Add QMetaMethod::fromSignal() function

Given a member function that's a signal, returns the corresponding
QMetaMethod. Inspired by the implementation of the template-based
QObject::connect().

The primary use case for this function is to have an effective and
exact (not subject to shadowing) way of checking whether a known
signal was connected to in reimplementations of
QObject::connectNotify(QMetaMethod), avoiding string comparisons.
Example:

void MyObject::connectNotify(const QMetaMethod &signal)
{
    if (signal == QMetaMethod::fromSignal(&MyObject::mySignal)) {
        // Someone connected to mySignal ...
    }
}

Change-Id: I5e4de434275fe543c004d569dcaa9ceda3442f03
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/corelib/kernel/qmetaobject.h b/src/corelib/kernel/qmetaobject.h
index 5204f04ca3..1c49506926 100644
--- a/src/corelib/kernel/qmetaobject.h
+++ b/src/corelib/kernel/qmetaobject.h
@@ -141,6 +141,20 @@ public:
 
     inline bool isValid() const { return mobj != 0; }
 
+#ifdef Q_QDOC
+    static QMetaMethod fromSignal(PointerToMemberFunction signal);
+#else
+    template <typename Func>
+    static inline QMetaMethod fromSignal(Func signal)
+    {
+        typedef QtPrivate::FunctionPointer<Func> SignalType;
+        reinterpret_cast<typename SignalType::Object *>(0)->qt_check_for_QOBJECT_macro(
+                    *reinterpret_cast<typename SignalType::Object *>(0));
+        return fromSignalImpl(&SignalType::Object::staticMetaObject,
+                              reinterpret_cast<void **>(&signal));
+    }
+#endif
+
 private:
 #if QT_DEPRECATED_SINCE(5,0)
     // signature() has been renamed to methodSignature() in Qt 5.
@@ -148,6 +162,7 @@ private:
     // you convert to char*.
     char *signature(struct renamedInQt5_warning_checkTheLifeTime * = 0) Q_DECL_EQ_DELETE;
 #endif
+    static QMetaMethod fromSignalImpl(const QMetaObject *, void **);
 
     const QMetaObject *mobj;
     uint handle;