QString/QByteArray: add lvalue and rvalue overloads of left/mid/right

The first/last/sliced API may be what we suggest users use, but the vast
majority of the installed codebase uses left/mid/right because they've
been available since time immemorial.

An additional benefit of this is to make left() and right() available as
inline methods.

Change-Id: Ifeb6206a9fa04424964bfffd1788383817ed906c
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

5 files changed, 191 insertions, 42 deletions

diff --git a/src/corelib/compat/removed_api.cpp b/src/corelib/compat/removed_api.cpp
index 5c3a587f6e..6f0bb2bf10 100644
--- a/src/corelib/compat/removed_api.cpp
+++ b/src/corelib/compat/removed_api.cpp
@@ -620,6 +620,44 @@ QStringView QXmlStreamAttributes::value(QLatin1StringView qualifiedName) const
 
 #include "qbytearray.h"
 
+QByteArray QByteArray::left(qsizetype len)  const
+{
+    if (len >= size())
+        return *this;
+    if (len < 0)
+        len = 0;
+    return QByteArray(data(), len);
+}
+
+QByteArray QByteArray::right(qsizetype len) const
+{
+    if (len >= size())
+        return *this;
+    if (len < 0)
+        len = 0;
+    return QByteArray(end() - len, len);
+}
+
+QByteArray QByteArray::mid(qsizetype pos, qsizetype len) const
+{
+    qsizetype p = pos;
+    qsizetype l = len;
+    using namespace QtPrivate;
+    switch (QContainerImplHelper::mid(size(), &p, &l)) {
+    case QContainerImplHelper::Null:
+        return QByteArray();
+    case QContainerImplHelper::Empty:
+    {
+        return QByteArray(DataPointer::fromRawData(&_empty, 0));
+    }
+    case QContainerImplHelper::Full:
+        return *this;
+    case QContainerImplHelper::Subset:
+        return QByteArray(d.data() + p, l);
+    }
+    Q_UNREACHABLE_RETURN(QByteArray());
+}
+
 #ifdef Q_CC_MSVC
 // previously inline methods, only needed for MSVC compat
 QByteArray QByteArray::first(qsizetype n) const
@@ -744,6 +782,38 @@ bool QMetaObject::invokeMethodImpl(QObject *object, QtPrivate::QSlotObjectBase *
 
 #include "qstring.h"
 
+QString QString::left(qsizetype n) const
+{
+    if (size_t(n) >= size_t(size()))
+        return *this;
+    return QString((const QChar*) d.data(), n);
+}
+
+QString QString::right(qsizetype n) const
+{
+    if (size_t(n) >= size_t(size()))
+        return *this;
+    return QString(constData() + size() - n, n);
+}
+
+QString QString::mid(qsizetype position, qsizetype n) const
+{
+    qsizetype p = position;
+    qsizetype l = n;
+    using namespace QtPrivate;
+    switch (QContainerImplHelper::mid(size(), &p, &l)) {
+    case QContainerImplHelper::Null:
+        return QString();
+    case QContainerImplHelper::Empty:
+        return QString(DataPointer::fromRawData(&_empty, 0));
+    case QContainerImplHelper::Full:
+        return *this;
+    case QContainerImplHelper::Subset:
+        return QString(constData() + p, l);
+    }
+    Q_UNREACHABLE_RETURN(QString());
+}
+
 #ifdef Q_CC_MSVC
 // previously inline methods, only needed for MSVC compat
 QString QString::first(qsizetype n) const
diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp
index 1821dd2c26..1f496bd404 100644
--- a/src/corelib/text/qbytearray.cpp
+++ b/src/corelib/text/qbytearray.cpp
@@ -3022,6 +3022,9 @@ bool QByteArray::isLower() const
 */
 
 /*!
+    \fn QByteArray QByteArray::left(qsizetype len) const &
+    \fn QByteArray QByteArray::left(qsizetype len) &&
+
     Returns a byte array that contains the first \a len bytes of this byte
     array.
 
@@ -3036,16 +3039,10 @@ bool QByteArray::isLower() const
     \sa first(), last(), startsWith(), chopped(), chop(), truncate()
 */
 
-QByteArray QByteArray::left(qsizetype len)  const
-{
-    if (len >= size())
-        return *this;
-    if (len < 0)
-        len = 0;
-    return QByteArray(data(), len);
-}
-
 /*!
+    \fn QByteArray QByteArray::right(qsizetype len) const &
+    \fn QByteArray QByteArray::right(qsizetype len) &&
+
     Returns a byte array that contains the last \a len bytes of this byte array.
 
     If you know that \a len cannot be out of bounds, use last() instead in new
@@ -3058,16 +3055,11 @@ QByteArray QByteArray::left(qsizetype len)  const
 
     \sa endsWith(), last(), first(), sliced(), chopped(), chop(), truncate()
 */
-QByteArray QByteArray::right(qsizetype len) const
-{
-    if (len >= size())
-        return *this;
-    if (len < 0)
-        len = 0;
-    return QByteArray(end() - len, len);
-}
 
 /*!
+    \fn QByteArray QByteArray::mid(qsizetype pos, qsizetype len) const &
+    \fn QByteArray QByteArray::mid(qsizetype pos, qsizetype len) &&
+
     Returns a byte array containing \a len bytes from this byte array,
     starting at position \a pos.
 
@@ -3081,7 +3073,7 @@ QByteArray QByteArray::right(qsizetype len) const
     \sa first(), last(), sliced(), chopped(), chop(), truncate()
 */
 
-QByteArray QByteArray::mid(qsizetype pos, qsizetype len) const
+QByteArray QByteArray::mid(qsizetype pos, qsizetype len) const &
 {
     qsizetype p = pos;
     qsizetype l = len;
@@ -3096,7 +3088,26 @@ QByteArray QByteArray::mid(qsizetype pos, qsizetype len) const
     case QContainerImplHelper::Full:
         return *this;
     case QContainerImplHelper::Subset:
-        return QByteArray(d.data() + p, l);
+        return sliced(p, l);
+    }
+    Q_UNREACHABLE_RETURN(QByteArray());
+}
+
+QByteArray QByteArray::mid(qsizetype pos, qsizetype len) &&
+{
+    qsizetype p = pos;
+    qsizetype l = len;
+    using namespace QtPrivate;
+    switch (QContainerImplHelper::mid(size(), &p, &l)) {
+    case QContainerImplHelper::Null:
+        return QByteArray();
+    case QContainerImplHelper::Empty:
+        resize(0);      // keep capacity if we've reserve()d
+        [[fallthrough]];
+    case QContainerImplHelper::Full:
+        return std::move(*this);
+    case QContainerImplHelper::Subset:
+        return std::move(*this).sliced(p, l);
     }
     Q_UNREACHABLE_RETURN(QByteArray());
 }
diff --git a/src/corelib/text/qbytearray.h b/src/corelib/text/qbytearray.h
index b5278dbba9..1f3316eed6 100644
--- a/src/corelib/text/qbytearray.h
+++ b/src/corelib/text/qbytearray.h
@@ -151,17 +151,43 @@ public:
 
     inline int compare(QByteArrayView a, Qt::CaseSensitivity cs = Qt::CaseSensitive) const noexcept;
 
-    [[nodiscard]] QByteArray left(qsizetype len) const;
-    [[nodiscard]] QByteArray right(qsizetype len) const;
-    [[nodiscard]] QByteArray mid(qsizetype index, qsizetype len = -1) const;
-
 #if QT_CORE_REMOVED_SINCE(6, 7)
+    QByteArray left(qsizetype len) const;
+    QByteArray right(qsizetype len) const;
+    QByteArray mid(qsizetype index, qsizetype len = -1) const;
     QByteArray first(qsizetype n) const;
     QByteArray last(qsizetype n) const;
     QByteArray sliced(qsizetype pos) const;
     QByteArray sliced(qsizetype pos, qsizetype n) const;
     QByteArray chopped(qsizetype len) const;
 #else
+    [[nodiscard]] QByteArray left(qsizetype n) const &
+    {
+        if (n >= size())
+            return *this;
+        return first(qMax(n, 0));
+    }
+    [[nodiscard]] QByteArray left(qsizetype n) &&
+    {
+        if (n >= size())
+            return std::move(*this);
+        return std::move(*this).first(qMax(n, 0));
+    }
+    [[nodiscard]] QByteArray right(qsizetype n) const &
+    {
+        if (n >= size())
+            return *this;
+        return last(qMax(n, 0));
+    }
+    [[nodiscard]] QByteArray right(qsizetype n) &&
+    {
+        if (n >= size())
+            return std::move(*this);
+        return std::move(*this).last(qMax(n, 0));
+    }
+    [[nodiscard]] QByteArray mid(qsizetype index, qsizetype len = -1) const &;
+    [[nodiscard]] QByteArray mid(qsizetype index, qsizetype len = -1) &&;
+
     [[nodiscard]] QByteArray first(qsizetype n) const &
     { verify(0, n); return sliced(0, n); }
     [[nodiscard]] QByteArray last(qsizetype n) const &
diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index b5b9af55e2..50bb047253 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -5149,6 +5149,9 @@ QString QString::section(const QRegularExpression &re, qsizetype start, qsizetyp
 #endif // QT_CONFIG(regularexpression)
 
 /*!
+    \fn QString QString::left(qsizetype n) const &
+    \fn QString QString::left(qsizetype n) &&
+
     Returns a substring that contains the \a n leftmost characters
     of the string.
 
@@ -5160,14 +5163,11 @@ QString QString::section(const QRegularExpression &re, qsizetype start, qsizetyp
 
     \sa first(), last(), startsWith(), chopped(), chop(), truncate()
 */
-QString QString::left(qsizetype n)  const
-{
-    if (size_t(n) >= size_t(size()))
-        return *this;
-    return QString((const QChar*) d.data(), n);
-}
 
 /*!
+    \fn QString QString::right(qsizetype n) const &
+    \fn QString QString::right(qsizetype n) &&
+
     Returns a substring that contains the \a n rightmost characters
     of the string.
 
@@ -5179,14 +5179,11 @@ QString QString::left(qsizetype n)  const
 
     \sa endsWith(), last(), first(), sliced(), chopped(), chop(), truncate()
 */
-QString QString::right(qsizetype n) const
-{
-    if (size_t(n) >= size_t(size()))
-        return *this;
-    return QString(constData() + size() - n, n);
-}
 
 /*!
+    \fn QString QString::mid(qsizetype position, qsizetype n) const &
+    \fn QString QString::mid(qsizetype position, qsizetype n) &&
+
     Returns a string that contains \a n characters of this string,
     starting at the specified \a position index.
 
@@ -5199,11 +5196,9 @@ QString QString::right(qsizetype n) const
     \a n is -1 (default), the function returns all characters that
     are available from the specified \a position.
 
-
     \sa first(), last(), sliced(), chopped(), chop(), truncate()
 */
-
-QString QString::mid(qsizetype position, qsizetype n) const
+QString QString::mid(qsizetype position, qsizetype n) const &
 {
     qsizetype p = position;
     qsizetype l = n;
@@ -5216,7 +5211,26 @@ QString QString::mid(qsizetype position, qsizetype n) const
     case QContainerImplHelper::Full:
         return *this;
     case QContainerImplHelper::Subset:
-        return QString(constData() + p, l);
+        return sliced(p, l);
+    }
+    Q_UNREACHABLE_RETURN(QString());
+}
+
+QString QString::mid(qsizetype position, qsizetype n) &&
+{
+    qsizetype p = position;
+    qsizetype l = n;
+    using namespace QtPrivate;
+    switch (QContainerImplHelper::mid(size(), &p, &l)) {
+    case QContainerImplHelper::Null:
+        return QString();
+    case QContainerImplHelper::Empty:
+        resize(0);      // keep capacity if we've reserve()d
+        [[fallthrough]];
+    case QContainerImplHelper::Full:
+        return std::move(*this);
+    case QContainerImplHelper::Subset:
+        return std::move(*this).sliced(p, l);
     }
     Q_UNREACHABLE_RETURN(QString());
 }
diff --git a/src/corelib/text/qstring.h b/src/corelib/text/qstring.h
index 411430a189..6ec7baf404 100644
--- a/src/corelib/text/qstring.h
+++ b/src/corelib/text/qstring.h
@@ -331,17 +331,45 @@ public:
 #if QT_CONFIG(regularexpression)
     [[nodiscard]] QString section(const QRegularExpression &re, qsizetype start, qsizetype end = -1, SectionFlags flags = SectionDefault) const;
 #endif
-    [[nodiscard]] QString left(qsizetype n) const;
-    [[nodiscard]] QString right(qsizetype n) const;
-    [[nodiscard]] QString mid(qsizetype position, qsizetype n = -1) const;
 
 #if QT_CORE_REMOVED_SINCE(6, 7)
+    QString left(qsizetype n) const;
+    QString right(qsizetype n) const;
+    QString mid(qsizetype position, qsizetype n = -1) const;
+
     QString first(qsizetype n) const;
     QString last(qsizetype n) const;
     QString sliced(qsizetype pos) const;
     QString sliced(qsizetype pos, qsizetype n) const;
     QString chopped(qsizetype n) const;
 #else
+    [[nodiscard]] QString left(qsizetype n) const &
+    {
+        if (size_t(n) >= size_t(size()))
+            return *this;
+        return first(n);
+    }
+    [[nodiscard]] QString left(qsizetype n) &&
+    {
+        if (size_t(n) >= size_t(size()))
+            return std::move(*this);
+        return std::move(*this).first(n);
+    }
+    [[nodiscard]] QString right(qsizetype n) const &
+    {
+        if (size_t(n) >= size_t(size()))
+            return *this;
+        return last(n);
+    }
+    [[nodiscard]] QString right(qsizetype n) &&
+    {
+        if (size_t(n) >= size_t(size()))
+            return std::move(*this);
+        return std::move(*this).last(n);
+    }
+    [[nodiscard]] QString mid(qsizetype position, qsizetype n = -1) const &;
+    [[nodiscard]] QString mid(qsizetype position, qsizetype n = -1) &&;
+
     [[nodiscard]] QString first(qsizetype n) const &
     { verify(0, n); return sliced(0, n); }
     [[nodiscard]] QString last(qsizetype n) const &