.  Just one example:

    void Gtk::Entry::set_alignment(float xalign);
    void Gtk::Entry::set_alignment(AlignmentEnum xalign);

This approach introduces a couple of problems:

a) overloading introduces ambiguities (this particularly problematic with
constructors)
b) overloads make function pointers hard to use
c) there's the risk of forgetting to add an overload
d) methods that take n float arguments would need 2^n overloads in order to
support all possible variants
e) unnecessary bloat (consider link time, symbol resolving on startup, etc.)

I propose to get rid of all these overloads at the next API/ABI break, and to
replace Gtk::AlignmentEnum by float constants:

    namespace Gtk
    {
      const float ALIGN_LEFT   = 0.0;
      const float ALIGN_CENTER = 0.5;
      const float ALIGN_RIGHT  = 1.0;
      const float ALIGN_TOP    = 0.0;
      const float ALIGN_BOTTOM = 1.0;
    }

The only disadvantage would be that the existence of these constants is not
obvious from the method's prototype.  I think this could be solved by adding
some magic to gmmproc to generate appropriate hints in the documentation.