Support free functions and const functors as callbacks

Amend 207aae5560aa2865ec55ddb9ecbb50048060c0c0, as code checker
complained that we std::move'd a potential lvalue. This warning was
valid if the public API did not accept the functor parameter by value.

Fix this by consistently std::forward'ing the parameters through the
call stack, and add a compile-time test. Writing that test revealed that
the helper API didn't work with free functions, so fix that as well. It
also revealed that QFunctorSlotObject couldn't work with a const
functor, which is also fixed by this change.

We cannot support move-only functors with that change, as it requires
a change to QFunctorSlotObject that breaks the QMetaObject test.

Change-Id: Iafd747baf4cb0213ecedb391ed46b4595388182b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/network/kernel/qhostinfo.h b/src/network/kernel/qhostinfo.h
index d990af685a..9b420bd3ca 100644
--- a/src/network/kernel/qhostinfo.h
+++ b/src/network/kernel/qhostinfo.h
@@ -63,20 +63,20 @@ public:
     template <typename Functor>
     static inline int lookupHost(const QString &name,
                                  const typename QtPrivate::ContextTypeForFunctor<Functor>::ContextType *receiver,
-                                 Functor func)
+                                 Functor &&func)
     {
         using Prototype = void(*)(QHostInfo);
         return lookupHostImpl(name, receiver,
-                              QtPrivate::makeSlotObject<Prototype>(std::move(func)),
+                              QtPrivate::makeSlotObject<Prototype>(std::forward<Functor>(func)),
                               nullptr);
     }
 #endif // Q_QDOC
 
     // lookupHost to a callable (without context)
     template <typename Functor>
-    static inline int lookupHost(const QString &name, Functor slot)
+    static inline int lookupHost(const QString &name, Functor &&slot)
     {
-        return lookupHost(name, nullptr, std::move(slot));
+        return lookupHost(name, nullptr, std::forward<Functor>(slot));
     }
 
 private: