QSettings: replace a QMap with a QList

The QMap<QString, QString> was only used to create a sorted,
unique list of keys. The associativeness was never used (the
value was always the null QString).

Better to use a QStringList instead and sort-unique the
whole thing at the end.

Saves ~1.6K in text size on Linux AMD64 GCC 4.9 release C++11
builds, and a tremendous amount of heap allocations.

Change-Id: Idf749dd8924b3894e436aa1cee0304002b898975
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

3 files changed, 13 insertions, 7 deletions

diff --git a/src/corelib/io/qsettings.cpp b/src/corelib/io/qsettings.cpp
index 2ae89af356..b61cba7f7d 100644
--- a/src/corelib/io/qsettings.cpp
+++ b/src/corelib/io/qsettings.cpp
@@ -299,7 +299,7 @@ QSettingsPrivate *QSettingsPrivate::create(const QString &fileName, QSettings::F
 }
 #endif
 
-void QSettingsPrivate::processChild(QStringRef key, ChildSpec spec, QMap<QString, QString> &result)
+void QSettingsPrivate::processChild(QStringRef key, ChildSpec spec, QStringList &result)
 {
     if (spec != AllKeys) {
         int slashPos = key.indexOf(QLatin1Char('/'));
@@ -312,7 +312,7 @@ void QSettingsPrivate::processChild(QStringRef key, ChildSpec spec, QMap<QString
             key.truncate(slashPos);
         }
     }
-    result.insert(key.toString(), QString());
+    result.append(key.toString());
 }
 
 void QSettingsPrivate::beginGroupOrArray(const QSettingsGroup &group)
@@ -1272,7 +1272,7 @@ bool QConfFileSettingsPrivate::get(const QString &key, QVariant *value) const
 
 QStringList QConfFileSettingsPrivate::children(const QString &prefix, ChildSpec spec) const
 {
-    QMap<QString, QString> result;
+    QStringList result;
     ParsedSettingsMap::const_iterator j;
 
     QSettingsKey thePrefix(prefix, caseSensitivity);
@@ -1307,7 +1307,10 @@ QStringList QConfFileSettingsPrivate::children(const QString &prefix, ChildSpec
                 break;
         }
     }
-    return result.keys();
+    std::sort(result.begin(), result.end());
+    result.erase(std::unique(result.begin(), result.end()),
+                 result.end());
+    return result;
 }
 
 void QConfFileSettingsPrivate::clear()
diff --git a/src/corelib/io/qsettings_mac.cpp b/src/corelib/io/qsettings_mac.cpp
index 083722869f..1ad198b990 100644
--- a/src/corelib/io/qsettings_mac.cpp
+++ b/src/corelib/io/qsettings_mac.cpp
@@ -491,7 +491,7 @@ bool QMacSettingsPrivate::get(const QString &key, QVariant *value) const
 
 QStringList QMacSettingsPrivate::children(const QString &prefix, ChildSpec spec) const
 {
-    QMap<QString, QString> result;
+    QStringList result;
     int startPos = prefix.size();
 
     for (int i = 0; i < numDomains; ++i) {
@@ -513,7 +513,10 @@ QStringList QMacSettingsPrivate::children(const QString &prefix, ChildSpec spec)
         if (!fallbacks)
             break;
     }
-    return result.keys();
+    std::sort(result.begin(), result.end());
+    result.erase(std::unique(result.begin(), result.end()),
+                 result.end());
+    return result;
 }
 
 void QMacSettingsPrivate::clear()
diff --git a/src/corelib/io/qsettings_p.h b/src/corelib/io/qsettings_p.h
index 004751182c..534527ed5a 100644
--- a/src/corelib/io/qsettings_p.h
+++ b/src/corelib/io/qsettings_p.h
@@ -211,7 +211,7 @@ public:
                                         const QString &organization, const QString &application);
     static QSettingsPrivate *create(const QString &fileName, QSettings::Format format);
 
-    static void processChild(QStringRef key, ChildSpec spec, QMap<QString, QString> &result);
+    static void processChild(QStringRef key, ChildSpec spec, QStringList &result);
 
     // Variant streaming functions
     static QStringList variantListToStringList(const QVariantList &l);