[glibmm] VariantBase: Add explicit operator bool().

[Murray Cumming <murrayc src gnome org>]

commit 35af42466f6b36fe222b2e7a80589ff12004b1f8
Author: Murray Cumming <murrayc murrayc com>
Date:   Sun Apr 10 13:51:53 2016 +0200

    VariantBase: Add explicit operator bool().
    
    Deprecating the operator const void*, which is no longer necessary
    with C++11.
    
    There doesn't seem to be any ambiguity, but let's see.

 glib/src/variant.ccg |    7 +++++++
 glib/src/variant.hg  |   12 ++++++++++++
 2 files changed, 19 insertions(+), 0 deletions(-)
---
diff --git a/glib/src/variant.ccg b/glib/src/variant.ccg
index bde8b4b..a95e390 100644
--- a/glib/src/variant.ccg
+++ b/glib/src/variant.ccg
@@ -249,10 +249,17 @@ VariantContainerBase::get_iter(const VariantType& container_variant_type) const
 
 /****************** Specializations ***********************************/
 
+#ifndef GLIBMM_DISABLE_DEPRECATED
 VariantBase::operator const void*() const
 {
   return gobj() ? GINT_TO_POINTER(1) : nullptr;
 }
+#endif // GLIBMM_DISABLE_DEPRECATED
+
+VariantBase::operator bool() const
+{
+  return gobj() ? GINT_TO_POINTER(1) : nullptr;
+}
 
 void
 VariantBase::init(const GVariant* cobject, bool take_a_reference)
diff --git a/glib/src/variant.hg b/glib/src/variant.hg
index c90fa55..7927a4d 100644
--- a/glib/src/variant.hg
+++ b/glib/src/variant.hg
@@ -95,8 +95,11 @@ class VariantBase
     g_variant_get, g_variant_get_va)
 public:
 
+#ifndef GLIBMM_DISABLE_DEPRECATED
   /** This typedef is just to make it more obvious that
    * our operator const void* should be used like operator bool().
+   *
+   * @deprecated Use the explicit operator bool() instead.
    */
   using BoolExpr = const void*;
 
@@ -108,9 +111,18 @@ public:
    *     do_something();
    * @endcode
    *
+   * @deprecated Use the explicit operator bool() instead.
+   *
    * @newin{2,36}
    */
    operator BoolExpr() const;
+#endif // GLIBMM_DISABLE_DEPRECATED
+
+   /** Test whether the Variant has an underlying instance.
+    *
+    * @newin{2,50}
+    */
+   explicit operator bool() const;
 
   /** Replace the underlying GVariant.
    * This is for use by methods that take a VariantBase& as an output