QHash/QSet: add erase(const_iterator)

This is the signature the functions have in C++11. For the std
containers, this is just convenience, but for Qt containers
with their implicit sharing problem, the combination of erase()
with constFind() can delay a detach until absolutely necessary.

[ChangeLog][QtCore][QHash/QSet] Added erase(const_iterator).

Change-Id: I2fc841c664cd7515b0f56fd7210fcd17c37f9014
Reviewed-by: David Faure <david.faure@kdab.com>

src/corelib/tools/qhash.cpp

@@ -1632,7 +1632,8 @@ uint qHash(long double key, uint seed) Q_DECL_NOTHROW
     \sa keyBegin()
 */
 
-/*! \fn QHash::iterator QHash::erase(iterator pos)
+/*! \fn QHash::iterator QHash::erase(const_iterator pos)
+    \since 5.7
 
     Removes the (key, value) pair associated with the iterator \a pos
     from the hash, and returns an iterator to the next item in the
@@ -1648,6 +1649,10 @@ uint qHash(long double key, uint seed) Q_DECL_NOTHROW
     \sa remove(), take(), find()
 */
 
+/*! \fn QHash::iterator QHash::erase(iterator pos)
+    \overload
+*/
+
 /*! \fn QHash::iterator QHash::find(const Key &key)
 
     Returns an iterator pointing to the item with the \a key in the

src/corelib/tools/qhash.h

@@ -297,6 +297,7 @@ public:
     {
         friend class const_iterator;
         friend class QHash<Key, T>;
+        friend class QSet<Key>;
         QHashData::Node *i;
 
     public:
@@ -353,6 +354,7 @@ public:
     class const_iterator
     {
         friend class iterator;
+        friend class QHash<Key, T>;
         friend class QSet<Key>;
         QHashData::Node *i;
 
@@ -450,7 +452,8 @@ public:
     inline key_iterator keyBegin() const { return key_iterator(begin()); }
     inline key_iterator keyEnd() const { return key_iterator(end()); }
 
-    iterator erase(iterator it);
+    iterator erase(iterator it) { return erase(const_iterator(it.i)); }
+    iterator erase(const_iterator it);
 
     // more Qt
     typedef iterator Iterator;
@@ -487,15 +490,18 @@ private:
 
     static void duplicateNode(QHashData::Node *originalNode, void *newNode);
 
-    bool isValidIterator(const iterator &it) const
+    bool isValidIterator(const iterator &it) const Q_DECL_NOTHROW
+    { return isValidNode(it.i); }
+    bool isValidIterator(const const_iterator &it) const Q_DECL_NOTHROW
+    { return isValidNode(it.i); }
+    bool isValidNode(QHashData::Node *node) const Q_DECL_NOTHROW
     {
 #if defined(QT_DEBUG) && !defined(Q_HASH_NO_ITERATOR_DEBUG)
-        QHashData::Node *node = it.i;
         while (node->next)
             node = node->next;
         return (static_cast<void *>(node) == d);
 #else
-        Q_UNUSED(it);
+        Q_UNUSED(node);
         return true;
 #endif
     }
@@ -807,30 +813,31 @@ Q_OUTOFLINE_TEMPLATE T QHash<Key, T>::take(const Key &akey)
 }
 
 template <class Key, class T>
-Q_OUTOFLINE_TEMPLATE typename QHash<Key, T>::iterator QHash<Key, T>::erase(iterator it)
+Q_OUTOFLINE_TEMPLATE typename QHash<Key, T>::iterator QHash<Key, T>::erase(const_iterator it)
 {
     Q_ASSERT_X(isValidIterator(it), "QHash::erase", "The specified iterator argument 'it' is invalid");
 
-    if (it == iterator(e))
-        return it;
+    if (it == const_iterator(e))
+        return iterator(it.i);
 
     if (d->ref.isShared()) {
+        // save 'it' across the detach:
         int bucketNum = (it.i->h % d->numBuckets);
-        iterator bucketIterator(*(d->buckets + bucketNum));
+        const_iterator bucketIterator(*(d->buckets + bucketNum));
         int stepsFromBucketStartToIte = 0;
         while (bucketIterator != it) {
             ++stepsFromBucketStartToIte;
             ++bucketIterator;
         }
         detach();
-        it = iterator(*(d->buckets + bucketNum));
+        it = const_iterator(*(d->buckets + bucketNum));
         while (stepsFromBucketStartToIte > 0) {
             --stepsFromBucketStartToIte;
             ++it;
         }
     }
 
-    iterator ret = it;
+    iterator ret(it.i);
     ++ret;
 
     Node *node = concrete(it.i);

src/corelib/tools/qset.h

@@ -98,6 +98,7 @@ public:
         typedef QHash<T, QHashDummyValue> Hash;
         typename Hash::iterator i;
         friend class const_iterator;
+        friend class QSet<T>;
 
     public:
         typedef std::bidirectional_iterator_tag iterator_category;
@@ -183,9 +184,11 @@ public:
     const_reverse_iterator crend() const Q_DECL_NOTHROW { return const_reverse_iterator(begin()); }
 
     iterator erase(iterator i)
+    { return erase(m2c(i)); }
+    iterator erase(const_iterator i)
     {
         Q_ASSERT_X(isValidIterator(i), "QSet::erase", "The specified const_iterator argument 'i' is invalid");
-        return q_hash.erase(reinterpret_cast<typename Hash::iterator &>(i));
+        return q_hash.erase(reinterpret_cast<typename Hash::const_iterator &>(i));
     }
 
     // more Qt
@@ -240,10 +243,18 @@ public:
 
 private:
     Hash q_hash;
+
+    static const_iterator m2c(iterator it) Q_DECL_NOTHROW
+    { return const_iterator(typename Hash::const_iterator(it.i.i)); }
+
     bool isValidIterator(const iterator &i) const
     {
         return q_hash.isValidIterator(reinterpret_cast<const typename Hash::iterator&>(i));
     }
+    bool isValidIterator(const const_iterator &i) const Q_DECL_NOTHROW
+    {
+        return q_hash.isValidIterator(reinterpret_cast<const typename Hash::const_iterator&>(i));
+    }
 };
 
 template <typename T>

src/corelib/tools/qset.qdoc

@@ -257,8 +257,8 @@
 */
 
 /*!
-    \fn QSet::iterator QSet::erase(iterator pos)
-    \since 4.2
+    \fn QSet::iterator QSet::erase(const_iterator pos)
+    \since 5.7
 
     Removes the item at the iterator position \a pos from the set, and
     returns an iterator positioned at the next item in the set.
@@ -270,6 +270,12 @@
     \sa remove(), find()
 */
 
+/*!
+    \fn QSet::iterator QSet::erase(iterator pos)
+    \since 4.2
+    \overload
+*/
+
 /*! \fn QSet::const_iterator QSet::find(const T &value) const
     \since 4.2