Implement ExactSizeIterator for (Circular)TupleWindows

src/tuple_impl.rs

@@ -209,6 +209,7 @@ where
     T: TupleCollect + Clone,
 {
     iter: Take<TupleWindows<Cycle<I>, T>>,
+    len: usize,
     phantom_data: PhantomData<T>,
 }
 
@@ -223,6 +224,7 @@ where
 
     CircularTupleWindows {
         iter,
+        len,
         phantom_data: PhantomData {},
     }
 }
@@ -236,8 +238,29 @@ where
     type Item = T;
 
     fn next(&mut self) -> Option<Self::Item> {
+        self.len = self.len.saturating_sub(1);
         self.iter.next()
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len, Some(self.len))
+    }
+}
+
+impl<I, T> ExactSizeIterator for CircularTupleWindows<I, T>
+where
+    I: Iterator<Item = T::Item> + Clone,
+    T: TupleCollect + Clone,
+    T::Item: Clone,
+{
+}
+
+impl<I, T> FusedIterator for CircularTupleWindows<I, T>
+where
+    I: Iterator<Item = T::Item> + Clone,
+    T: TupleCollect + Clone,
+    T::Item: Clone,
+{
 }
 
 pub trait TupleCollect: Sized {

tests/quick.rs

@@ -1117,6 +1117,10 @@ quickcheck! {
         true
     }
 
+    fn circular_tuple_windows_exact_size(a: Vec<u8>) -> bool {
+        exact_size(a.iter().circular_tuple_windows::<(_, _, _, _)>())
+    }
+
     fn equal_tuple_windows_1(a: Vec<u8>) -> bool {
         let x = a.windows(1).map(|s| (&s[0], ));
         let y = a.iter().tuple_windows::<(_,)>();