Doc: Update example for connecting overloaded signas/slots

- Demonstrate qOverload(), which was added in Qt 5.7
- Replace QSignalMapper with QLCDNumber, because the former will be
  deprecated soon

Change-Id: I0d5dccb5c6fbff4b3d34d6b5a51a878bdfca7a59
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

3 files changed, 27 insertions, 18 deletions

diff --git a/doc/src/signalslotsyntaxes.qdoc b/doc/src/signalslotsyntaxes.qdoc
index 546b18c0..14400b43 100644
--- a/doc/src/signalslotsyntaxes.qdoc
+++ b/doc/src/signalslotsyntaxes.qdoc
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2014 Sze Howe Koh <szehowe.koh@gmail.com>
+** Copyright (C) 2017 Sze Howe Koh <szehowe.koh@gmail.com>
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the documentation of the Qt Toolkit.
@@ -192,16 +192,17 @@ result, the desired instance of an overloaded signal or slot is unambiguous.
 In contrast, with the functor-based syntax, an overloaded signal or slot must
 be casted to tell the compiler which instance to use.
 
-For example, \l QSignalMapper has four versions of the \c mapped() signal:
+For example, \l QLCDNumber has three versions of the \c display() slot:
 \list 1
-\li \c QSignalMapper::mapped(int)
-\li \c QSignalMapper::mapped(QString)
-\li \c QSignalMapper::mapped(QWidget*)
-\li \c QSignalMapper::mapped(QObject*)
+\li \c QLCDNumber::display(int)
+\li \c QLCDNumber::display(double)
+\li \c QLCDNumber::display(QString)
 \endlist
 
-To connect the \c int version to QSpinBox::setValue(), the two syntaxes are:
+To connect the \c int version to QSlider::valueChanged(), the two syntaxes are:
 
 \snippet snippets/signalsandslots/signalslotsyntaxes.cpp overload
 
+\sa qOverload()
+
 */
diff --git a/doc/src/snippets/signalsandslots/signalslotsyntaxes.cpp b/doc/src/snippets/signalsandslots/signalslotsyntaxes.cpp
index dbdec712..a6d9aa6f 100644
--- a/doc/src/snippets/signalsandslots/signalslotsyntaxes.cpp
+++ b/doc/src/snippets/signalsandslots/signalslotsyntaxes.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2014 Sze Howe Koh <szehowe.koh@gmail.com>
+** Copyright (C) 2017 Sze Howe Koh <szehowe.koh@gmail.com>
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the documentation of the Qt Toolkit.
@@ -136,20 +136,28 @@ DemoWidget::DemoWidget(QWidget *parent) : QWidget(parent) {
 void DemoWidget::demoOverloadConnect()
 {
 //! [overload]
-    auto mapper = new QSignalMapper(this);
-    auto spinBox = new QSpinBox(this);
+    auto slider = new QSlider(this);
+    auto lcd = new QLCDNumber(this);
 
     // String-based syntax
-    connect(mapper, SIGNAL(mapped(int)),
-            spinBox, SLOT(setValue(int)));
+    connect(slider, SIGNAL(valueChanged(int)),
+            lcd, SLOT(display(int)));
 
     // Functor-based syntax, first alternative
-    connect(mapper, static_cast<void (QSignalMapper::*)(int)>(&QSignalMapper::mapped),
-            spinBox, &QSpinBox::setValue);
+    connect(slider, &QSlider::valueChanged,
+            lcd, static_cast<void (QLCDNumber::*)(int)>(&QLCDNumber::display));
 
     // Functor-based syntax, second alternative
-    void (QSignalMapper::*mySignal)(int) = &QSignalMapper::mapped;
-    connect(mapper, mySignal,
-            spinBox, &QSpinBox::setValue);
+    void (QLCDNumber::*mySlot)(int) = &QLCDNumber::display;
+    connect(slider, &QSlider::valueChanged,
+            lcd, mySlot);
+
+    // Functor-based syntax, third alternative
+    connect(slider, &QSlider::valueChanged,
+            lcd, QOverload<int>::of(&QLCDNumber::display));
+
+    // Functor-based syntax, fourth alternative (requires C++14)
+    connect(slider, &QSlider::valueChanged,
+            lcd, qOverload<int>(&QLCDNumber::display));
 //! [overload]
 }
diff --git a/doc/src/snippets/signalsandslots/signalslotsyntaxes.pro b/doc/src/snippets/signalsandslots/signalslotsyntaxes.pro
index 1350c9f3..b3b1b9be 100644
--- a/doc/src/snippets/signalsandslots/signalslotsyntaxes.pro
+++ b/doc/src/snippets/signalsandslots/signalslotsyntaxes.pro
@@ -1,5 +1,5 @@
 QT += widgets quickwidgets multimedia
-CONFIG += c++11
+CONFIG += c++14
 HEADERS = signalslotsyntaxes.h
 SOURCES = signalslotsyntaxes.cpp
 OTHER_FILES = QmlGui.qml