Properly implement qobject_cast for const pointers.

Instead of using ugly const_cast in public headers and Q_UNUSED
(which expands to nothing in release builds), use a properly-const
method.

Reviewed-By: Bradley T. Hughes
(cherry picked from commit 0b0aa7603b27447a5abe55c55d0514bc56b35f9e)

1 files changed, 19 insertions, 1 deletions

diff --git a/src/corelib/kernel/qmetaobject.cpp b/src/corelib/kernel/qmetaobject.cpp
index a70772f..ceb2a9c 100644
--- a/src/corelib/kernel/qmetaobject.cpp
+++ b/src/corelib/kernel/qmetaobject.cpp
@@ -266,7 +266,25 @@ QObject *QMetaObject::cast(QObject *obj) const
         const QMetaObject *m = obj->metaObject();
         do {
             if (m == this)
-                return const_cast<QObject*>(obj);
+                return obj;
+        } while ((m = m->d.superdata));
+    }
+    return 0;
+}
+
+/*!
+    \internal
+
+    Returns \a obj if object \a obj inherits from this
+    meta-object; otherwise returns 0.
+*/
+const QObject *QMetaObject::cast(const QObject *obj) const
+{
+    if (obj) {
+        const QMetaObject *m = obj->metaObject();
+        do {
+            if (m == this)
+                return obj;
         } while ((m = m->d.superdata));
     }
     return 0;