Re: Getting GValue* from Glib::Value

[p sun fun gmail com]

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
>
> On 2019-04-23 15:01, p sun fun gmail com wrote:
> > Thanks, Kjell. I missed that gobj() returns a pointer to gobject_.
> > However, the returned type is not a pure C gtype. Let me illustrate
> > this by example:
> >
> > ```
> >   Glib::Value<Glib::DateTime> data;
> >
> >   data.init(data.value_type());
> >
> >   const GValue *val = data.gobj();
> >   std::cout << "val type is " << G_VALUE_TYPE_NAME(val) <<
> > std::endl;
> >
> >   GValue *val2 = g_new0(GValue, 1);
> >   g_value_init(val2, G_TYPE_DATE_TIME);
> >   std::cout << "val2 type is " << G_VALUE_TYPE_NAME(val2) <<
> > std::endl;
> >
> > ```
> > In stdout I see
> >
> > ```
> > val type is glibmm__CustomBoxed_N4Glib8DateTimeE
> > val2 type is GDateTime
> > ```
> >
> > I know that GDateTime is a boxed type and Glib::Value registers it
> > own
> > type. If I use built-in type, e.g. int, I see the same type for C++
> > and
> > C parts. Basically, my question should be refined and tailed to the
> > conversion of C++ gtype (boxed equivalent) to the C-like gtype. 
> >
> > Thanks.