Reverse iterators rework (#217)

Author: tfpf

src/pysorteddict/sorted_dict_view_type.cc

@@ -57,7 +57,11 @@ void SortedDictViewIterType<RevIterType>::track(RevIterType it)
     }
     if (it != this->sd->map->rend())
     {
-        ++it->second.known_referrers;
+        FwdIterType it_base = it.base();
+        if (it_base != this->sd->map->end())
+        {
+            ++it_base->second.known_referrers;
+        }
     }
     else
     {
@@ -68,20 +72,39 @@ void SortedDictViewIterType<RevIterType>::track(RevIterType it)
 }
 
 /**
- * Do all the necessary bookkeeping required to stop tracking the given
+ * Do all the necessary bookkeeping required to stop tracking the given forward
  * iterator of the underlying sorted dictionary.
  *
  * The caller should ensure that this method is called immediately after the
  * iterator member is updated.
  *
  * @param it Previous value of the iterator member.
  */
-template<typename T>
-void SortedDictViewIterType<T>::untrack(T it)
+template<>
+void SortedDictViewIterType<FwdIterType>::untrack(FwdIterType it)
 {
     --it->second.known_referrers;
 }
 
+/**
+ * Do all the necessary bookkeeping required to stop tracking the given reverse
+ * iterator of the underlying sorted dictionary.
+ *
+ * The caller should ensure that this method is called immediately after the
+ * iterator member is updated.
+ *
+ * @param it Previous value of the iterator member.
+ */
+template<>
+void SortedDictViewIterType<RevIterType>::untrack(RevIterType it)
+{
+    FwdIterType it_base = it.base();
+    if (it_base != this->sd->map->end())
+    {
+        --it_base->second.known_referrers;
+    }
+}
+
 template<typename T>
 void SortedDictViewIterType<T>::Delete(PyObject* self)
 {

tests/functional/test_keys_iter.py

@@ -73,3 +73,18 @@ def test_destructive_forward_iteration(sorted_dict):
         del sorted_dict[key]
     assert len(sorted_dict) == 0
     assert not [*sorted_dict]
+
+
+@pytest.mark.parametrize("sorted_dict", [*range(10), 100, 1_000, 10_000, 100_000], indirect=True)
+def test_destructive_reverse_iteration(sorted_dict):
+    prev_key = None
+    for key in reversed(sorted_dict):
+        # A quirk of the implementation of reverse iterators: the current key
+        # cannot be deleted.
+        if prev_key is not None:
+            del sorted_dict[prev_key]
+        prev_key = key
+    if prev_key is not None:
+        del sorted_dict[prev_key]
+    assert len(sorted_dict) == 0
+    assert not [*sorted_dict]