Re: How to use Glib::Value?

[Kjell Ahlstedt <kjellahlstedt gmail com>]

init() is a method in Glib::ValueBase, base class of all Glib::Value<> specializations. The documentation says
    init() is not implemented as constructor, to avoid the necessity
    to implement a forward constructor in each derived class.
There are many subclasses of Glib::ValueBase. Most of these subclasses (perhaps even all of them) has just compiler-generated constructors. I suppose someone found it tedious to write constructors with a call to init() in all those subclasses. It's not obvious to me that it was a wise decision not to do that.

On 2019-03-05 14:37, Pavlo Solntsev via gtkmm-list wrote:

Thanks, that works. Out of curiosity, why not to call init() in the
constructor? 


On Tue, 2019-03-05 at 11:00 +0100, Kjell Ahlstedt wrote:

Replace
   data.init(G_TYPE_DATE_TIME);
by
   data.init(data.value_type());
or
   data.init(Glib::Value<Glib::DateTime>::value_type());
You don't store a GDateTime, you store a Glib::DateTime. That's not
the same thing.
This is not well described in the documentation, but there is an
example at
https://gitlab.gnome.org/GNOME/glibmm/blob/master/tests/glibmm_value/main.cc
On 2019-03-04 14:05, Pavlo Solntsev via gtkmm-list wrote:

Hi,

Have this code 
```
Glib::Value<int> datai;
datai.init(G_TYPE_INT);
datai.set(8);
std::cout << "Value = " << datai.get() << std::endl;
```
I see in stdout:
Value = 8

Works good. Now I would like to use another type: Glib::DateTime
```
Glib::Value<Glib::DateTime> data;

data.init(G_TYPE_DATE_TIME);
Glib::DateTime ctime = Glib::DateTime::create_now_utc();
data.set(ctime);
```

This compiles ok, but generates 
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7b2405c in Glib::DateTime::operator= (this=0x0, src=""
at

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/home/pavlo/jhbuild/checkout/glibmm-2.4/glib/glibmm/datetime.cc:89
89	  if(gobject_)