[GitHub] [arrow-datafusion] alamb commented on a diff in pull request #4261: improve error messages while downcasting `UInt32Array`, `UInt64Array` and `BooleanArray`

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

alamb commented on code in PR #4261:
URL: https://github.com/apache/arrow-datafusion/pull/4261#discussion_r1026563763


##########
datafusion/common/src/cast.rs:
##########
@@ -116,3 +116,36 @@ pub fn as_string_array(array: &dyn Array) -> Result<&StringArray, DataFusionErro
         ))
     })
 }
+
+// Downcast ArrayRef to UInt32Array
+pub fn as_uint32_array(array: &dyn Array) -> Result<&UInt32Array, DataFusionError> {
+    array.as_any().downcast_ref::<UInt32Array>().ok_or_else(|| {
+        DataFusionError::Internal(format!(
+            "Expected a UInt32Array, got: {}",
+            array.data_type()
+        ))
+    })
+}
+
+// Downcast ArrayRef to UInt64Array
+pub fn as_uint64_array(array: &dyn Array) -> Result<&UInt64Array, DataFusionError> {
+    array.as_any().downcast_ref::<UInt64Array>().ok_or_else(|| {
+        DataFusionError::Internal(format!(
+            "Expected a UInt64Array, got: {}",
+            array.data_type()
+        ))
+    })
+}
+
+// Downcast ArrayRef to BooleanArray
+pub fn as_boolean_array(array: &dyn Array) -> Result<&BooleanArray, DataFusionError> {
+    array
+        .as_any()
+        .downcast_ref::<BooleanArray>()
+        .ok_or_else(|| {
+            DataFusionError::Internal(format!(
+                "Expected a BooleanArray, got: {}",
+                array.data_type()
+            ))
+        })
+}

Review Comment:
   Well, that is embarrassing 🤦 
   
   Interestingly the `downcast_value` doesn't appear to be used in that many places (around 5 at this time0:
   https://github.com/search?q=repo%3Aapache%2Farrow-datafusion+downcast_value&type=code
   
    I would prefer not to roll back the PRs as they have already simplified the code non trivially.
   
   What is important in my opinion is to use a standard pattern to do this downcasting. I don't have a huge preference between `downcast_value` and `as_boolean_array` , though the `as_boolean_array` might be more discoverable in an IDE that autocompletes
   
   If we are worried about code duplication, perhaps we can use `downcast_value` to implement the `as_boolean_array`, type methods



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