QSettings: port key processing to QAnyStringView

... in preparation for replacing the QString keys in the public API
with QAnyStringView ones.

This removes the "important optimization" that avoids a detach in the
common case where the input is the same as the output of
normalization. But that optimization is beside the point, because it
trades a memory allocation avoided in the library for O(N) allocations
inserted into user code for each call to QSettings::value(), the vast
majority of which are calls with string literals.

With the public interface ported to QAnyStringView in the follow-up
patch, we can then internally optimize memory allocations _in a central
place_ (e.g. by returning std::u16string or QVarLengthArray<QChar> from
normalizeKey() instead of QString). But first we need to get rid of all
the unwarranted allocations in user code.

Change-Id: I45fc83d972c552a220c9c29508001d3f172e1162
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/corelib/io/qsettings_p.h b/src/corelib/io/qsettings_p.h
index 1573a39d2a..ac82429146 100644
--- a/src/corelib/io/qsettings_p.h
+++ b/src/corelib/io/qsettings_p.h
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2022 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -209,14 +209,14 @@ public:
     virtual bool isWritable() const = 0;
     virtual QString fileName() const = 0;
 
-    QVariant value(const QString &key, const QVariant *defaultValue) const;
-    QString actualKey(const QString &key) const;
+    QVariant value(QAnyStringView key, const QVariant *defaultValue) const;
+    QString actualKey(QAnyStringView key) const;
     void beginGroupOrArray(const QSettingsGroup &group);
     void setStatus(QSettings::Status status) const;
     void requestUpdate();
     void update();
 
-    static QString normalizedKey(const QString &key);
+    static QString normalizedKey(QAnyStringView key);
     static QSettingsPrivate *create(QSettings::Format format, QSettings::Scope scope,
                                         const QString &organization, const QString &application);
     static QSettingsPrivate *create(const QString &fileName, QSettings::Format format);