QByteArray: add STL-style assign()

Implemented assign() methods for QByteArray to align with the
criteria of std::basic_string, addressing the previously missing
functionality. This is a subset of the overloads provided by the
standard.

Reference:
https://en.cppreference.com/w/cpp/string/basic_string/assign

[ChangeLog][QtCore][QByteArray] Added assign().

Fixes: QTBUG-106199
Change-Id: I899b14d74e8f774face8690303efb8610ead95b5
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/corelib/text/qbytearray.cpp

@@ -2104,6 +2104,73 @@ QByteArray& QByteArray::append(char ch)
     return *this;
 }
 
+/*!
+    \fn QByteArray &QByteArray::assign(QByteArrayView v)
+    \since 6.6
+
+    Replaces the contents of this byte array with a copy of \a v and returns a
+    reference to this byte array.
+
+    The size of this byte array will be equal to the size of \a v.
+
+    This function only allocates memory if the size of \a v exceeds the capacity
+    of this byte array or this byte array is shared.
+*/
+
+/*!
+    \fn QByteArray &QByteArray::assign(qsizetype n, char c)
+    \since 6.6
+
+    Replaces the contents of this byte array with \a n copies of \a c and
+    returns a reference to this byte array.
+
+    The size of this byte array will be equal to \a n, which has to be non-negative.
+
+    This function will only allocate memory if \a n exceeds the capacity of this
+    byte array or this byte array is shared.
+
+    \sa fill()
+*/
+
+/*!
+    \fn template <typename InputIterator, if_input_iterator<InputIterator>> QByteArray &QByteArray::assign(InputIterator first, InputIterator last)
+    \since 6.6
+
+    Replaces the contents of this byte array with a copy of the elements in the
+    iterator range [\a first, \a last) and returns a reference to this
+    byte array.
+
+    The size of this byte array will be equal to the number of elements in the
+    range [\a first, \a last).
+
+    This function will only allocate memory if the number of elements in the
+    range exceeds the capacity of this byte array or this byte array is shared.
+
+    \note This function overload only participates in overload resolution if
+    \c InputIterator meets the requirements of a
+    \l {https://en.cppreference.com/w/cpp/named_req/InputIterator} {LegacyInputIterator}.
+
+    \note The behavior is undefined if either argument is an iterator into *this or
+    [\a first, \a last) is not a valid range.
+*/
+
+QByteArray &QByteArray::assign(QByteArrayView v)
+{
+    const auto len = v.size();
+
+    if (len <= capacity() &&  isDetached()) {
+        const auto offset = d.freeSpaceAtBegin();
+        if (offset)
+            d.setBegin(d.begin() - offset);
+        std::memcpy(d.begin(), v.data(), len);
+        d.size = len;
+        d.data()[d.size] = '\0';
+    } else {
+        *this = v.toByteArray();
+    }
+    return *this;
+}
+
 /*!
     Inserts \a data at index position \a i and returns a
     reference to this byte array.

src/corelib/text/qbytearray.h

@@ -40,6 +40,8 @@ namespace emscripten {
 }
 #endif
 
+class tst_QByteArray;
+
 QT_BEGIN_NAMESPACE
 
 class QString;
@@ -60,6 +62,11 @@ private:
 
     DataPointer d;
     static const char _empty;
+
+    friend class ::tst_QByteArray;
+
+    template <typename InputIterator>
+    using if_input_iterator = QtPrivate::IfIsInputIterator<InputIterator>;
 public:
 
     enum Base64Option {
@@ -227,6 +234,20 @@ public:
     QByteArray &append(QByteArrayView a)
     { return insert(size(), a); }
 
+    QByteArray &assign(QByteArrayView v);
+    QByteArray &assign(qsizetype n, char c)
+    {
+        Q_ASSERT(n >= 0);
+        return fill(c, n);
+    }
+    template <typename InputIterator, if_input_iterator<InputIterator> = true>
+    QByteArray &assign(InputIterator first, InputIterator last)
+    {
+        d.assign(first, last);
+        d.data()[d.size] = '\0';
+        return *this;
+    }
+
     QByteArray &insert(qsizetype i, QByteArrayView data);
     inline QByteArray &insert(qsizetype i, const char *s)
     { return insert(i, QByteArrayView(s)); }

tests/auto/corelib/text/qbytearray/tst_qbytearray.cpp

@@ -12,6 +12,9 @@
 
 #include "../shared/test_number_shared.h"
 
+#include <QtCore/q20iterator.h>
+#include <sstream>
+
 using namespace Qt::StringLiterals;
 
 class tst_QByteArray : public QObject
@@ -50,6 +53,9 @@ private slots:
     void append();
     void appendExtended_data();
     void appendExtended();
+    void assign();
+    void assignShared();
+    void assignUsesPrependBuffer();
     void insert();
     void insertExtended_data();
     void insertExtended();
@@ -930,6 +936,190 @@ void tst_QByteArray::appendExtended()
     QCOMPARE(array.size(), 11);
 }
 
+void tst_QByteArray::assign()
+{
+    // QByteArray &assign(QByteArrayView)
+    {
+        QByteArray ba;
+        QByteArray test("data");
+        QCOMPARE(ba.assign(test), test);
+        QCOMPARE(ba.size(), test.size());
+        test = "data\0data";
+        QCOMPARE(ba.assign(test), test);
+        QCOMPARE(ba.size(), test.size());
+        test = "data\0data"_ba;
+        QCOMPARE(ba.assign(test), test);
+        QCOMPARE(ba.size(), test.size());
+    }
+    // QByteArray &assign(qsizetype, char);
+    {
+        QByteArray ba;
+        QByteArray test("ddd");
+        QCOMPARE(ba.assign(3, 'd'), test);
+        QCOMPARE(ba.size(), test.size());
+        test = "xx";
+        QCOMPARE(ba.assign(20, 'd').assign(2, 'x'), test);
+        QCOMPARE(ba.size(), test.size());
+        test = "ddddd";
+        QCOMPARE(ba.assign(0, 'x').assign(5, 'd'), test);
+        QCOMPARE(ba.size(), test.size());
+        test = "\0\0\0"_ba;
+        QCOMPARE(ba.assign(0, 'x').assign(3, '\0'), test);
+        QCOMPARE(ba.size(), test.size());
+    }
+    // QByteArray &assign(InputIterator, InputIterator)
+    {
+        QByteArray ba;
+        QByteArrayView test;
+
+        QList<char> l = {'\0', 'T', 'E', 'S', 'T'};
+        ba.assign(l.begin(), l.end());
+        test = "\0TEST"_ba;
+        QCOMPARE(ba, test);
+        QCOMPARE(ba.size(), test.size());
+
+        const std::byte bytes[] = {std::byte('T'), std::byte(0), std::byte('S'), std::byte('T')};
+        test = QByteArrayView::fromArray(bytes);
+        QCOMPARE(ba.assign(test.begin(), test.end()), test);
+        QCOMPARE(ba.size(), test.size());
+
+        std::stringstream ss;
+        ss << "T " << '\0' << ' ' << "S " << "T ";
+        ba.assign(std::istream_iterator<char>{ss}, std::istream_iterator<char>{});
+        test = "T\0ST"_ba;
+        QCOMPARE(ba, test);
+        QCOMPARE(ba.size(), test.size());
+    }
+    // Test chaining
+    {
+        QByteArray ba;
+        QByteArray test("TTTTT");
+        char arr[] = {'T', 'E', 'S', 'T'};
+        ba.assign(std::begin(arr), std::end(arr)).assign({"Hello World!"}).assign(5, 'T');
+        QCOMPARE(ba, test);
+        QCOMPARE(ba.size(), test.size());
+        test = "DATA";
+        QCOMPARE(ba.assign(300, 'T').assign({"DATA"}), test);
+        QCOMPARE(ba.size(), test.size());
+        test = QByteArray(arr, q20::ssize(arr));
+        QCOMPARE(ba.assign(10, 'c').assign(std::begin(arr), std::end(arr)), test);
+        QCOMPARE(ba.size(), test.size());
+        test = "TTT";
+        QCOMPARE(ba.assign("data").assign(QByteArrayView::fromArray(
+                         {std::byte('T'), std::byte('T'), std::byte('T')})), test);
+        QCOMPARE(ba.size(), test.size());
+        test = "\0data";
+        QCOMPARE(ba.assign("data").assign("\0data"), test);
+        QCOMPARE(ba.size(), test.size());
+    }
+}
+
+void tst_QByteArray::assignShared()
+{
+    {
+        QByteArray ba;
+        ba.assign({"DATA"});
+        QVERIFY(ba.isDetached());
+        QCOMPARE(ba, QByteArray("DATA"));
+
+        auto baCopy = ba;
+        QVERIFY(!ba.isDetached());
+        QVERIFY(!baCopy.isDetached());
+        QVERIFY(ba.isSharedWith(baCopy));
+        QVERIFY(baCopy.isSharedWith(ba));
+
+        ba.assign(10, 'D');
+        QVERIFY(ba.isDetached());
+        QVERIFY(baCopy.isDetached());
+        QVERIFY(!ba.isSharedWith(baCopy));
+        QVERIFY(!baCopy.isSharedWith(ba));
+        QCOMPARE(ba, QByteArray("DDDDDDDDDD"));
+        QCOMPARE(baCopy, QByteArray("DATA"));
+    }
+    {
+        QByteArray ba("START");
+        QByteArrayView bav("DATA");
+        QVERIFY(ba.isDetached());
+        QCOMPARE(ba, QByteArray("START"));
+
+        auto copyForwardIt = ba;
+        QVERIFY(!ba.isDetached());
+        QVERIFY(!copyForwardIt.isDetached());
+        QVERIFY(ba.isSharedWith(copyForwardIt));
+        QVERIFY(copyForwardIt.isSharedWith(ba));
+
+        ba.assign(bav.begin(), bav.end());
+        QVERIFY(ba.isDetached());
+        QVERIFY(copyForwardIt.isDetached());
+        QVERIFY(!ba.isSharedWith(copyForwardIt));
+        QVERIFY(!copyForwardIt.isSharedWith(ba));
+        QCOMPARE(ba, QByteArray("DATA"));
+        QCOMPARE(copyForwardIt, QByteArray("START"));
+
+        auto copyInputIt = ba;
+        QVERIFY(!ba.isDetached());
+        QVERIFY(!copyInputIt.isDetached());
+        QVERIFY(ba.isSharedWith(copyInputIt));
+        QVERIFY(copyInputIt.isSharedWith(ba));
+
+        std::stringstream ss("1 2 3 4 5 6 ");
+        ba.assign(std::istream_iterator<char>{ss}, std::istream_iterator<char>{});
+        QVERIFY(ba.isDetached());
+        QVERIFY(copyInputIt.isDetached());
+        QVERIFY(!ba.isSharedWith(copyInputIt));
+        QVERIFY(!copyInputIt.isSharedWith(ba));
+        QCOMPARE(ba, QByteArray("123456"));
+        QCOMPARE(copyInputIt, QByteArray("DATA"));
+    }
+}
+
+void tst_QByteArray::assignUsesPrependBuffer()
+{
+    const auto capBegin = [](const QByteArray &ba) {
+        return ba.begin() - ba.d.freeSpaceAtBegin();
+    };
+    const auto capEnd = [](const QByteArray &ba) {
+        return ba.end() + ba.d.freeSpaceAtEnd();
+    };
+    // QByteArray &assign(QByteArrayView)
+    {
+        QByteArray withFreeSpaceAtBegin;
+        for (int i = 0; i < 100 && withFreeSpaceAtBegin.d.freeSpaceAtBegin() < 2; ++i)
+            withFreeSpaceAtBegin.prepend("data");
+        QCOMPARE_GT(withFreeSpaceAtBegin.d.freeSpaceAtBegin(), 1);
+
+        const auto oldCapBegin = capBegin(withFreeSpaceAtBegin);
+        const auto oldCapEnd = capEnd(withFreeSpaceAtBegin);
+
+        std::string test(withFreeSpaceAtBegin.d.freeSpaceAtBegin(), 'd');
+        withFreeSpaceAtBegin.assign(test);
+
+        QCOMPARE_EQ(withFreeSpaceAtBegin.d.freeSpaceAtBegin(), 0); // we used the prepend buffer
+        QCOMPARE_EQ(capBegin(withFreeSpaceAtBegin), oldCapBegin);
+        QCOMPARE_EQ(capEnd(withFreeSpaceAtBegin), oldCapEnd);
+        QCOMPARE(withFreeSpaceAtBegin, test.data());
+    }
+    // QByteArray &assign(InputIterator, InputIterator)
+    {
+        QByteArray withFreeSpaceAtBegin;
+        for (int i = 0; i < 100 && withFreeSpaceAtBegin.d.freeSpaceAtBegin() < 2; ++i)
+            withFreeSpaceAtBegin.prepend("data");
+        QCOMPARE_GT(withFreeSpaceAtBegin.d.freeSpaceAtBegin(), 1);
+
+        const auto oldCapBegin = capBegin(withFreeSpaceAtBegin);
+        const auto oldCapEnd = capEnd(withFreeSpaceAtBegin);
+
+        std::stringstream ss;
+        for (qsizetype i = 0; i < withFreeSpaceAtBegin.d.freeSpaceAtBegin(); ++i)
+            ss << "d ";
+
+        withFreeSpaceAtBegin.assign(std::istream_iterator<char>{ss}, std::istream_iterator<char>{});
+        QCOMPARE_EQ(withFreeSpaceAtBegin.d.freeSpaceAtBegin(), 0); // we used the prepend buffer
+        QCOMPARE_EQ(capBegin(withFreeSpaceAtBegin), oldCapBegin);
+        QCOMPARE_EQ(capEnd(withFreeSpaceAtBegin), oldCapEnd);
+    }
+}
+
 void tst_QByteArray::insert()
 {
     const char data[] = "data";

tests/auto/corelib/tools/containerapisymmetry/tst_containerapisymmetry.cpp

@@ -339,6 +339,7 @@ private Q_SLOTS:
     void assign_std_vector() { assign_impl<std::vector<int>>(); };
     void assign_QVarLengthArray() { assign_impl<QVarLengthArray<int, 4>>(); };
     void assign_QList() { assign_impl<QList<int>>(); }
+    void assign_QByteArray() { assign_impl<QByteArray>(); }
 
 private:
     template <typename Container>