add comments

arrow-cast/src/cast/dictionary.rs

@@ -189,24 +189,28 @@ pub(crate) fn cast_to_dictionary<K: ArrowDictionaryKeyType>(
  pack_numeric_to_dictionary::<K, Decimal256Type>(array, dict_value_type, cast_options)
  }
  Utf8 => {
+ // If the input is a view type, we can avoid casting (thus copying) the data
  if array.data_type() == &DataType::Utf8View {
  return string_view_to_dictionary::<K, i32>(array);
  }
  pack_byte_to_dictionary::<K, GenericStringType<i32>>(array, cast_options)
  }
  LargeUtf8 => {
+ // If the input is a view type, we can avoid casting (thus copying) the data
  if array.data_type() == &DataType::Utf8View {
  return string_view_to_dictionary::<K, i64>(array);
  }
  pack_byte_to_dictionary::<K, GenericStringType<i64>>(array, cast_options)
  }
  Binary => {
+ // If the input is a view type, we can avoid casting (thus copying) the data
  if array.data_type() == &DataType::BinaryView {
  return binary_view_to_dictionary::<K, i32>(array);
  }
  pack_byte_to_dictionary::<K, GenericBinaryType<i32>>(array, cast_options)
  }
  LargeBinary => {
+ // If the input is a view type, we can avoid casting (thus copying) the data
  if array.data_type() == &DataType::BinaryView {
  return binary_view_to_dictionary::<K, i64>(array);
  }
@@ -269,7 +273,7 @@ where
  }
  }
 
- return Ok(Arc::new(b.finish()));
+ Ok(Arc::new(b.finish()))
 }
 
 pub(crate) fn binary_view_to_dictionary<K, O: OffsetSizeTrait>(
@@ -295,7 +299,7 @@ where
  }
  }
 
- return Ok(Arc::new(b.finish()));
+ Ok(Arc::new(b.finish()))
 }
 
 // Packs the data as a GenericByteDictionaryBuilder, if possible, with the