[GitHub] [arrow-datafusion] ozankabak commented on a diff in pull request #4168: Improve Error Handling and Readibility for downcasting `Decimal128Array`

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

ozankabak commented on code in PR #4168:
URL: https://github.com/apache/arrow-datafusion/pull/4168#discussion_r1019409860


##########
datafusion/common/src/scalar.rs:
##########
@@ -1881,13 +1881,22 @@ impl ScalarValue {
         index: usize,
         precision: u8,
         scale: u8,
-    ) -> ScalarValue {
-        let array = array.as_any().downcast_ref::<Decimal128Array>().unwrap();
-        if array.is_null(index) {
-            ScalarValue::Decimal128(None, precision, scale)
-        } else {
-            ScalarValue::Decimal128(Some(array.value(index)), precision, scale)
-        }
+    ) -> Result<ScalarValue> {
+        let array = match as_decimal128_array(array) {

Review Comment:
   Can you not do this with:
   ```rust
   let array = as_decimal128_array(array)?;
   if array.is_null(index) {
       Ok(ScalarValue::Decimal128(None, precision, scale))
   } else {
       let value = array.value(index);
       Ok(ScalarValue::Decimal128(Some(value), precision, scale))
   }
   ```



##########
datafusion/common/src/scalar.rs:
##########
@@ -2073,14 +2082,14 @@ impl ScalarValue {
         value: &Option<i128>,
         precision: u8,
         scale: u8,
-    ) -> bool {
-        let array = array.as_any().downcast_ref::<Decimal128Array>().unwrap();
+    ) -> Result<bool> {
+        let array = as_decimal128_array(array)?;
         if array.precision() != precision || array.scale() != scale {
-            return false;
+            return Ok(false);
         }
         match value {

Review Comment:
   Using `match` expressions with binary types like `Result` or `Option` is typically less idiomatic than using the `if let` expression. With this in mind, I suggest:
   ```rust
   let is_null = array.is_null(index);
   if let Some(v) = value {
     Ok(!is_null && array.value(index) == *v)
   } else {
     Ok(is_null)
   }
   ```



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