Re: Getting GValue* from Glib::Value

[p sun fun gmail com]

Glib maintainer also wants no change in the implementation of
GDateTime. I like your strategy. Thanks.


On Thu, 2019-04-25 at 13:55 +0200, Kjell Ahlstedt wrote:
> Don't change GDateTime in glib because of Glib::Value<>.
> Many boxed types get Glib::Value specializations almost
> automatically. Those that are wrapped as _CLASS_OPAQUE_COPYABLE
> don't. GDateTime is one of them. I'll either add the Glib::Value
> specialization manually to glibmm/datetime.h or make a more general
> fix in the _CLASS_OPAQUE_COPYABLE m4 macro.
> For the time being I can fix something in the master branch. A fix in
> the glibmm-2.4 ABI series has to wait until glibmm 2.62.0. However I
> fix it, the fix will include added API and/or ABI.
> On 2019-04-24 18:06, Pavlo Solntsev via gtkmm-list wrote:
> > Thank you Kjell.
> >
> > It works. Basically, the code you provided should be added to the
> > header (glibmm/value.h). Currently, GDateTime is not GObject-based. 
> > If
> > we switch GDateTime to GObject the situation will be simpler for
> > mm.
> > For my problem, I will use code in my app. Does it make sense to
> > add it
> > to the master (glibmm)? Or it is better change GDateTime
> > implementation. 
> >
> > Thanks.
> >
> >
> > On Wed, 2019-04-24 at 14:45 +0200, Kjell Ahlstedt wrote:
> > > The description of Glib::ValueBase says
> > >  * Glib::Value<> is specialized for almost any type used within
> > > the
> > > glibmm and gtkmm libraries.
> > >  *
> > >  * - Basic types like <tt>int</tt>, <tt>char</tt>, <tt>bool</tt>,
> > > etc., also <tt>void*</tt>.
> > >  * - Glib::ustring and std::string.
> > >  * - Pointers to classes derived from Glib::Object.
> > >  * - Glib::RefPtr<> pointer types, which are assumed to be
> > > Glib::Object pointers.
> > >  * - All flags and enum types used within the gtkmm libraries.
> > >  *
> > >  * If a type doesn't fit into any of these categories, then a
> > > generic
> > >  * implementation for custom types will be used. 
> > > "Almost any type" does not include Glib::DateTime, unfortunately.
> > > And
> > > "All flags and enum types" is not quite right. There are some
> > > enum
> > > types, especailly in glibmm, without a Glib::Value
> > > specialization.
> > > I think this Glib::Value<Glib::DateTime> specialization will
> > > work:
> > > namespace Glib
> > > {
> > > template <>
> > > class Value<Glib::DateTime> : public ValueBase_Boxed
> > > {
> > > public:
> > >   using CppType = Glib::DateTime;
> > >   using CType = GDateTime*;
> > >
> > >   static GType value_type() { return G_TYPE_DATE_TIME; }
> > >
> > >   void set(const CppType& data) { set_boxed(data.gobj()); }
> > >   CppType get() const { return
> > > CppType(static_cast<CType>(get_boxed()), true); }
> > > };
> > > } // namespace Glib