Re: Getting GValue* from Glib::Value

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. 
we switch GDateTime to GObject the situation will be simpler for
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


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
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
 * implementation for custom types will be used. 
"Almost any type" does not include Glib::DateTime, unfortunately.
"All flags and enum types" is not quite right. There are some
types, especailly in glibmm, without a Glib::Value
I think this Glib::Value<Glib::DateTime> specialization will
namespace Glib
template <>
class Value<Glib::DateTime> : public ValueBase_Boxed
  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

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