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docs: Add vfunc NULL checks to GObject how-to examples

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Not setting a pure vfunc is a programmer error, so can be handled with a
g_return_if_fail() rather than needing a g_warning().

https://bugzilla.gnome.org/show_bug.cgi?id=744060
This commit is contained in:
Philip Withnall 2015-02-20 13:14:08 +00:00
parent 82abb80553
commit a76242b35a
1 changed files with 28 additions and 14 deletions
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42
docs/reference/gobject/tut_howto.xml
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@ -571,9 +571,14 @@ void maman_bar_do_action (MamanBar *self, /* parameters */);
void void
maman_bar_do_action (MamanBar *self, /* parameters */) maman_bar_do_action (MamanBar *self, /* parameters */)
{ {
MamanBarClass *klass;
g_return_if_fail (MAMAN_IS_BAR (self)); g_return_if_fail (MAMAN_IS_BAR (self));
MAMAN_BAR_GET_CLASS (self)->do_action (self, /* parameters */); klass = MAMAN_BAR_GET_CLASS (self);
g_return_if_fail (klass->do_action != NULL);
klass->do_action (self, /* parameters */);
} }
</programlisting></informalexample> </programlisting></informalexample>
The code above simply redirects the <function>do_action</function> call The code above simply redirects the <function>do_action</function> call
@ -596,7 +601,7 @@ maman_bar_real_do_action_two (MamanBar *self, /* parameters */)
} }
static void static void
maman_bar_class_init (BarClass *klass) maman_bar_class_init (MamanBarClass *klass)
{ {
/* this is not necessary, except for demonstration purposes. /* this is not necessary, except for demonstration purposes.
* *
@ -611,27 +616,31 @@ maman_bar_class_init (BarClass *klass)
void void
maman_bar_do_action_one (MamanBar *self, /* parameters */) maman_bar_do_action_one (MamanBar *self, /* parameters */)
{ {
MamanBarClass *klass;
g_return_if_fail (MAMAN_IS_BAR (self)); g_return_if_fail (MAMAN_IS_BAR (self));
klass = MAMAN_BAR_GET_CLASS (self);
/* if the method is purely virtual, then it is a good idea to /* if the method is purely virtual, then it is a good idea to
* check that it has been overridden before calling it, and, * check that it has been overridden before calling it, and,
* depending on the intent of the class, either ignore it silently * depending on the intent of the class, either ignore it silently
* or warn the user. * or warn the user.
/ */
if (MAMAN_BAR_GET_CLASS (self)->do_action_one != NULL) g_return_if_fail (klass->do_action != NULL);
MAMAN_BAR_GET_CLASS (self)->do_action_one (self, /* parameters */); klass->do_action_one (self, /* parameters */);
else
g_warning ("Class '%s' does not override the mandatory "
"MamanBarClass.do_action_one() virtual function.",
G_OBJECT_TYPE_NAME (self));
} }
void void
maman_bar_do_action_two (MamanBar *self, /* parameters */) maman_bar_do_action_two (MamanBar *self, /* parameters */)
{ {
MamanBarClass *klass;
g_return_if_fail (MAMAN_IS_BAR (self)); g_return_if_fail (MAMAN_IS_BAR (self));
MAMAN_BAR_GET_CLASS (self)->do_action_two (self, /* parameters */); klass = MAMAN_BAR_GET_CLASS (self);
if (klass->do_action_two != NULL)
klass->do_action_two (self, /* parameters */);
} }
</programlisting></informalexample> </programlisting></informalexample>
</para> </para>
@ -653,6 +662,10 @@ struct _MamanBarClass
/* stuff */ /* stuff */
void (* helper_do_specific_action) (MamanBar *self, /* parameters */); void (* helper_do_specific_action) (MamanBar *self, /* parameters */);
/* Padding to allow adding up to 12 new virtual functions without
* breaking ABI. */
gpointer padding[12];
}; };
void maman_bar_do_any_action (MamanBar *self, /* parameters */); void maman_bar_do_any_action (MamanBar *self, /* parameters */);
@ -670,6 +683,8 @@ maman_bar_do_specific_action (MamanBar *self, /* parameters */)
void void
maman_bar_do_any_action (MamanBar *self, /* parameters */) maman_bar_do_any_action (MamanBar *self, /* parameters */)
{ {
g_return_if_fail (MAMAN_IS_BAR (self));
/* random code here */ /* random code here */
/* /*
@ -965,8 +980,7 @@ maman_ibaz_interface_init (MamanIbazInterface *iface)
static void static void
maman_baz_init (MamanBaz *self) maman_baz_init (MamanBaz *self)
{ {
MamanBaz *self = MAMAN_BAZ (instance); self->instance_member = 0xdeadbeef;
self->instance_member = 0xdeadbeaf;
} }
</programlisting></informalexample> </programlisting></informalexample>
</para> </para>
@ -1043,7 +1057,7 @@ maman_ibaz_interface_init (MamanIbazInterface *iface)
static void static void
maman_bar_class_init (MamanBarClass *klass) maman_bar_class_init (MamanBarClass *klass)
{ {
/* Nothing here. */
} }
static void static void
@ -1118,7 +1132,6 @@ maman_ibaz_default_init (MamanIbazInterface *iface)
The following code snippet shows the modifications needed in the The following code snippet shows the modifications needed in the
<type>MamanBaz</type> declaration and implementation above: <type>MamanBaz</type> declaration and implementation above:
<informalexample><programlisting> <informalexample><programlisting>
struct _MamanBaz struct _MamanBaz
{ {
GObject parent_instance; GObject parent_instance;
@ -1210,6 +1223,7 @@ static void
maman_derived_ibaz_do_action (MamanIbaz *ibaz) maman_derived_ibaz_do_action (MamanIbaz *ibaz)
{ {
MamanDerivedBaz *self = MAMAN_DERIVED_BAZ (ibaz); MamanDerivedBaz *self = MAMAN_DERIVED_BAZ (ibaz);
g_print ("DerivedBaz implementation of Ibaz interface Action\n"); g_print ("DerivedBaz implementation of Ibaz interface Action\n");
} }