1 <?xml version='1.0' encoding="ISO-8859-1"?>
3 <chapter id="chapter-gobject">
4 <title>The GObject base class</title>
7 The two previous chapters discussed the details of Glib's Dynamic Type System
8 and its signal control system. The GObject library also contains an implementation
9 for a base fundamental type named <type><link linkend="GObject">GObject</link></type>.
13 <type><link linkend="GObject">GObject</link></type> is a fundamental classed instantiable type. It implements:
15 <listitem><para>Memory management with reference counting</para></listitem>
16 <listitem><para>Construction/Destruction of instances</para></listitem>
17 <listitem><para>Generic per-object properties with set/get function pairs</para></listitem>
18 <listitem><para>Easy use of signals</para></listitem>
20 All the GTK+ objects and all of the objects in Gnome libraries which use the GLib type
21 system inherit from <type><link linkend="GObject">GObject</link></type> which is why it is important to understand
22 the details of how it works.
25 <sect1 id="gobject-instanciation">
26 <title>Object instanciation</title>
29 The <function><link linkend="g-object-new">g_object_new</link></function> family of functions can be used to instantiate any
30 GType which inherits from the GObject base type. All these functions make sure the class
31 and instance structures have been correctly initialized by glib's type system and
32 then invoke at one point or another the constructor class method which is used to:
35 Allocate and clear memory through <function><link linkend="g-type-create-instance">g_type_create_instance</link></function>,
38 Initialize the object' instance with the construction properties.
41 Although one can expect all class and instance members (except the fields
42 pointing to the parents) to be set to zero, some consider it good practice to explicitly set them.
46 Objects which inherit from GObject are allowed to override this constructor class method:
47 they should however chain to their parent constructor method before doing so:
49 GObject* (*constructor) (GType type,
50 guint n_construct_properties,
51 GObjectConstructParam *construct_properties);
56 The example below shows how <type>MamanBar</type> overrides the parent's constructor:
58 #define MAMAN_TYPE_BAR (maman_bar_get_type ())
59 #define MAMAN_BAR(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), MAMAN_TYPE_BAR, MamanBar))
60 #define MAMAN_BAR_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST ((klass), MAMAN_TYPE_BAR, MamanBarClass))
61 #define MAMAN_IS_BAR(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), MAMAN_TYPE_BAR))
62 #define MAMAN_IS_BAR_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), MAMAN_TYPE_BAR))
63 #define MAMAN_BAR_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS ((obj), MAMAN_TYPE_BAR, MamanBarClass))
65 typedef struct _MamanBar MamanBar;
66 typedef struct _MamanBarClass MamanBarClass;
70 /* instance members */
73 struct _MamanBarClass {
79 /* used by MAMAN_TYPE_BAR */
80 GType maman_bar_get_type (void);
83 maman_bar_constructor (GType type,
84 guint n_construct_properties,
85 GObjectConstructParam *construct_properties)
90 /* Invoke parent constructor. */
92 GObjectClass *parent_class;
93 klass = MAMAN_BAR_CLASS (g_type_class_peek (MAMAN_TYPE_BAR));
94 parent_class = G_OBJECT_CLASS (g_type_class_peek_parent (klass));
95 obj = parent_class->constructor (type,
96 n_construct_properties,
97 construct_properties);
106 maman_bar_instance_init (GTypeInstance *instance,
109 MamanBar *self = (MamanBar *)instance;
114 maman_bar_class_init (gpointer g_class,
115 gpointer g_class_data)
117 GObjectClass *gobject_class = G_OBJECT_CLASS (g_class);
118 MamanBarClass *klass = MAMAN_BAR_CLASS (g_class);
120 gobject_class->constructor = maman_bar_constructor;
123 GType maman_bar_get_type (void)
125 static GType type = 0;
127 static const GTypeInfo info = {
128 sizeof (MamanBarClass),
129 NULL, /* base_init */
130 NULL, /* base_finalize */
131 maman_bar_class_init, /* class_init */
132 NULL, /* class_finalize */
133 NULL, /* class_data */
136 maman_bar_instance_init /* instance_init */
138 type = g_type_register_static (G_TYPE_OBJECT,
145 If the user instantiates an object <type>MamanBar</type> with:
147 MamanBar *bar = g_object_new (MAMAN_TYPE_BAR, NULL);
149 If this is the first instantiation of such an object, the <function>maman_b_class_init</function>
150 function will be invoked after any <function>maman_b_base_class_init</function> function.
151 This will make sure the class structure of this new object is correctly initialized. Here,
152 <function>maman_bar_class_init</function> is expected to override the object's class methods
153 and setup the class' own methods. In the example above, the constructor method is the only
154 overridden method: it is set to <function>maman_bar_constructor</function>.
158 Once <function><link linkend="g-object-new">g_object_new</link></function> has obtained a reference to an initialized
159 class structure, it invokes its constructor method to create an instance of the new
160 object. Since it has just been overridden by <function>maman_bar_class_init</function>
161 to <function>maman_bar_constructor</function>, the latter is called and, because it
162 was implemented correctly, it chains up to its parent's constructor. The problem here
163 is how we can find the parent constructor. An approach (used in GTK+ source code) would be
164 to save the original constructor in a static variable from <function>maman_bar_class_init</function>
165 and then to re-use it from <function>maman_bar_constructor</function>. This is clearly possible
166 and very simple but I was told it was not nice and the prefered way is to use the
167 <function><link linkend="g-type-class-peek">g_type_class_peek</link></function> and <function><link linkend="g-type-class-peek-parent">g_type_class_peek_parent</link></function> functions.
171 Finally, at one point or another, <function>g_object_constructor</function> is invoked
172 by the last constructor in the chain. This function allocates the object's instance' buffer
173 through <function><link linkend="g-type-create-instance">g_type_create_instance</link></function>
174 which means that the instance_init function is invoked at this point if one
175 was registered. After instance_init returns, the object is fully initialized and should be
176 ready to answer any user-request. When <function><link linkend="g-type-create-instance">g_type_create_instance</link></function>
177 returns, <function>g_object_constructor</function> sets the construction properties
178 (ie: the properties which were given to <function><link linkend="g-object-new">g_object_new</link></function>) and returns
179 to the user's constructor which is then allowed to do useful instance initialization...
183 The process described above might seem a bit complicated (it <emphasis>is</emphasis> actually
184 overly complicated in my opinion..) but it can be summarized easily by the table below which
185 lists the functions invoked by <function><link linkend="g-object-new">g_object_new</link></function> and their order of
190 The array below lists the functions invoked by <function><link linkend="g-object-new">g_object_new</link></function> and
191 their order of invocation:
193 <table id="gobject-construction-table">
194 <title><function><link linkend="g-object-new">g_object_new</link></function></title>
196 <colspec colwidth="*" colnum="1" align="left"/>
197 <colspec colwidth="*" colnum="2" align="left"/>
198 <colspec colwidth="8*" colnum="3" align="left"/>
202 <entry>Invocation time</entry>
203 <entry>Function Invoked</entry>
204 <entry>Function's parameters</entry>
205 <entry>Remark</entry>
210 <entry>First call to <function><link linkend="g-object-new">g_object_new</link></function> for target type</entry>
211 <entry>target type's base_init function</entry>
212 <entry>On the inheritance tree of classes from fundamental type to target type.
213 base_init is invoked once for each class structure.</entry>
215 I have no real idea on how this can be used. If you have a good real-life
216 example of how a class' base_init can be used, please, let me know.
220 <entry>First call to <function><link linkend="g-object-new">g_object_new</link></function> for target type</entry>
221 <entry>target type's class_init function</entry>
222 <entry>On target type's class structure</entry>
224 Here, you should make sure to initialize or override class methods (that is,
225 assign to each class' method its function pointer) and create the signals and
226 the properties associated to your object.
230 <entry>First call to <function><link linkend="g-object-new">g_object_new</link></function> for target type</entry>
231 <entry>interface' base_init function</entry>
232 <entry>On interface' vtable</entry>
236 <entry>First call to <function><link linkend="g-object-new">g_object_new</link></function> for target type</entry>
237 <entry>interface' interface_init function</entry>
238 <entry>On interface' vtable</entry>
242 <entry>Each call to <function><link linkend="g-object-new">g_object_new</link></function> for target type</entry>
243 <entry>target type's class constructor method: GObjectClass->constructor</entry>
244 <entry>On object's instance</entry>
246 If you need to complete the object initialization after all the construction properties
247 are set, override the constructor method and make sure to chain up to the object's
248 parent class before doing your own initialization.
249 In doubt, do not override the constructor method.
253 <entry>Each call to <function><link linkend="g-object-new">g_object_new</link></function> for target type</entry>
254 <entry>type's instance_init function</entry>
255 <entry>On the inheritance tree of classes from fundamental type to target type.
256 the instance_init provided for each type is invoked once for each instance
259 Provide an instance_init function to initialize your object before its construction
260 properties are set. This is the preferred way to initialize a GObject instance.
261 This function is equivalent to C++ constructors.
270 Readers should feel concerned about one little twist in the order in which functions
271 are invoked: while, technically, the class' constructor method is called
272 <emphasis>before</emphasis> the GType's instance_init function (since
273 <function><link linkend="g-type-create-instance">g_type_create_instance</link></function> which calls instance_init is called by
274 <function>g_object_constructor</function> which is the top-level class
275 constructor method and to which users are expected to chain to), the user's code
276 which runs in a user-provided constructor will always run <emphasis>after</emphasis>
277 GType's instance_init function since the user-provided constructor
278 <emphasis>must</emphasis> (you've been warned) chain up <emphasis>before</emphasis>
279 doing anything useful.
283 <sect1 id="gobject-memory">
284 <title>Object memory management</title>
287 The memory-management API for GObjects is a bit complicated but the idea behind it
288 is pretty simple: the goal is to provide a flexible model based on reference counting
289 which can be integrated in applications which use or require different memory management
290 models (such as garbage collection, aso...). The methods which are used to
291 manipulate this reference count are described below.
296 gpointer g_object_ref (gpointer object);
297 void g_object_unref (gpointer object);
302 typedef void (*GWeakNotify) (gpointer data,
303 GObject *where_the_object_was);
304 void g_object_weak_ref (GObject *object,
307 void g_object_weak_unref (GObject *object,
310 void g_object_add_weak_pointer (GObject *object,
311 gpointer *weak_pointer_location);
312 void g_object_remove_weak_pointer (GObject *object,
313 gpointer *weak_pointer_location);
317 void g_object_run_dispose (GObject *object);
321 <sect2 id="gobject-memory-refcount">
322 <title>Reference count</title>
325 The functions <function><link linkend="g-object-ref">g_object_ref</link></function>/<function><link linkend="g-object-unref">g_object_unref</link></function> respectively
326 increase and decrease the reference count. None of these function is thread-safe.
327 The reference count is, unsurprisingly, initialized to one by
328 <function><link linkend="g-object-new">g_object_new</link></function> which means that the caller
329 is currenly the sole owner of the newly-created reference.
330 When the reference count reaches zero, that is,
331 when <function><link linkend="g-object-unref">g_object_unref</link></function> is called by the last client holding
332 a reference to the object, the <emphasis>dispose</emphasis> and the
333 <emphasis>finalize</emphasis> class methods are invoked.
336 Finally, after <emphasis>finalize</emphasis> is invoked,
337 <function><link linkend="g-type-free-instance">g_type_free_instance</link></function> is called to free the object instance.
338 Depending on the memory allocation policy decided when the type was registered (through
339 one of the <function>g_type_register_*</function> functions), the object's instance
340 memory will be freed or returned to the object pool for this type.
341 Once the object has been freed, if it was the last instance of the type, the type's class
342 will be destroyed as described in <xref linkend="gtype-instantiable-classed"/> and
343 <xref linkend="gtype-non-instantiable-classed"/>.
347 The table below summarizes the destruction process of a GObject:
348 <table id="gobject-destruction-table">
349 <title><function><link linkend="g-object-unref">g_object_unref</link></function></title>
351 <colspec colwidth="*" colnum="1" align="left"/>
352 <colspec colwidth="*" colnum="2" align="left"/>
353 <colspec colwidth="8*" colnum="3" align="left"/>
357 <entry>Invocation time</entry>
358 <entry>Function Invoked</entry>
359 <entry>Function's parameters</entry>
360 <entry>Remark</entry>
365 <entry>Last call to <function><link linkend="g-object-unref">g_object_unref</link></function> for an instance
366 of target type</entry>
367 <entry>target type's dispose class function</entry>
368 <entry>GObject instance</entry>
370 When dispose ends, the object should not hold any reference to any other
371 member object. The object is also expected to be able to answer client
372 method invocations (with possibly an error code but no memory violation)
373 until finalize is executed. dispose can be executed more than once.
374 dispose should chain up to its parent implementation just before returning
379 <entry>Last call to <function><link linkend="g-object-unref">g_object_unref</link></function> for an instance
382 <entry>target type's finalize class function</entry>
383 <entry>GObject instance</entry>
385 Finalize is expected to complete the destruction process initiated by
386 dispose. It should complete the object's destruction. finalize will be
388 finalize should chain up to its parent implementation just before returning
390 The reason why the destruction process is split is two different phases is
391 explained in <xref linkend="gobject-memory-cycles"/>.
395 <entry>Last call to <function><link linkend="g-object-unref">g_object_unref</link></function> for the last
396 instance of target type</entry>
397 <entry>interface' interface_finalize function</entry>
398 <entry>On interface' vtable</entry>
399 <entry>Never used in practice. Unlikely you will need it.</entry>
402 <entry>Last call to <function><link linkend="g-object-unref">g_object_unref</link></function>for the last
403 instance of target type</entry>
404 <entry>interface' base_finalize function</entry>
405 <entry>On interface' vtable</entry>
406 <entry>Never used in practice. Unlikely you will need it.</entry>
409 <entry>Last call to <function><link linkend="g-object-unref">g_object_unref</link></function> for the last
410 instance of target type</entry>
411 <entry>target type's class_finalize function</entry>
412 <entry>On target type's class structure</entry>
413 <entry>Never used in practice. Unlikely you will need it.</entry>
416 <entry>Last call to <function><link linkend="g-object-unref">g_object_unref</link></function> for the last
417 instance of target type</entry>
418 <entry>type's base_finalize function</entry>
419 <entry>On the inheritance tree of classes from fundamental type to target type.
420 base_init is invoked once for each class structure.</entry>
421 <entry>Never used in practice. Unlikely you will need it.</entry>
430 <sect2 id="gobject-memory-weakref">
431 <title>Weak References</title>
434 Weak References are used to monitor object finalization:
435 <function><link linkend="g-object-weak-ref">g_object_weak_ref</link></function> adds a monitoring callback which does
436 not hold a reference to the object but which is invoked when the object runs
437 its dispose method. As such, each weak ref can be invoked more than once upon
438 object finalization (since dispose can run more than once during object
443 <function><link linkend="g-object-weak-unref">g_object_weak_unref</link></function> can be used to remove a monitoring
444 callback from the object.
448 Weak References are also used to implement <function><link linkend="g-object-add-weak-pointer">g_object_add_weak_pointer</link></function>
449 and <function><link linkend="g-object-remove-weak-pointer">g_object_remove_weak_pointer</link></function>. These functions add a weak reference
450 to the object they are applied to which makes sure to nullify the pointer given by the user
451 when object is finalized.
456 <sect2 id="gobject-memory-cycles">
457 <title>Reference counts and cycles</title>
460 Note: the following section was inspired by James Henstridge. I guess this means that
461 all praise and all curses will be directly forwarded to him.
465 GObject's memory management model was designed to be easily integrated in existing code
466 using garbage collection. This is why the destruction process is split in two phases:
467 the first phase, executed in the dispose handler is supposed to release all references
468 to other member objects. The second phase, executed by the finalize handler is supposed
469 to complete the object's destruction process. Object methods should be able to run
470 without program error (that is, without segfault :) in-between the two phases.
474 This two-step destruction process is very useful to break reference counting cycles.
475 While the detection of the cycles is up to the external code, once the cycles have been
476 detected, the external code can invoke <function><link linkend="g-object-dispose">g_object_dispose</link></function> which
477 will indeed break any existing cycles since it will run the dispose handler associated
478 to the object and thus release all references to other objects.
482 Attentive readers might now have understood one of the rules about the dispose handler
483 we stated a bit sooner: the dispose handler can be invoked multiple times. Let's say we
484 have a reference count cycle: object A references B which itself references object A.
485 Let's say we have detected the cycle and we want to destroy the two objects. One way to
486 do this would be to invoke <function><link linkend="g-object-dispose">g_object_dispose</link></function> on one of the
491 If object A releases all its references to all objects, this means it releases its
492 reference to object B. If object B was not owned by anyone else, this is its last
493 reference count which means this last unref runs B's dispose handler which, in turn,
494 releases B's reference on object A. If this is A's last reference count, this last
495 unref runs A's dispose handler which is running for the second time before
496 A's finalize handler is invoked !
500 The above example, which might seem a bit contrived can really happen if your
501 GObject's are being handled by language bindings. I would thus suggest the rules stated above
502 for object destruction are closely followed. Otherwise, <emphasis>Bad Bad Things</emphasis>
508 <sect1 id="gobject-properties">
509 <title>Object properties</title>
512 One of GObject's nice features is its generic get/set mechanism for object
513 properties. When an object
514 is instanciated, the object's class_init handler should be used to register
515 the object's properties with <function><link linkend="g-object-class-install-property">g_object_class_install_property</link></function>
516 (implemented in <filename>gobject.c</filename>).
520 The best way to understand how object properties work is by looking at a real example
523 /************************************************/
525 /************************************************/
528 MAMAN_BAR_CONSTRUCT_NAME = 1,
529 MAMAN_BAR_PAPA_NUMBER,
533 maman_bar_instance_init (GTypeInstance *instance,
536 MamanBar *self = (MamanBar *)instance;
541 maman_bar_set_property (GObject *object,
546 MamanBar *self = (MamanBar *) object;
548 switch (property_id) {
549 case MAMAN_BAR_CONSTRUCT_NAME: {
550 g_free (self->private->name);
551 self->private->name = g_value_dup_string (value);
552 g_print ("maman: %s\n",self->private->name);
555 case MAMAN_BAR_PAPA_NUMBER: {
556 self->private->papa_number = g_value_get_uchar (value);
557 g_print ("papa: %u\n",self->private->papa_number);
561 /* We don't have any other property... */
562 G_OBJECT_WARN_INVALID_PROPERTY_ID(object,property_id,pspec);
568 maman_bar_get_property (GObject *object,
573 MamanBar *self = (MamanBar *) object;
575 switch (property_id) {
576 case MAMAN_BAR_CONSTRUCT_NAME: {
577 g_value_set_string (value, self->private->name);
580 case MAMAN_BAR_PAPA_NUMBER: {
581 g_value_set_uchar (value, self->private->papa_number);
585 /* We don't have any other property... */
586 G_OBJECT_WARN_INVALID_PROPERTY_ID(object,property_id,pspec);
592 maman_bar_class_init (gpointer g_class,
593 gpointer g_class_data)
595 GObjectClass *gobject_class = G_OBJECT_CLASS (g_class);
596 MamanBarClass *klass = MAMAN_BAR_CLASS (g_class);
599 gobject_class->set_property = maman_bar_set_property;
600 gobject_class->get_property = maman_bar_get_property;
602 pspec = g_param_spec_string ("maman-name",
603 "Maman construct prop",
605 "no-name-set" /* default value */,
606 G_PARAM_CONSTRUCT_ONLY | G_PARAM_READWRITE);
607 g_object_class_install_property (gobject_class,
608 MAMAN_BAR_CONSTRUCT_NAME,
611 pspec = g_param_spec_uchar ("papa-number",
612 "Number of current Papa",
613 "Set/Get papa's number",
614 0 /* minimum value */,
615 10 /* maximum value */,
616 2 /* default value */,
618 g_object_class_install_property (gobject_class,
619 MAMAN_BAR_PAPA_NUMBER,
623 /************************************************/
625 /************************************************/
629 bar = g_object_new (MAMAN_TYPE_SUBBAR, NULL);
630 g_value_init (&val, G_TYPE_CHAR);
631 g_value_set_char (&val, 11);
632 g_object_set_property (G_OBJECT (bar), "papa-number", &val);
634 The client code just above looks simple but a lot of things happen under the hood:
638 <function><link linkend="g-object-set-property">g_object_set_property</link></function> first ensures a property
639 with this name was registered in bar's class_init handler. If so, it calls
640 <function><link linkend="object-set-property">object_set_property</link></function> which first walks the class hierarchy,
641 from bottom, most derived type, to top, fundamental type to find the class
642 which registered that property. It then tries to convert the user-provided GValue
643 into a GValue whose type if that of the associated property.
647 If the user provides a signed char GValue, as is shown
648 here, and if the object's property was registered as an unsigned int,
649 <function><link linkend="g-value-transform">g_value_transform</link></function> will try to transform the input signed char into
650 an unsigned int. Of course, the success of the transformation depends on the availability
651 of the required transform function. In practice, there will almost always be a transformation
653 <para>Its behaviour might not be what you expect but it is up to you to actually avoid
654 relying on these transformations.
657 which matches and conversion will be caried out if needed.
661 After transformation, the <type><link linkend="GValue">GValue</link></type> is validated by
662 <function><link linkend="g-param-value-validate">g_param_value_validate</link></function> which makes sure the user's
663 data stored in the <type><link linkend="GValue">GValue</link></type> matches the characteristics specified by
664 the property's <type><link linkend="GParamSpec">GParamSpec</link></type>. Here, the <type><link linkend="GParamSpec">GParamSpec</link></type> we
665 provided in class_init has a validation function which makes sure that the GValue
666 contains a value which respects the minimum and maximum bounds of the
667 <type><link linkend="GParamSpec">GParamSpec</link></type>. In the example above, the client's GValue does not
668 respect these constraints (it is set to 11, while the maximum is 10). As such, the
669 <function><link linkend="g-object-set-property">g_object_set_property</link></function> function will return with an error.
673 If the user's GValue had been set to a valid value, <function><link linkend="g-object-set-property">g_object_set_property</link></function>
674 would have proceeded with calling the object's set_property class method. Here, since our
675 implementation of Foo did override this method, the code path would jump to
676 <function>foo_set_property</function> after having retrieved from the
677 <type><link linkend="GParamSpec">GParamSpec</link></type> the <emphasis>param_id</emphasis>
680 It should be noted that the param_id used here need only to uniquely identify each
681 <type><link linkend="GParamSpec">GParamSpec</link></type> within the <type><link linkend="FooClass">FooClass</link></type> such that the switch
682 used in the set and get methods actually works. Of course, this locally-unique
683 integer is purely an optimization: it would have been possible to use a set of
684 <emphasis>if (strcmp (a, b) == 0) {} else if (strcmp (a, b) == 0) {}</emphasis> statements.
687 which had been stored by
688 <function><link linkend="g-object-class-install-property">g_object_class_install_property</link></function>.
692 Once the property has been set by the object's set_property class method, the code path
693 returns to <function><link linkend="g-object-set-property">g_object_set_property</link></function> which calls
694 <function><link linkend="g-object-notify-queue-thaw">g_object_notify_queue_thaw</link></function>. This function makes sure that
695 the "notify" signal is emitted on the object's instance with the changed property as
696 parameter unless notifications were frozen by <function><link linkend="g-object-freeze-notify">g_object_freeze_notify</link></function>.
700 <function><link linkend="g-object-thaw-notify">g_object_thaw_notify</link></function> can be used to re-enable notification of
701 property modifications through the "notify" signal. It is important to remember that
702 even if properties are changed while property change notification is frozen, the "notify"
703 signal will be emitted once for each of these changed properties as soon as the property
704 change notification is thawn: no property change is lost for the "notify" signal. Signal
705 can only be delayed by the notification freezing mechanism.
708 <sect2 id="gobject-multi-properties">
709 <title>Accessing multiple properties at once</title>
713 It is interesting to note that the <function><link linkend="g-object-set">g_object_set</link></function> and
714 <function><link linkend="g-object-set-valist">g_object_set_valist</link></function> (vararg version) functions can be used to set
715 multiple properties at once. The client code shown above can then be re-written as:
719 g_object_set (G_OBJECT (foo),
721 "maman-name", "test",
724 The code above will trigger one notify signal emission for each property modified.
728 Of course, the _get versions are also available: <function><link linkend="g-object-get">g_object_get</link></function>
729 and <function><link linkend="g-object-get-valist">g_object_get_valist</link></function> (vararg version) can be used to get numerous
734 Really attentive readers now understand how <function><link linkend="g-object-new">g_object_new</link></function>,
735 <function><link linkend="g-object-newv">g_object_newv</link></function> and <function><link linkend="g-object-new-valist">g_object_new_valist</link></function>
736 work: they parse the user-provided variable number of parameters and invoke
737 <function><link linkend="g-object-set">g_object_set</link></function> on each pair of parameters only after the object has been successfully constructed.
738 Of course, the "notify" signal will be emitted for each property set.
743 <!-- @todo tell here about how to pass use handle properties in derived classe -->