QVarLengthArray/QList: make assign() return a reference to *this

While std::vector::assign() returns void, std::basic_string::assign()
returns std::basic_string&. In Qt, we want to be consistent between
{QVLA,QList,QString,QByteArray}::assign(), and returning *this is the
more general solution, so do that.

Task-number: QTBUG-106196
Task-number: QTBUG-106200
Change-Id: I2689b4af032ab6fb3f8fbcb4d825d5201ea5abeb
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/corelib/tools/qlist.h

@@ -496,18 +496,18 @@ public:
         }
     }
 
-    void assign(qsizetype n, parameter_type t)
+    QList &assign(qsizetype n, parameter_type t)
     {
         Q_ASSERT(n >= 0);
-        fill(t, n);
+        return fill(t, n);
     }
 
     template <typename InputIterator, if_input_iterator<InputIterator> = true>
-    void assign(InputIterator first, InputIterator last)
+    QList &assign(InputIterator first, InputIterator last)
-    { d.assign(first, last); }
+    { d.assign(first, last); return *this; }
 
-    void assign(std::initializer_list<T> l)
+    QList &assign(std::initializer_list<T> l)
-    { assign(l.begin(), l.end()); }
+    { return assign(l.begin(), l.end()); }
 
     template <typename ...Args>
     iterator emplace(const_iterator before, Args&&... args)

src/corelib/tools/qlist.qdoc

@@ -1538,7 +1538,7 @@
     \sa erase
 */
 
-/*! \fn template <typename T> void QList<T>::assign(qsizetype n, parameter_type t)
+/*! \fn template <typename T> QList<T>::assign(qsizetype n, parameter_type t)
     \since 6.6
 
     Replaces the contents of this list with \a n copies of \a t.
@@ -1549,7 +1549,7 @@
     list or this list is shared.
 */
 
-/*! \fn template <typename T> template <typename InputIterator, if_input_iterator<InputIterator>> void QList<T>::assign(InputIterator first, InputIterator last)
+/*! \fn template <typename T> template <typename InputIterator, if_input_iterator<InputIterator>> QList<T>::assign(InputIterator first, InputIterator last)
     \since 6.6
 
     Replaces the contents of this list with a copy of the elements in the
@@ -1569,7 +1569,7 @@
     *this.
 */
 
-/*! \fn template <typename T> void QList<T>::assign(std::initializer_list<T> l)
+/*! \fn template <typename T> QList<T>::assign(std::initializer_list<T> l)
     \since 6.6
 
     Replaces the contents of this list with a copy of the elements of

src/corelib/tools/qvarlengtharray.h

@@ -501,13 +501,13 @@ public:
     void insert(qsizetype i, const T &t);
     void insert(qsizetype i, qsizetype n, const T &t);
 
-    void assign(qsizetype n, const T &t)
+    QVarLengthArray &assign(qsizetype n, const T &t)
-    { Base::assign_impl(Prealloc, this->array, n, t); }
+    { Base::assign_impl(Prealloc, this->array, n, t); return *this; }
     template <typename InputIterator, if_input_iterator<InputIterator> = true>
-    void assign(InputIterator first, InputIterator last)
+    QVarLengthArray &assign(InputIterator first, InputIterator last)
-    { Base::assign_impl(Prealloc, this->array, first, last); }
+    { Base::assign_impl(Prealloc, this->array, first, last); return *this; }
-    void assign(std::initializer_list<T> list)
+    QVarLengthArray &assign(std::initializer_list<T> list)
-    { assign(list.begin(), list.end()); }
+    { assign(list.begin(), list.end()); return *this; }
 
 #ifdef Q_QDOC
     void replace(qsizetype i, const T &t);

src/corelib/tools/qvarlengtharray.qdoc

@@ -997,7 +997,7 @@
     \sa erase()
 */
 
-/*! \fn template <class T, qsizetype Prealloc> void QVarLengthArray<T, Prealloc>::assign(qsizetype n, const T &t)
+/*! \fn template <class T, qsizetype Prealloc> QVarLengthArray<T, Prealloc>::assign(qsizetype n, const T &t)
     \since 6.6
 
     Replaces the contents of this container with \a n copies of \a t.
@@ -1006,7 +1006,7 @@
     allocate memory if \a n exceeds the capacity of the container.
 */
 
-/*! \fn template <class T, qsizetype Prealloc> template <typename InputIterator, if_input_iterator<InputIterator>> void QVarLengthArray<T, Prealloc>::assign(InputIterator first, InputIterator last)
+/*! \fn template <class T, qsizetype Prealloc> template <typename InputIterator, if_input_iterator<InputIterator>> QVarLengthArray<T, Prealloc>::assign(InputIterator first, InputIterator last)
     \since 6.6
 
     Replaces the contents of this container with a copy of the elements in the
@@ -1023,7 +1023,7 @@
     The behavior is undefined if either argument is an iterator into *this.
 */
 
-/*! \fn template <class T, qsizetype Prealloc> void QVarLengthArray<T, Prealloc>::assign(std::initializer_list<T> list)
+/*! \fn template <class T, qsizetype Prealloc> QVarLengthArray<T, Prealloc>::assign(std::initializer_list<T> list)
     \since 6.6
 
     Replaces the contents of this container with a copy of the elements of \a list.

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

@@ -778,6 +778,18 @@ void tst_ContainerApiSymmetry::assign_impl() const
     for (const auto &e : Arr)                                \
         QCOMPARE(e, ComparisonData)                          \
     /*end*/
+#define RET_CHECK(...)                                           \
+    do {                                                         \
+        if constexpr (std::is_void_v<decltype( __VA_ARGS__ )>) { \
+            /* e.g. std::vector */                               \
+            __VA_ARGS__ ;                                        \
+        } else {                                                 \
+            /* e.g. std::basic_string */                         \
+            auto &&r = __VA_ARGS__ ;                             \
+            QCOMPARE_EQ(&r, &c);                                 \
+        }                                                        \
+    } while (false)                                              \
+    /* end */
     using V = typename Container::value_type;
     using S = typename Container::size_type;
     auto tData = V(9);
@@ -785,7 +797,7 @@ void tst_ContainerApiSymmetry::assign_impl() const
         // fill version
         auto c = make<Container>(4);
         const S oldCapacity = c.capacity();
-        c.assign(4, tData);
+        RET_CHECK(c.assign(4, tData));
         CHECK(c, tData, c.size(), S(4), c.capacity(), oldCapacity);
 
         c.assign(8, tData);
@@ -801,7 +813,7 @@ void tst_ContainerApiSymmetry::assign_impl() const
         auto iter = make<Container>(1);
 
         iter.assign(8, tData);
-        c.assign(iter.begin(), iter.end());
+        RET_CHECK(c.assign(iter.begin(), iter.end()));
         CHECK(c, tData, c.size(), S(8), c.capacity(), std::max(oldCapacity, S(8)));
 
         c.assign(iter.begin(), iter.begin());
@@ -814,7 +826,7 @@ void tst_ContainerApiSymmetry::assign_impl() const
         const S oldCapacity = c.capacity();
 
         std::stringstream ss("9 9 ");
-        c.assign(std::istream_iterator<V>{ss}, std::istream_iterator<V>{});
+        RET_CHECK(c.assign(std::istream_iterator<V>{ss}, std::istream_iterator<V>{}));
         CHECK(c, tData, c.size(), S(2), c.capacity(), oldCapacity);
 
         ss.str("");
@@ -836,10 +848,11 @@ void tst_ContainerApiSymmetry::assign_impl() const
         auto c = make<Container>(4);
         const S oldCapacity = c.capacity();
         std::initializer_list<V> list = {tData, tData, tData};
-        c.assign(list);
+        RET_CHECK(c.assign(list));
         CHECK(c, tData, c.size(), S(3), c.capacity(), oldCapacity);
     }
 
+#undef RET_CHECK
 #undef CHECK
 }