From 02f6b21bbc4f1f7afc30a87227c3a0787a5d2225 Mon Sep 17 00:00:00 2001
From: Olivier Goffart <ogoffart@woboq.com>
Date: Thu, 23 Apr 2015 12:02:40 +0200
Subject: QMetaType: Fix compilation with non default constructible Q_GADGET

Do not try to automatically register the meta type for Q_GADGET that
are not default constructible.
This fixes a source incompatibility in the function pointer syntax
of QObject::connect when such types are used as an argument of a signal.

Task-number: QTBUG-45721
Change-Id: I3065f6d57bc1f37e16988d2dee99118de250ca56
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/global/qtypetraits.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

(limited to 'src/corelib/global')

diff --git a/src/corelib/global/qtypetraits.h b/src/corelib/global/qtypetraits.h
index 3a305713e6..488e257e0f 100644
--- a/src/corelib/global/qtypetraits.h
+++ b/src/corelib/global/qtypetraits.h
@@ -506,6 +506,27 @@ Q_STATIC_ASSERT((!is_unsigned<qint64>::value));
 Q_STATIC_ASSERT((!is_signed<quint64>::value));
 Q_STATIC_ASSERT(( is_signed<qint64>::value));
 
+template<class T = void> struct is_default_constructible;
+
+template<> struct is_default_constructible<void>
+{
+protected:
+    template<bool> struct test { typedef char type; };
+public:
+    static bool const value = false;
+};
+template<> struct is_default_constructible<>::test<true> { typedef double type; };
+
+template<class T> struct is_default_constructible : is_default_constructible<>
+{
+private:
+    template<class U> static typename test<!!sizeof(::new U())>::type sfinae(U*);
+    template<class U> static char sfinae(...);
+public:
+    static bool const value = sizeof(sfinae<T>(0)) > 1;
+};
+
+
 } // namespace QtPrivate
 
 QT_END_NAMESPACE
-- 
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