Optimize Iterator::last() for PyList & PyTuple and Iterator::count() for PyDict, PyList, PyTuple & PySet

newsfragments/4878.added.md

@@ -0,0 +1,2 @@
+- Optimizes `last` for `BoundListIterator`, `BoundTupleIterator` and `BorrowedTupleIterator`
+- Optimizes `Iterator::count()` for `PyDict`, `PyList`, `PyTuple` & `PySet`

src/types/dict.rs

@@ -534,6 +534,14 @@ impl<'py> Iterator for BoundDictIterator<'py> {
         (len, Some(len))
     }
 
+    #[inline]
+    fn count(self) -> usize
+    where
+        Self: Sized,
+    {
+        self.len()
+    }
+
     #[inline]
     #[cfg(Py_GIL_DISABLED)]
     fn fold<B, F>(mut self, init: B, mut f: F) -> B
@@ -736,6 +744,14 @@ mod borrowed_iter {
             let len = self.len();
             (len, Some(len))
         }
+
+        #[inline]
+        fn count(self) -> usize
+        where
+            Self: Sized,
+        {
+            self.len()
+        }
     }
 
     impl ExactSizeIterator for BorrowedDictIter<'_, '_> {

src/types/frozenset.rs

@@ -237,6 +237,14 @@ impl<'py> Iterator for BoundFrozenSetIterator<'py> {
     fn size_hint(&self) -> (usize, Option<usize>) {
         (self.remaining, Some(self.remaining))
     }
+
+    #[inline]
+    fn count(self) -> usize
+    where
+        Self: Sized,
+    {
+        self.len()
+    }
 }
 
 impl ExactSizeIterator for BoundFrozenSetIterator<'_> {

src/types/list.rs

@@ -631,6 +631,22 @@ impl<'py> Iterator for BoundListIterator<'py> {
         (len, Some(len))
     }
 
+    #[inline]
+    fn count(self) -> usize
+    where
+        Self: Sized,
+    {
+        self.len()
+    }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item>
+    where
+        Self: Sized,
+    {
+        self.next_back()
+    }
+
     #[inline]
     #[cfg(all(Py_GIL_DISABLED, not(feature = "nightly")))]
     fn fold<B, F>(mut self, init: B, mut f: F) -> B

src/types/set.rs

@@ -270,6 +270,14 @@ impl<'py> Iterator for BoundSetIterator<'py> {
     fn size_hint(&self) -> (usize, Option<usize>) {
         (self.remaining, Some(self.remaining))
     }
+
+    #[inline]
+    fn count(self) -> usize
+    where
+        Self: Sized,
+    {
+        self.len()
+    }
 }
 
 impl ExactSizeIterator for BoundSetIterator<'_> {

src/types/tuple.rs

@@ -375,6 +375,22 @@ impl<'py> Iterator for BoundTupleIterator<'py> {
         let len = self.len();
         (len, Some(len))
     }
+
+    #[inline]
+    fn count(self) -> usize
+    where
+        Self: Sized,
+    {
+        self.len()
+    }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item>
+    where
+        Self: Sized,
+    {
+        self.next_back()
+    }
 }
 
 impl DoubleEndedIterator for BoundTupleIterator<'_> {
@@ -467,6 +483,22 @@ impl<'a, 'py> Iterator for BorrowedTupleIterator<'a, 'py> {
         let len = self.len();
         (len, Some(len))
     }
+
+    #[inline]
+    fn count(self) -> usize
+    where
+        Self: Sized,
+    {
+        self.len()
+    }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item>
+    where
+        Self: Sized,
+    {
+        self.next_back()
+    }
 }
 
 impl DoubleEndedIterator for BorrowedTupleIterator<'_, '_> {