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 GNOME libraries which use the GLib type system (like Gtk+ and GStreamer)
21 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 morerows="3">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 morerows="1">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.These functions are thread-safe as of GLib 2.8.
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 morerows="1">Last call to <function><link linkend="g-object-unref">g_object_unref</link></function> for an instance
368 <entry>target type's dispose class function</entry>
369 <entry>GObject instance</entry>
371 When dispose ends, the object should not hold any reference to any other
372 member object. The object is also expected to be able to answer client
373 method invocations (with possibly an error code but no memory violation)
374 until finalize is executed. dispose can be executed more than once.
375 dispose should chain up to its parent implementation just before returning
380 <!--entry>Last call to <function><link linkend="g-object-unref">g_object_unref</link></function> for an instance
383 <entry>target type's finalize class function</entry>
384 <entry>GObject instance</entry>
386 Finalize is expected to complete the destruction process initiated by
387 dispose. It should complete the object's destruction. finalize will be
389 finalize should chain up to its parent implementation just before returning
391 The reason why the destruction process is split is two different phases is
392 explained in <xref linkend="gobject-memory-cycles"/>.
396 <entry morerows="3">Last call to <function><link linkend="g-object-unref">g_object_unref</link></function> for the last
397 instance of target type
399 <entry>interface' interface_finalize function</entry>
400 <entry>On interface' vtable</entry>
401 <entry>Never used in practice. Unlikely you will need it.</entry>
404 <!--entry>Last call to <function><link linkend="g-object-unref">g_object_unref</link></function>for the last
405 instance of target type
407 <entry>interface' base_finalize function</entry>
408 <entry>On interface' vtable</entry>
409 <entry>Never used in practice. Unlikely you will need it.</entry>
412 <!--entry>Last call to <function><link linkend="g-object-unref">g_object_unref</link></function> for the last
413 instance of target type
415 <entry>target type's class_finalize function</entry>
416 <entry>On target type's class structure</entry>
417 <entry>Never used in practice. Unlikely you will need it.</entry>
420 <!--entry>Last call to <function><link linkend="g-object-unref">g_object_unref</link></function> for the last
421 instance of target type
423 <entry>type's base_finalize function</entry>
424 <entry>On the inheritance tree of classes from fundamental type to target type.
425 base_init is invoked once for each class structure.</entry>
426 <entry>Never used in practice. Unlikely you will need it.</entry>
435 <sect2 id="gobject-memory-weakref">
436 <title>Weak References</title>
439 Weak References are used to monitor object finalization:
440 <function><link linkend="g-object-weak-ref">g_object_weak_ref</link></function> adds a monitoring callback which does
441 not hold a reference to the object but which is invoked when the object runs
442 its dispose method. As such, each weak ref can be invoked more than once upon
443 object finalization (since dispose can run more than once during object
448 <function><link linkend="g-object-weak-unref">g_object_weak_unref</link></function> can be used to remove a monitoring
449 callback from the object.
453 Weak References are also used to implement <function><link linkend="g-object-add-weak-pointer">g_object_add_weak_pointer</link></function>
454 and <function><link linkend="g-object-remove-weak-pointer">g_object_remove_weak_pointer</link></function>. These functions add a weak reference
455 to the object they are applied to which makes sure to nullify the pointer given by the user
456 when object is finalized.
461 <sect2 id="gobject-memory-cycles">
462 <title>Reference counts and cycles</title>
465 Note: the following section was inspired by James Henstridge. I guess this means that
466 all praise and all curses will be directly forwarded to him.
470 GObject's memory management model was designed to be easily integrated in existing code
471 using garbage collection. This is why the destruction process is split in two phases:
472 the first phase, executed in the dispose handler is supposed to release all references
473 to other member objects. The second phase, executed by the finalize handler is supposed
474 to complete the object's destruction process. Object methods should be able to run
475 without program error (that is, without segfault :) in-between the two phases.
479 This two-step destruction process is very useful to break reference counting cycles.
480 While the detection of the cycles is up to the external code, once the cycles have been
481 detected, the external code can invoke <function><link linkend="g-object-dispose">g_object_dispose</link></function> which
482 will indeed break any existing cycles since it will run the dispose handler associated
483 to the object and thus release all references to other objects.
487 Attentive readers might now have understood one of the rules about the dispose handler
488 we stated a bit sooner: the dispose handler can be invoked multiple times. Let's say we
489 have a reference count cycle: object A references B which itself references object A.
490 Let's say we have detected the cycle and we want to destroy the two objects. One way to
491 do this would be to invoke <function><link linkend="g-object-dispose">g_object_dispose</link></function> on one of the
496 If object A releases all its references to all objects, this means it releases its
497 reference to object B. If object B was not owned by anyone else, this is its last
498 reference count which means this last unref runs B's dispose handler which, in turn,
499 releases B's reference on object A. If this is A's last reference count, this last
500 unref runs A's dispose handler which is running for the second time before
501 A's finalize handler is invoked !
505 The above example, which might seem a bit contrived can really happen if your
506 GObject's are being handled by language bindings. I would thus suggest the rules stated above
507 for object destruction are closely followed. Otherwise, <emphasis>Bad Bad Things</emphasis>
513 <sect1 id="gobject-properties">
514 <title>Object properties</title>
517 One of GObject's nice features is its generic get/set mechanism for object
518 properties. When an object
519 is instanciated, the object's class_init handler should be used to register
520 the object's properties with <function><link linkend="g-object-class-install-property">g_object_class_install_property</link></function>
521 (implemented in <filename>gobject.c</filename>).
525 The best way to understand how object properties work is by looking at a real example
528 /************************************************/
530 /************************************************/
533 MAMAN_BAR_CONSTRUCT_NAME = 1,
534 MAMAN_BAR_PAPA_NUMBER,
538 maman_bar_instance_init (GTypeInstance *instance,
541 MamanBar *self = (MamanBar *)instance;
546 maman_bar_set_property (GObject *object,
551 MamanBar *self = (MamanBar *) object;
553 switch (property_id) {
554 case MAMAN_BAR_CONSTRUCT_NAME: {
555 g_free (self->priv->name);
556 self->priv->name = g_value_dup_string (value);
557 g_print ("maman: %s\n",self->priv->name);
560 case MAMAN_BAR_PAPA_NUMBER: {
561 self->priv->papa_number = g_value_get_uchar (value);
562 g_print ("papa: %u\n",self->priv->papa_number);
566 /* We don't have any other property... */
567 G_OBJECT_WARN_INVALID_PROPERTY_ID(object,property_id,pspec);
573 maman_bar_get_property (GObject *object,
578 MamanBar *self = (MamanBar *) object;
580 switch (property_id) {
581 case MAMAN_BAR_CONSTRUCT_NAME: {
582 g_value_set_string (value, self->priv->name);
585 case MAMAN_BAR_PAPA_NUMBER: {
586 g_value_set_uchar (value, self->priv->papa_number);
590 /* We don't have any other property... */
591 G_OBJECT_WARN_INVALID_PROPERTY_ID(object,property_id,pspec);
597 maman_bar_class_init (gpointer g_class,
598 gpointer g_class_data)
600 GObjectClass *gobject_class = G_OBJECT_CLASS (g_class);
601 MamanBarClass *klass = MAMAN_BAR_CLASS (g_class);
604 gobject_class->set_property = maman_bar_set_property;
605 gobject_class->get_property = maman_bar_get_property;
607 pspec = g_param_spec_string ("maman-name",
608 "Maman construct prop",
610 "no-name-set" /* default value */,
611 G_PARAM_CONSTRUCT_ONLY | G_PARAM_READWRITE);
612 g_object_class_install_property (gobject_class,
613 MAMAN_BAR_CONSTRUCT_NAME,
616 pspec = g_param_spec_uchar ("papa-number",
617 "Number of current Papa",
618 "Set/Get papa's number",
619 0 /* minimum value */,
620 10 /* maximum value */,
621 2 /* default value */,
623 g_object_class_install_property (gobject_class,
624 MAMAN_BAR_PAPA_NUMBER,
628 /************************************************/
630 /************************************************/
634 bar = g_object_new (MAMAN_TYPE_SUBBAR, NULL);
635 g_value_init (&val, G_TYPE_CHAR);
636 g_value_set_char (&val, 11);
637 g_object_set_property (G_OBJECT (bar), "papa-number", &val);
639 The client code just above looks simple but a lot of things happen under the hood:
643 <function><link linkend="g-object-set-property">g_object_set_property</link></function> first ensures a property
644 with this name was registered in bar's class_init handler. If so, it calls
645 <function><link linkend="object-set-property">object_set_property</link></function> which first walks the class hierarchy,
646 from bottom, most derived type, to top, fundamental type to find the class
647 which registered that property. It then tries to convert the user-provided GValue
648 into a GValue whose type if that of the associated property.
652 If the user provides a signed char GValue, as is shown
653 here, and if the object's property was registered as an unsigned int,
654 <function><link linkend="g-value-transform">g_value_transform</link></function> will try to transform the input signed char into
655 an unsigned int. Of course, the success of the transformation depends on the availability
656 of the required transform function. In practice, there will almost always be a transformation
658 <para>Its behaviour might not be what you expect but it is up to you to actually avoid
659 relying on these transformations.
662 which matches and conversion will be caried out if needed.
666 After transformation, the <type><link linkend="GValue">GValue</link></type> is validated by
667 <function><link linkend="g-param-value-validate">g_param_value_validate</link></function> which makes sure the user's
668 data stored in the <type><link linkend="GValue">GValue</link></type> matches the characteristics specified by
669 the property's <type><link linkend="GParamSpec">GParamSpec</link></type>. Here, the <type><link linkend="GParamSpec">GParamSpec</link></type> we
670 provided in class_init has a validation function which makes sure that the GValue
671 contains a value which respects the minimum and maximum bounds of the
672 <type><link linkend="GParamSpec">GParamSpec</link></type>. In the example above, the client's GValue does not
673 respect these constraints (it is set to 11, while the maximum is 10). As such, the
674 <function><link linkend="g-object-set-property">g_object_set_property</link></function> function will return with an error.
678 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>
679 would have proceeded with calling the object's set_property class method. Here, since our
680 implementation of Foo did override this method, the code path would jump to
681 <function>foo_set_property</function> after having retrieved from the
682 <type><link linkend="GParamSpec">GParamSpec</link></type> the <emphasis>param_id</emphasis>
685 It should be noted that the param_id used here need only to uniquely identify each
686 <type><link linkend="GParamSpec">GParamSpec</link></type> within the <type><link linkend="FooClass">FooClass</link></type> such that the switch
687 used in the set and get methods actually works. Of course, this locally-unique
688 integer is purely an optimization: it would have been possible to use a set of
689 <emphasis>if (strcmp (a, b) == 0) {} else if (strcmp (a, b) == 0) {}</emphasis> statements.
692 which had been stored by
693 <function><link linkend="g-object-class-install-property">g_object_class_install_property</link></function>.
697 Once the property has been set by the object's set_property class method, the code path
698 returns to <function><link linkend="g-object-set-property">g_object_set_property</link></function> which calls
699 <function><link linkend="g-object-notify-queue-thaw">g_object_notify_queue_thaw</link></function>. This function makes sure that
700 the "notify" signal is emitted on the object's instance with the changed property as
701 parameter unless notifications were frozen by <function><link linkend="g-object-freeze-notify">g_object_freeze_notify</link></function>.
705 <function><link linkend="g-object-thaw-notify">g_object_thaw_notify</link></function> can be used to re-enable notification of
706 property modifications through the "notify" signal. It is important to remember that
707 even if properties are changed while property change notification is frozen, the "notify"
708 signal will be emitted once for each of these changed properties as soon as the property
709 change notification is thawn: no property change is lost for the "notify" signal. Signal
710 can only be delayed by the notification freezing mechanism.
714 It sounds like a tedious task to set up GValues everytime when one wants to modify a property.
715 In practice one will rarely do this. The functions <function><link linkend="g-object-set-property">g_object_set_property</link></function>
716 and <function><link linkend="g-object-get-property">g_object_get_property</link></function>
717 are meant to be used by language bindings. For application there is an easier way and
718 that is described next.
721 <sect2 id="gobject-multi-properties">
722 <title>Accessing multiple properties at once</title>
726 It is interesting to note that the <function><link linkend="g-object-set">g_object_set</link></function> and
727 <function><link linkend="g-object-set-valist">g_object_set_valist</link></function> (vararg version) functions can be used to set
728 multiple properties at once. The client code shown above can then be re-written as:
732 g_object_set (G_OBJECT (foo),
734 "maman-name", "test",
737 This saves us from managing the GValues that we were needing to handle when using
738 <function><link linkend="g-object-set-property">g_object_set_property</link></function>.
739 The code above will trigger one notify signal emission for each property modified.
743 Of course, the _get versions are also available: <function><link linkend="g-object-get">g_object_get</link></function>
744 and <function><link linkend="g-object-get-valist">g_object_get_valist</link></function> (vararg version) can be used to get numerous
749 These high level functions have one drawback - they don't provide a return result.
750 One should pay attention to the argument types and ranges when using them.
751 A know source of errors is to e.g. pass a gfloat instead of a gdouble and thus
752 shifting all subsequent parameters by four bytes. Also forgetting the terminating
753 NULL will lead to unexpected behaviour.
757 Really attentive readers now understand how <function><link linkend="g-object-new">g_object_new</link></function>,
758 <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>
759 work: they parse the user-provided variable number of parameters and invoke
760 <function><link linkend="g-object-set">g_object_set</link></function> on the parameters only after the object has been successfully constructed.
761 Of course, the "notify" signal will be emitted for each property set.
766 <!-- @todo tell here about how to pass use handle properties in derived classe -->