2010YOUY01 commented on code in PR #14025:
URL: https://github.com/apache/datafusion/pull/14025#discussion_r1904948133


##########
datafusion/functions/src/unicode/reverse.rs:
##########
@@ -116,14 +115,23 @@ pub fn reverse<T: OffsetSizeTrait>(args: &[ArrayRef]) -> 
Result<ArrayRef> {
     }
 }
 
-fn reverse_impl<'a, T: OffsetSizeTrait, V: ArrayAccessor<Item = &'a str>>(
+fn reverse_impl<'a, T: OffsetSizeTrait, V: StringArrayType<'a>>(
     string_array: V,
 ) -> Result<ArrayRef> {
-    let result = ArrayIter::new(string_array)
-        .map(|string| string.map(|string: &str| 
string.chars().rev().collect::<String>()))
-        .collect::<GenericStringArray<T>>();
+    let mut builder: GenericStringBuilder<T> =
+        GenericStringBuilder::with_capacity(string_array.len(), 1024);

Review Comment:
   I think we can use the actual data size here for pre-allocation, instead of 
a constant 1024, the complexity of adding another argument for array size seems 
reasonable



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