QHash/QMap: don't return const from value(), key()

... it breaks move semantics.

We can change these, since they're templates and a short survey shows
that no-one in Qt was crazy enough to inherit an exported class from
QHash or QMap.

Otherwise this would be BiC on MSVC, which encodes the return type.

There's also no safety benefit here, as none of the overloads returns
by reference, so users cannot expect map.value(key).mutate() to have
an effect on the element in the container.

In this, key() and value() differ from op[], which also returns const,
but whose overload returns a reference. op[] is therefore not proposed
here.

[ChangeLog][QtCore][QHash/QMultiHash/QMap/QMultiMap] The value() and
key() member functions now return T (was: const T), enabling move
semantics on their return values.

Change-Id: I0e5f53f9834caad458e3bde27f1daacbb4bac71b
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

4 files changed, 15 insertions, 15 deletions

diff --git a/src/corelib/tools/qhash.cpp b/src/corelib/tools/qhash.cpp
index 7ebc374d9f..1e5af7e0ce 100644
--- a/src/corelib/tools/qhash.cpp
+++ b/src/corelib/tools/qhash.cpp
@@ -1449,7 +1449,7 @@ uint qHash(long double key, uint seed) noexcept
     \sa count(), QMultiHash::contains()
 */
 
-/*! \fn template <class Key, class T> const T QHash<Key, T>::value(const Key &key) const
+/*! \fn template <class Key, class T> T QHash<Key, T>::value(const Key &key) const
 
     Returns the value associated with the \a key.
 
@@ -1461,7 +1461,7 @@ uint qHash(long double key, uint seed) noexcept
     \sa key(), values(), contains(), operator[]()
 */
 
-/*! \fn template <class Key, class T> const T QHash<Key, T>::value(const Key &key, const T &defaultValue) const
+/*! \fn template <class Key, class T> T QHash<Key, T>::value(const Key &key, const T &defaultValue) const
     \overload
 
     If the hash contains no item with the given \a key, the function returns
diff --git a/src/corelib/tools/qhash.h b/src/corelib/tools/qhash.h
index c87cf56988..d03f301306 100644
--- a/src/corelib/tools/qhash.h
+++ b/src/corelib/tools/qhash.h
@@ -298,10 +298,10 @@ public:
     T take(const Key &key);
 
     bool contains(const Key &key) const;
-    const Key key(const T &value) const;
-    const Key key(const T &value, const Key &defaultKey) const;
-    const T value(const Key &key) const;
-    const T value(const Key &key, const T &defaultValue) const;
+    Key key(const T &value) const;
+    Key key(const T &value, const Key &defaultKey) const;
+    T value(const Key &key) const;
+    T value(const Key &key, const T &defaultValue) const;
     T &operator[](const Key &key);
     const T operator[](const Key &key) const;
 
@@ -631,7 +631,7 @@ Q_INLINE_TEMPLATE QHash<Key, T> &QHash<Key, T>::operator=(const QHash &other)
 }
 
 template <class Key, class T>
-Q_INLINE_TEMPLATE const T QHash<Key, T>::value(const Key &akey) const
+Q_INLINE_TEMPLATE T QHash<Key, T>::value(const Key &akey) const
 {
     Node *node;
     if (d->size == 0 || (node = *findNode(akey)) == e) {
@@ -642,7 +642,7 @@ Q_INLINE_TEMPLATE const T QHash<Key, T>::value(const Key &akey) const
 }
 
 template <class Key, class T>
-Q_INLINE_TEMPLATE const T QHash<Key, T>::value(const Key &akey, const T &adefaultValue) const
+Q_INLINE_TEMPLATE T QHash<Key, T>::value(const Key &akey, const T &adefaultValue) const
 {
     Node *node;
     if (d->size == 0 || (node = *findNode(akey)) == e) {
@@ -679,13 +679,13 @@ Q_OUTOFLINE_TEMPLATE QList<Key> QHash<Key, T>::keys(const T &avalue) const
 }
 
 template <class Key, class T>
-Q_OUTOFLINE_TEMPLATE const Key QHash<Key, T>::key(const T &avalue) const
+Q_OUTOFLINE_TEMPLATE Key QHash<Key, T>::key(const T &avalue) const
 {
     return key(avalue, Key());
 }
 
 template <class Key, class T>
-Q_OUTOFLINE_TEMPLATE const Key QHash<Key, T>::key(const T &avalue, const Key &defaultValue) const
+Q_OUTOFLINE_TEMPLATE Key QHash<Key, T>::key(const T &avalue, const Key &defaultValue) const
 {
     const_iterator i = begin();
     while (i != end()) {
diff --git a/src/corelib/tools/qmap.cpp b/src/corelib/tools/qmap.cpp
index 25ea5f25d7..e2582ccdf4 100644
--- a/src/corelib/tools/qmap.cpp
+++ b/src/corelib/tools/qmap.cpp
@@ -704,7 +704,7 @@ void QMapDataBase::freeData(QMapDataBase *d)
     \sa count(), QMultiMap::contains()
 */
 
-/*! \fn template <class Key, class T> const T QMap<Key, T>::value(const Key &key, const T &defaultValue) const
+/*! \fn template <class Key, class T> T QMap<Key, T>::value(const Key &key, const T &defaultValue) const
 
     Returns the value associated with the key \a key.
 
diff --git a/src/corelib/tools/qmap.h b/src/corelib/tools/qmap.h
index 6081019294..be8ba6c4ba 100644
--- a/src/corelib/tools/qmap.h
+++ b/src/corelib/tools/qmap.h
@@ -364,8 +364,8 @@ public:
     T take(const Key &key);
 
     bool contains(const Key &key) const;
-    const Key key(const T &value, const Key &defaultKey = Key()) const;
-    const T value(const Key &key, const T &defaultValue = T()) const;
+    Key key(const T &value, const Key &defaultKey = Key()) const;
+    T value(const Key &key, const T &defaultValue = T()) const;
     T &operator[](const Key &key);
     const T operator[](const Key &key) const;
 
@@ -630,7 +630,7 @@ QT_WARNING_PUSH
 QT_WARNING_DISABLE_CLANG("-Wreturn-stack-address")
 
 template <class Key, class T>
-Q_INLINE_TEMPLATE const T QMap<Key, T>::value(const Key &akey, const T &adefaultValue) const
+Q_INLINE_TEMPLATE T QMap<Key, T>::value(const Key &akey, const T &adefaultValue) const
 {
     Node *n = d->findNode(akey);
     return n ? n->value : adefaultValue;
@@ -979,7 +979,7 @@ Q_OUTOFLINE_TEMPLATE QList<Key> QMap<Key, T>::keys(const T &avalue) const
 }
 
 template <class Key, class T>
-Q_OUTOFLINE_TEMPLATE const Key QMap<Key, T>::key(const T &avalue, const Key &defaultKey) const
+Q_OUTOFLINE_TEMPLATE Key QMap<Key, T>::key(const T &avalue, const Key &defaultKey) const
 {
     const_iterator i = begin();
     while (i != end()) {