Add serializer/deserializer for Enumeration

Enum class are serialized using the declared size.

[ChangeLog][QtCore][QDataStream] Enumerations can now
be serialized through QDataStream without the need of
manually defining streaming operators.

Change-Id: Iae9a63eb62b5a5615b657766a3c4c66ba4d98d0e
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
Reviewed-by: Paolo Dastoli <paolo.dastoli@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/serialization/qdatastream.cpp

@@ -98,6 +98,10 @@ QT_BEGIN_NAMESPACE
     ensures that you get integers of the size you want and insulates
     you from compiler and platform differences.
 
+    Enumerations can be serialized through QDataStream without the
+    need of manually defining streaming operators. Enum classes are
+    serialized using the declared size.
+
     To take one example, a \c{char *} string is written as a 32-bit
     integer equal to the length of the string including the '\\0' byte,
     followed by all the characters of the string including the

src/corelib/serialization/qdatastream.h

@@ -377,6 +377,16 @@ template <typename Enum>
 inline QDataStream &operator>>(QDataStream &s, QFlags<Enum> &e)
 { return s >> e.i; }
 
+template <typename T>
+typename std::enable_if<std::is_enum<T>::value, QDataStream &>::type&
+operator<<(QDataStream &s, const T &t)
+{ return s << static_cast<typename std::underlying_type<T>::type>(t); }
+
+template <typename T>
+typename std::enable_if<std::is_enum<T>::value, QDataStream &>::type&
+operator>>(QDataStream &s, T &t)
+{ return s >> reinterpret_cast<typename std::underlying_type<T>::type &>(t); }
+
 template <typename T>
 inline QDataStream &operator>>(QDataStream &s, QList<T> &l)
 {

tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp

@@ -181,6 +181,8 @@ private slots:
 
     void streamRealDataTypes();
 
+    void enumTest();
+
     void floatingPointPrecision();
 
     void compatibility_Qt3();
@@ -3409,6 +3411,90 @@ void tst_QDataStream::floatingPointNaN()
     }
 }
 
+void tst_QDataStream::enumTest()
+{
+    QByteArray ba;
+
+    enum class E1 : qint8
+    {
+        A,
+        B,
+        C
+    };
+    {
+        QDataStream stream(&ba, QIODevice::WriteOnly);
+        stream << E1::A;
+        QCOMPARE(ba.size(), int(sizeof(E1)));
+    }
+    {
+        QDataStream stream(ba);
+        E1 e;
+        stream >> e;
+        QCOMPARE(e, E1::A);
+    }
+    ba.clear();
+
+    enum class E2 : qint16
+    {
+        A,
+        B,
+        C
+    };
+    {
+        QDataStream stream(&ba, QIODevice::WriteOnly);
+        stream << E2::B;
+        QCOMPARE(ba.size(), int(sizeof(E2)));
+    }
+    {
+        QDataStream stream(ba);
+        E2 e;
+        stream >> e;
+        QCOMPARE(e, E2::B);
+    }
+    ba.clear();
+
+    enum class E4 : qint32
+    {
+        A,
+        B,
+        C
+    };
+    {
+        QDataStream stream(&ba, QIODevice::WriteOnly);
+        stream << E4::C;
+        QCOMPARE(ba.size(), int(sizeof(E4)));
+    }
+    {
+        QDataStream stream(ba);
+        E4 e;
+        stream >> e;
+        QCOMPARE(e, E4::C);
+    }
+    ba.clear();
+
+
+    enum E
+    {
+        A,
+        B,
+        C,
+        D
+    };
+    {
+        QDataStream stream(&ba, QIODevice::WriteOnly);
+        stream << E::D;
+        QCOMPARE(ba.size(), 4);
+    }
+    {
+        QDataStream stream(ba);
+        E e;
+        stream >> e;
+        QCOMPARE(e, E::D);
+    }
+    ba.clear();
+
+}
+
 void tst_QDataStream::floatingPointPrecision()
 {
     QByteArray ba;