[glibmm] VariantBase: Add operator for BoolExpr (const void*).

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 459b12d0c7cb33e503b730d84b7275e9f8cf3682
Author: Andrew Potter <agpotter gmail com>
Date:   Tue Dec 18 16:10:58 2012 +0100

    VariantBase: Add operator for BoolExpr (const void*).
    
    * glib/src/variant.{ccg,hg}: Adds operator BoolExpr.
    Also deletes relational operators to prevent unexpected conversion.
    Bug #690121.

 ChangeLog            |    8 ++++++++
 glib/src/variant.ccg |    5 +++++
 glib/src/variant.hg  |   37 +++++++++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 0 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 0ef9101..ca5bb60 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2012-12-18  Andrew Potter  <agpotter gmail com>
+
+	VariantBase: Add operator for BoolExpr (const void*).
+
+	* glib/src/variant.{ccg,hg}: Adds operator BoolExpr.
+	Also deletes relational operators to prevent unexpected conversion.
+	Bug #690121.
+
 2012-12-13  Andrew Potter  <agpotter gmail com>
 
 	SimpleAction: Fix stateful action constructor typo, allowing use.
diff --git a/glib/src/variant.ccg b/glib/src/variant.ccg
index b7f4f52..dea7391 100644
--- a/glib/src/variant.ccg
+++ b/glib/src/variant.ccg
@@ -182,6 +182,11 @@ bool VariantContainerBase::get_maybe(VariantBase& maybe) const
 
 /****************** Specializations ***********************************/
 
+VariantBase::operator const void*() const
+{
+  return gobj() ? GINT_TO_POINTER(1) : 0;
+}
+
 void VariantBase::init(const GVariant* cobject, bool take_a_reference)
 {
   if(gobject_)
diff --git a/glib/src/variant.hg b/glib/src/variant.hg
index 046b270..19e84f8 100644
--- a/glib/src/variant.hg
+++ b/glib/src/variant.hg
@@ -87,6 +87,23 @@ class VariantBase
     g_variant_get, g_variant_get_va)
 public:
 
+  /** This typedef is just to make it more obvious that
+   * our operator const void* should be used like operator bool().
+   */
+  typedef const void* BoolExpr;
+
+  /** Test whether the Variant has an underlying instance.
+   *
+   * Mimics usage of pointers:
+   * @code
+   *   if (variant)
+   *     do_something();
+   * @endcode
+   *
+   * @newin{2,36}
+   */
+   operator BoolExpr() const;
+
   /** Replace the underlying GVariant.
    * This is for use by methods that take a VariantBase& as an output
    * parameter.
@@ -175,6 +192,26 @@ public:
    template<class V_CastTo>
    static V_CastTo cast_dynamic(const VariantBase& v) throw(std::bad_cast);
 
+private:
+  /** Relational operators are deleted to prevent invalid conversion
+   * to const void*.
+   */
+  bool operator<(const VariantBase& src) const;
+
+  /// See operator<().
+  bool operator<=(const VariantBase& src) const;
+
+  /// See operator<().
+  bool operator>(const VariantBase& src) const;
+
+  /// See operator<().
+  bool operator>=(const VariantBase& src) const;
+
+  /// See operator<().
+  bool operator==(const VariantBase& src) const;
+
+  /// See operator<().
+  bool operator!=(const VariantBase& src) const;
 };
 
 template<class V_CastTo>