Long live QStringView!

QStringView is a simple container for (const QChar*, int) and (const
char16_t*, size_t). It acts as a replacement interface type for const
QString and const QStringRef, and enables passing all kinds of
string-like types to functions otherwise expecting const QString& -
without the need to convert to QString first.

The use of this new class is guarded by a macro that enables three
levels of QStringView support:

 1. offer QStringView, overload some functions taking QString with
    QStringView

 2. like 1, but remove all overloads of functions taking QStringRef,
    leaving only the function taking QStringView.  Do this only where
    QStringRef overloads tradionally existed.

 3. like 2, but replace functions taking QString, too.

This is done in order to measure the impact of QStringView on code
size and execution speed, and to help guide the decision of which
level to choose for Qt 6.

This first patch adds QStringView with most of its planned
constructors, but not much more than iterators and isNull()/isEmpty().

Further patches will add support for QStringView to QStringBuilder,
add QStringView overloads of functions taking QString, and add the
complete API of const QString to QStringView.

[ChangeLog][QtCore][QStringView] New class, superseding const QString
and QStringRef as function parameters, accepting a wide variety of
UTF-16 string data sources, e.g. u"string", std::u16string{,_view},
and, on Windows, L"string", std::wstring{,_view} without converting to
QString first.

Change-Id: Iac273e46b2c61ec2c31b3dacebb29500599d6898
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/corelib/tools/tools.pri b/src/corelib/tools/tools.pri
index bb6c135a1a..8dd3550617 100644
--- a/src/corelib/tools/tools.pri
+++ b/src/corelib/tools/tools.pri
@@ -62,6 +62,7 @@ HEADERS +=  \
         tools/qstringiterator_p.h \
         tools/qstringlist.h \
         tools/qstringmatcher.h \
+        tools/qstringview.h \
         tools/qtextboundaryfinder.h \
         tools/qtimeline.h \
         tools/qtools_p.h \
@@ -106,6 +107,7 @@ SOURCES += \
         tools/qstring.cpp \
         tools/qstringbuilder.cpp \
         tools/qstringlist.cpp \
+        tools/qstringview.cpp \
         tools/qtextboundaryfinder.cpp \
         tools/qtimeline.cpp \
         tools/qunicodetools.cpp \