[GitHub] [arrow-rs] tustvold commented on a diff in pull request #3912: Add AsArray trait for more ergonomic downcasting

["tustvold (via GitHub)" <gi...@apache.org>]

tustvold commented on code in PR #3912:
URL: https://github.com/apache/arrow-rs/pull/3912#discussion_r1146128716


##########
arrow-array/src/cast.rs:
##########
@@ -709,6 +709,165 @@ where
     T::from(array.to_data())
 }
 
+mod private {
+    pub trait Sealed {}
+}
+
+/// An extension trait for `dyn Array` that provides ergonomic downcasting
+///
+/// ```
+/// # use std::sync::Arc;
+/// # use arrow_array::{ArrayRef, Int32Array};
+/// # use arrow_array::cast::AsArray;
+/// # use arrow_array::types::Int32Type;
+/// let col = Arc::new(Int32Array::from(vec![1, 2, 3])) as ArrayRef;
+/// assert_eq!(col.as_primitive::<Int32Type>().values(), &[1, 2, 3]);
+/// ```
+pub trait AsArray: private::Sealed {
+    /// Downcast this to a [`BooleanArray`] returning `None` if not possible
+    fn as_boolean_opt(&self) -> Option<&BooleanArray>;
+
+    /// Downcast this to a [`BooleanArray`] panicking if not possible
+    fn as_boolean(&self) -> &BooleanArray {
+        self.as_boolean_opt().expect("boolean array")
+    }
+
+    /// Downcast this to a [`PrimitiveArray`] returning `None` if not possible
+    fn as_primitive_opt<T: ArrowPrimitiveType>(&self) -> Option<&PrimitiveArray<T>>;
+
+    /// Downcast this to a [`PrimitiveArray`] panicking if not possible
+    fn as_primitive<T: ArrowPrimitiveType>(&self) -> &PrimitiveArray<T> {
+        self.as_primitive_opt().expect("primitive array")
+    }
+
+    /// Downcast this to a [`GenericByteArray`] returning `None` if not possible
+    fn as_bytes_opt<T: ByteArrayType>(&self) -> Option<&GenericByteArray<T>>;

Review Comment:
   In hindsight I probably should have called this `GenericBytesArray` but hey ho



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