QMap, QHash: make key_iterator satisfy the DefaultConstructible concept

Change-Id: Ifc3f481ddb902b26c217516412c93a4a39a32b1c
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

src/corelib/tools/qhash.h

@@ -432,6 +432,7 @@ public:
         typedef const Key *pointer;
         typedef const Key &reference;
 
+        key_iterator() = default;
         explicit key_iterator(const_iterator o) : i(o) { }
 
         const Key &operator*() const { return i.key(); }

src/corelib/tools/qmap.h

@@ -531,6 +531,7 @@ public:
         typedef const Key *pointer;
         typedef const Key &reference;
 
+        key_iterator() = default;
         explicit key_iterator(const_iterator o) : i(o) { }
 
         const Key &operator*() const { return i.key(); }

tests/auto/corelib/tools/qhash/tst_qhash.cpp

@@ -1053,6 +1053,10 @@ void tst_QHash::keyIterator()
     QCOMPARE(*(--key_it), (--it).key());
 
     QCOMPARE(std::count(hash.keyBegin(), hash.keyEnd(), 99), 1);
+
+    // DefaultConstructible test
+    typedef QHash<int, int>::key_iterator keyIterator;
+    Q_STATIC_ASSERT(std::is_default_constructible<keyIterator>::value);
 }
 
 void tst_QHash::rehash_isnt_quadratic()

tests/auto/corelib/tools/qmap/tst_qmap.cpp

@@ -857,6 +857,10 @@ void tst_QMap::keyIterator()
     QCOMPARE(*(--key_it), (--it).key());
 
     QCOMPARE(std::count(map.keyBegin(), map.keyEnd(), 99), 1);
+
+    // DefaultConstructible test
+    typedef QMap<int, int>::key_iterator keyIterator;
+    Q_STATIC_ASSERT(std::is_default_constructible<keyIterator>::value);
 }
 
 void tst_QMap::keys_values_uniqueKeys()