QVLA: Add operator= for initializer lists

Add a dedicated operator=(std::initializer_list) that
first resizes the QCLA, and then replaces the elements
one by one.

This should be usually faster than creating a temporary
QCLA and then copying it, except for the case where the
new array does not fit into the allocated stack - but this
is IMO nothing to optimize for.

Task-number: QTBUG-45041
Change-Id: I147d6d01186b1ca3c635b2c8365d8f6e638ce6fe
GPush-Base: 08de3113051e1289f0de0651ec5647c9ee6feb27
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qvarlengtharray.h

@@ -91,6 +91,15 @@ public:
         return *this;
     }
 
+#ifdef Q_COMPILER_INITIALIZER_LISTS
+    QVarLengthArray<T, Prealloc> &operator=(std::initializer_list<T> list)
+    {
+        resize(list.size());
+        std::copy(list.begin(), list.end(), this->begin());
+        return *this;
+    }
+#endif
+
     inline void removeLast() {
         Q_ASSERT(s > 0);
         realloc(s - 1, a);

src/corelib/tools/qvarlengtharray.qdoc

@@ -362,6 +362,15 @@
     Assigns \a other to this array and returns a reference to this array.
  */
 
+/*! \fn QVarLengthArray<T, Prealloc> &QVarLengthArray::operator=(std::initializer_list<T> list)
+    \since 5.5
+
+    Assigns the values of \a list to this array, and returns a reference to this array.
+
+    This constructor is only enabled if the compiler supports C++11 initializer
+    lists.
+*/
+
 /*! \fn QVarLengthArray::QVarLengthArray(const QVarLengthArray<T, Prealloc> &other)
     Constructs a copy of \a other.
  */

tests/auto/corelib/tools/qvarlengtharray/tst_qvarlengtharray.cpp

@@ -780,6 +780,7 @@ void tst_QVarLengthArray::initializeList()
     T val3(101);
     T val4(114);
 
+    // QVarLengthArray(std::initializer_list<>)
     QVarLengthArray<T> v1 {val1, val2, val3};
     QCOMPARE(v1, QVarLengthArray<T>() << val1 << val2 << val3);
     QCOMPARE(v1, (QVarLengthArray<T> {val1, val2, val3}));
@@ -791,6 +792,25 @@ void tst_QVarLengthArray::initializeList()
 
     QVarLengthArray<T> v4({});
     QCOMPARE(v4.size(), 0);
+
+    // operator=(std::initializer_list<>)
+
+    QVarLengthArray<T> v5({val2, val1});
+    v1 = { val1, val2 }; // make array smaller
+    v4 = { val1, val2 }; // make array bigger
+    v5 = { val1, val2 }; // same size
+    QCOMPARE(v1, QVarLengthArray<T>() << val1 << val2);
+    QCOMPARE(v4, v1);
+    QCOMPARE(v5, v1);
+
+    QVarLengthArray<T, 1> v6 = { val1 };
+    v6 = { val1, val2 }; // force allocation on heap
+    QCOMPARE(v6.size(), 2);
+    QCOMPARE(v6.first(), val1);
+    QCOMPARE(v6.last(), val2);
+
+    v6 = {}; // assign empty
+    QCOMPARE(v6.size(), 0);
 #else
     QSKIP("This tests requires a compiler that supports initializer lists.");
 #endif