Impl ExactSizeIterator for IdxRange

lib/la-arena/src/lib.rs

@@ -176,9 +176,14 @@ pub fn end(&self) -> Idx<T> {
 
 impl<T> Iterator for IdxRange<T> {
     type Item = Idx<T>;
+
     fn next(&mut self) -> Option<Self::Item> {
         self.range.next().map(|raw| Idx::from_raw(raw.into()))
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.range.size_hint()
+    }
 }
 
 impl<T> DoubleEndedIterator for IdxRange<T> {
@@ -187,6 +192,8 @@ fn next_back(&mut self) -> Option<Self::Item> {
     }
 }
 
+impl<T> ExactSizeIterator for IdxRange<T> {}
+
 impl<T> fmt::Debug for IdxRange<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_tuple(&format!("IdxRange::<{}>", std::any::type_name::<T>()))