qscopedvaluerollback: add convenience constructor

It's a common need to assign a variable to something when entering a
code block, and then revert it upon exit. qscopedvaluerollback can
be used for this. But as a convenience, this patch adds an
extra constructor so that you can "protect" and set a variable
in one go instead of using two lines.

Change-Id: If4b89d3a5ba32ef2304bda058b1b6050932612ed
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

3 files changed, 23 insertions, 3 deletions

diff --git a/src/corelib/tools/qscopedvaluerollback.cpp b/src/corelib/tools/qscopedvaluerollback.cpp
index 3201a3c87a..f37a232985 100644
--- a/src/corelib/tools/qscopedvaluerollback.cpp
+++ b/src/corelib/tools/qscopedvaluerollback.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
 ** Contact: http://www.qt-project.org/legal
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -70,6 +70,15 @@ QT_BEGIN_NAMESPACE
 */
 
 /*!
+    \fn QScopedValueRollback::QScopedValueRollback(T &var, T value)
+
+    Assigns \a value to \ var and stores the previous value of \a var
+    internally, for revert on destruction.
+
+    \since 5.4
+*/
+
+/*!
     \fn QScopedValueRollback::~QScopedValueRollback()
 
     Assigns the previous value to the managed variable.
diff --git a/src/corelib/tools/qscopedvaluerollback.h b/src/corelib/tools/qscopedvaluerollback.h
index dfaf1984be..2a5bd8c223 100644
--- a/src/corelib/tools/qscopedvaluerollback.h
+++ b/src/corelib/tools/qscopedvaluerollback.h
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
 ** Contact: http://www.qt-project.org/legal
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -56,6 +56,13 @@ public:
         oldValue = varRef;
     }
 
+    explicit QScopedValueRollback(T &var, T value) :
+        varRef(var)
+    {
+        oldValue = varRef;
+        varRef = value;
+    }
+
     ~QScopedValueRollback()
     {
         varRef = oldValue;
diff --git a/tests/auto/corelib/tools/qscopedvaluerollback/tst_qscopedvaluerollback.cpp b/tests/auto/corelib/tools/qscopedvaluerollback/tst_qscopedvaluerollback.cpp
index af82897179..86438caed6 100644
--- a/tests/auto/corelib/tools/qscopedvaluerollback/tst_qscopedvaluerollback.cpp
+++ b/tests/auto/corelib/tools/qscopedvaluerollback/tst_qscopedvaluerollback.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
 ** Contact: http://www.qt-project.org/legal
 **
 ** This file is part of the test suite of the Qt Toolkit.
@@ -67,14 +67,17 @@ void tst_QScopedValueRollback::leavingScope()
 {
     int i = 0;
     bool b = false;
+    bool b2 = false;
     QString s("This is useful");
 
     //test rollback on going out of scope
     {
         QScopedValueRollback<int> ri(i);
         QScopedValueRollback<bool> rb(b);
+        QScopedValueRollback<bool> rb2(b2, true);
         QScopedValueRollback<QString> rs(s);
         QCOMPARE(b, false);
+        QCOMPARE(b2, true);
         QCOMPARE(i, 0);
         QCOMPARE(s, QString("This is useful"));
         b = true;
@@ -85,6 +88,7 @@ void tst_QScopedValueRollback::leavingScope()
         QCOMPARE(s, QString("Useless"));
     }
     QCOMPARE(b, false);
+    QCOMPARE(b2, false);
     QCOMPARE(i, 0);
     QCOMPARE(s, QString("This is useful"));
 }