QPrivateSlotBase: add empty base class optimization

There are few slots whose lambdas are empty; most will at least
capture [this]. But there are a few in Qt examples that do, e.g. []{
qApp->quit(); }. Logging is also an example. So go the extra mile and
optimize for empty functors by inheriting from them as opposed to
storing them in a member variable.

Change-Id: I3904f10db5ebe904ba889d29c08569edd804df3b
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
index 3d52478299..599f690ab2 100644
--- a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
+++ b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
@@ -5221,7 +5221,7 @@ namespace ManyArgumentNamespace {
         }
     };
 
-    struct Funct6 {
+    struct Funct6 final {
         void operator()(const QString &a, const QString &b, const QString &c, const QString&d, const QString&e, const QString&f) {
             MANYARGUMENT_COMPARE(a); MANYARGUMENT_COMPARE(b); MANYARGUMENT_COMPARE(c);
             MANYARGUMENT_COMPARE(d); MANYARGUMENT_COMPARE(e); MANYARGUMENT_COMPARE(f);