[glibmm] Variant<>: Make this usable as an ouput parameter.

[Murray Cumming <murrayc src gnome org>]

commit 96c1f18cd3b695c925553d0ccda47da7c1d56d8c
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Jul 22 22:40:12 2010 +0200

    Variant<>: Make this usable as an ouput parameter.
    
    * glib/src/variant.[hg|ccg]: VariantBase: Added init(), like Value::init().
    This just changes the gobject_, with appropriate unref and ref.
    * gio/src/settings.[hg|ccg]: get_value(): Use an output parameter for the
    VariantBase, instead of a return value, as we do for Value, allowing the
    caller to use a derived (templated) type.
    * examples/settings/settings.cc: Show how Variant<> can be used.

 ChangeLog                     |   11 +++++++++++
 examples/settings/settings.cc |    9 ++++++++-
 gio/src/settings.ccg          |    9 +++++++++
 gio/src/settings.hg           |    6 +++++-
 glib/src/variant.ccg          |   10 ++++++++++
 glib/src/variant.hg           |    4 ++--
 6 files changed, 45 insertions(+), 4 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index df636cb..a1a78f6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,16 @@
 2010-07-22  Murray Cumming  <murrayc murrayc com>
 
+	Variant<>: Make this usable as an ouput parameter.
+
+	* glib/src/variant.[hg|ccg]: VariantBase: Added init(), like Value::init().
+	This just changes the gobject_, with appropriate unref and ref.
+	* gio/src/settings.[hg|ccg]: get_value(): Use an output parameter for the 
+	VariantBase, instead of a return value, as we do for Value, allowing the 
+	caller to use a derived (templated) type.
+	* examples/settings/settings.cc: Show how Variant<> can be used.
+
+2010-07-22  Murray Cumming  <murrayc murrayc com>
+
 	Settings example: Minor change.
 
 	* examples/settings/settings.cc: Remove the unnecessary use of 
diff --git a/examples/settings/settings.cc b/examples/settings/settings.cc
index 5f8cbfa..b7ce0ca 100644
--- a/examples/settings/settings.cc
+++ b/examples/settings/settings.cc
@@ -32,7 +32,14 @@ static void on_key_changed(const Glib::ustring& key, const Glib::RefPtr<Gio::Set
   {
     Glib::ustring str = settings->get_string(key);
     std::cout << Glib::ustring::compose("New value of '%1': '%2'\n",
-                      key, str);    
+                      key, str);
+                      
+    //Or:
+    Glib::Variant<Glib::ustring> variant;
+    settings->get_value(key, variant);
+    str = variant.get();
+    std::cout << Glib::ustring::compose("New value, via variant, of '%1': '%2'\n",
+                      key, str);
   }
   else if (key == INT_KEY)
   {
diff --git a/gio/src/settings.ccg b/gio/src/settings.ccg
index 342b70f..feaba2a 100644
--- a/gio/src/settings.ccg
+++ b/gio/src/settings.ccg
@@ -3,6 +3,15 @@
 namespace Gio
 {
 
+void Settings::get_value(const Glib::ustring& key, Glib::VariantBase& value)
+{
+  GVariant* const g_value = g_settings_get_value(gobj(), key.c_str());
+  if(!g_value)
+    return;
+
+  value.init(g_value, false /* don't take a reference */);
+}
+
 void Settings::bind(const Glib::ustring& key,
                     const Glib::PropertyProxy_Base& property_proxy,
                     SettingsBindFlags flags)
diff --git a/gio/src/settings.hg b/gio/src/settings.hg
index 9b3e457..d06b55a 100644
--- a/gio/src/settings.hg
+++ b/gio/src/settings.hg
@@ -53,7 +53,11 @@ public:
   // FIXME: implement the GVariant stuff
 
   _WRAP_METHOD(bool set_value(const Glib::ustring& key, const Glib::VariantBase& value),  g_settings_set_value)
-  _WRAP_METHOD(Glib::VariantBase get_value(const Glib::ustring& key), g_settings_get_value)
+  
+  /** TODO: Documentation.
+   */
+  void get_value(const Glib::ustring& key, Glib::VariantBase& value);
+  _IGNORE(g_settings_get_value);
 
   _WRAP_METHOD(int get_int(const Glib::ustring& key) const, g_settings_get_int)
   _WRAP_METHOD(void set_int(const Glib::ustring& key, int value), g_settings_set_int)
diff --git a/glib/src/variant.ccg b/glib/src/variant.ccg
index 9edbd4c..6f1a683 100644
--- a/glib/src/variant.ccg
+++ b/glib/src/variant.ccg
@@ -25,6 +25,16 @@ namespace Glib
 
 /****************** Specializations ***********************************/
 
+void VariantBase::init(const GVariant* cobject, bool take_a_reference)
+{
+  if(gobject_)
+    g_variant_unref(gobject_);
+
+  gobject_ = const_cast<GVariant*>(cobject);
+  if(take_a_reference)
+    g_variant_ref(gobject_);
+}
+
 // static
 const GVariantType* Variant<VariantBase>::variant_type()
 {
diff --git a/glib/src/variant.hg b/glib/src/variant.hg
index b84c50b..83306ab 100644
--- a/glib/src/variant.hg
+++ b/glib/src/variant.hg
@@ -44,13 +44,13 @@ class VariantBase
     g_variant_get, g_variant_get_va)
 public:
 
+  void init(const GVariant* cobject, bool take_a_reference = false);
+
   _WRAP_METHOD(bool is_container() const, g_variant_is_container)
   _WRAP_METHOD(GVariantClass classify() const, g_variant_classify)
   
   _WRAP_METHOD(Glib::ustring print(bool type_annotate = false) const, g_variant_print)
   _IGNORE(g_variant_print_string);
-
-  _IGNORE(g_variant_hash)
   
   #m4 _CONVERSION(`const VariantBase&',`gconstpointer',`const_cast<GVariant*>(($3).gobj())')
   _WRAP_METHOD(guint hash() const, g_variant_hash)