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>

1 files changed, 31 insertions, 3 deletions

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 &