[GitHub] [arrow-rs] tustvold commented on a diff in pull request #3115: Add some initial APIs for copy-on-write support

[GitBox <gi...@apache.org>]

tustvold commented on code in PR #3115:
URL: https://github.com/apache/arrow-rs/pull/3115#discussion_r1022279925


##########
arrow-array/src/array/mod.rs:
##########
@@ -372,6 +372,28 @@ impl<'a, T: Array> Array for &'a T {
     }
 }
 
+/// A kind of `Array` which can be downcasted by `downcast_array`.
+pub(crate) trait SizedArray: AsDynAny + Array {}
+
+/// A trait used to help conversion from `Arc<Self>` to `Arc<Any>`.
+pub(crate) trait AsDynAny: Any {
+    fn as_dyn_any(self: Arc<Self>) -> Arc<dyn Any + Send + Sync + 'static>;
+}
+
+impl<T: Sized + Send + Sync + 'static> AsDynAny for T {
+    fn as_dyn_any(self: Arc<Self>) -> Arc<dyn Any + Send + Sync + 'static> {
+        self
+    }
+}
+
+/// Downcasts an Arc-ed sized `Array` to Arc-ed underlying arrow type.
+#[allow(dead_code)]
+pub(crate) fn downcast_array<T: Send + Sync + 'static>(
+    array: Arc<dyn SizedArray>,

Review Comment:
   How do you go from an `ArrayRef` to `Arc<dyn SizedArray>`?



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