[glib/g-property: 3/10] gobject: Add override_property_default()

[Emmanuele Bassi <ebassi src gnome org>]

commit 3e8b568f20fe7aca8d614e00794bb9dd25fc7566
Author: Emmanuele Bassi <ebassi linux intel com>
Date:   Tue May 17 17:26:38 2011 +0100

    gobject: Add override_property_default()
    
    For object properties defined using the GProperty API we can easily
    override the default value from sub-classes; GObject should have a
    convenience method that does all the automagic heavy lifting so that the
    developer can just provide the property name and the new default value
    inside the class initialization function.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=648526

 gobject/gobject.c |  123 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 gobject/gobject.h |    7 +++
 2 files changed, 130 insertions(+), 0 deletions(-)
---
diff --git a/gobject/gobject.c b/gobject/gobject.c
index 494d65a..0dc8a94 100644
--- a/gobject/gobject.c
+++ b/gobject/gobject.c
@@ -793,6 +793,129 @@ g_object_class_list_properties (GObjectClass *class,
   return pspecs;
 }
 
+static inline void
+override_property_default_value (GObjectClass *oclass,
+                                 GProperty    *property,
+                                 const GValue *value)
+{
+  g_property_set_default_value (property, oclass, value);
+}
+
+/**
+ * g_object_class_override_property_default_value:
+ * @oclass: a #GObjectClass
+ * @property_name: the name of the property to override
+ * @value: a valid #GValue containing the new default value
+ *
+ * Overrides the default value of @property_name for @oclass with
+ * a new value.
+ *
+ * See g_object_class_override_property_default() for more information.
+ *
+ * This function is meant for language bindings.
+ *
+ * Since: 2.32
+ */
+void
+g_object_class_override_property_default_value (GObjectClass *oclass,
+                                                const gchar  *property_name,
+                                                const GValue *default_value)
+{
+  GParamSpec *pspec;
+
+  pspec = g_object_class_find_property (oclass, property_name);
+  if (pspec == NULL)
+    {
+      g_critical ("The class '%s' does not have a property named '%s'",
+                  g_type_name (G_OBJECT_CLASS_TYPE (oclass)),
+                  property_name);
+      return;
+    }
+
+  if (!G_IS_PROPERTY (pspec))
+    {
+      g_critical ("The property '%s' of class '%s' is of type '%s' and "
+                  "not a GProperty. Overriding the default is allowed "
+                  "only on properties defined using the GProperty API.",
+                  G_PARAM_SPEC (pspec)->name,
+                  g_type_name (G_OBJECT_CLASS_TYPE (oclass)),
+                  g_type_name (G_PARAM_SPEC_TYPE (pspec)));
+      return;
+    }
+
+  override_property_default_value (oclass, G_PROPERTY (pspec), default_value);
+}
+
+/**
+ * g_object_class_override_property_default:
+ * @oclass: a #GObjectClass
+ * @property_name: the name of the property to override
+ * @...: the new default value of the property
+ *
+ * Sets the default value of @property_name for the given #GObject
+ * class.
+ *
+ * This function can only be used with properties installed using
+ * the #GProperty API.
+ *
+ * This function is the equivalent of:
+ *
+ * |[
+ *   GParamSpec *pspec = g_object_class_find_property (oclass, property_name);
+ *
+ *   g_property_set_default (G_PROPERTY (pspec), oclass, new_value);
+ * ]|
+ *
+ * Since: 2.32
+ */
+void
+g_object_class_override_property_default (GObjectClass *oclass,
+                                          const gchar  *property_name,
+                                          ...)
+{
+  GParamSpec *pspec;
+  GValue value = { 0, };
+  va_list args;
+  gchar *error = NULL;
+
+  pspec = g_object_class_find_property (oclass, property_name);
+  if (pspec == NULL)
+    {
+      g_critical ("The class '%s' does not have a property named '%s'",
+                  g_type_name (G_OBJECT_CLASS_TYPE (oclass)),
+                  property_name);
+      return;
+    }
+
+  if (!G_IS_PROPERTY (pspec))
+    {
+      g_critical ("The property '%s' of class '%s' is of type '%s' and "
+                  "not a GProperty. Overriding the default is allowed "
+                  "only on properties defined using the GProperty API.",
+                  G_PARAM_SPEC (pspec)->name,
+                  g_type_name (G_OBJECT_CLASS_TYPE (oclass)),
+                  g_type_name (G_PARAM_SPEC_TYPE (pspec)));
+      return;
+    }
+
+  va_start (args, property_name);
+
+  G_VALUE_COLLECT_INIT (&value, G_PARAM_SPEC_VALUE_TYPE (pspec), args, 0, &error);
+  if (error != NULL)
+    {
+      g_critical (G_STRLOC ": %s", error);
+      g_free (error);
+      va_end (args);
+      return;
+    }
+
+  override_property_default_value (oclass, G_PROPERTY (pspec), &value);
+
+  g_value_unset (&value);
+
+  va_end (args);
+}
+
 /**
  * g_object_interface_list_properties:
  * @g_iface: any interface vtable for the interface, or the default
diff --git a/gobject/gobject.h b/gobject/gobject.h
index 971f365..0b1bebe 100644
--- a/gobject/gobject.h
+++ b/gobject/gobject.h
@@ -401,6 +401,13 @@ GParamSpec* g_object_interface_find_property    (gpointer     g_iface,
 GParamSpec**g_object_interface_list_properties  (gpointer     g_iface,
 						 guint       *n_properties_p);
 
+void        g_object_class_override_property_default       (GObjectClass *oclass,
+                                                            const gchar  *property_name,
+                                                            ...);
+void        g_object_class_override_property_default_value (GObjectClass *oclass,
+                                                            const gchar  *property_name,
+                                                            const GValue *default_value);
+
 GType       g_object_get_type                 (void) G_GNUC_CONST;
 gpointer    g_object_new                      (GType           object_type,
 					       const gchar    *first_property_name,