diff --git a/datafusion/functions-nested/src/cardinality.rs b/datafusion/functions-nested/src/cardinality.rs
index 6db0011cd078..58a83feb6676 100644
--- a/datafusion/functions-nested/src/cardinality.rs
+++ b/datafusion/functions-nested/src/cardinality.rs
@@ -117,8 +117,7 @@ impl ScalarUDFImpl for Cardinality {
     }
 }
 
-/// Cardinality SQL function
-pub fn cardinality_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn cardinality_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("cardinality", args)?;
     match array.data_type() {
         Null => Ok(Arc::new(UInt64Array::from_value(0, array.len()))),
diff --git a/datafusion/functions-nested/src/concat.rs b/datafusion/functions-nested/src/concat.rs
index 9a12db525f95..a565006a2577 100644
--- a/datafusion/functions-nested/src/concat.rs
+++ b/datafusion/functions-nested/src/concat.rs
@@ -352,8 +352,7 @@ impl ScalarUDFImpl for ArrayConcat {
     }
 }
 
-/// Array_concat/Array_cat SQL function
-pub(crate) fn array_concat_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_concat_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     if args.is_empty() {
         return exec_err!("array_concat expects at least one argument");
     }
@@ -453,8 +452,7 @@ fn concat_internal<O: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
 
 // Kernel functions
 
-/// Array_append SQL function
-pub(crate) fn array_append_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_append_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array, values] = take_function_args("array_append", args)?;
     match array.data_type() {
         DataType::Null => make_array_inner(&[Arc::clone(values)]),
@@ -464,8 +462,7 @@ pub(crate) fn array_append_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     }
 }
 
-/// Array_prepend SQL function
-pub(crate) fn array_prepend_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_prepend_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [values, array] = take_function_args("array_prepend", args)?;
     match array.data_type() {
         DataType::Null => make_array_inner(&[Arc::clone(values)]),
diff --git a/datafusion/functions-nested/src/dimension.rs b/datafusion/functions-nested/src/dimension.rs
index b0fc5bee5494..d0fa294fe42d 100644
--- a/datafusion/functions-nested/src/dimension.rs
+++ b/datafusion/functions-nested/src/dimension.rs
@@ -189,8 +189,7 @@ impl ScalarUDFImpl for ArrayNdims {
     }
 }
 
-/// Array_dims SQL function
-pub fn array_dims_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_dims_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("array_dims", args)?;
     let data: Vec<_> = match array.data_type() {
         List(_) => as_list_array(&array)?
@@ -214,8 +213,7 @@ pub fn array_dims_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     Ok(Arc::new(result))
 }
 
-/// Array_ndims SQL function
-pub fn array_ndims_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_ndims_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("array_ndims", args)?;
 
     fn general_list_ndims(array: &ArrayRef) -> Result<ArrayRef> {
diff --git a/datafusion/functions-nested/src/distance.rs b/datafusion/functions-nested/src/distance.rs
index e2e38fbd0d83..dc8eaa699f87 100644
--- a/datafusion/functions-nested/src/distance.rs
+++ b/datafusion/functions-nested/src/distance.rs
@@ -141,7 +141,7 @@ impl ScalarUDFImpl for ArrayDistance {
     }
 }
 
-pub fn array_distance_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_distance_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array1, array2] = take_function_args("array_distance", args)?;
     match (array1.data_type(), array2.data_type()) {
         (List(_), List(_)) => general_array_distance::<i32>(args),
diff --git a/datafusion/functions-nested/src/empty.rs b/datafusion/functions-nested/src/empty.rs
index 27a90ab0442b..3f9077575205 100644
--- a/datafusion/functions-nested/src/empty.rs
+++ b/datafusion/functions-nested/src/empty.rs
@@ -110,8 +110,7 @@ impl ScalarUDFImpl for ArrayEmpty {
     }
 }
 
-/// Array_empty SQL function
-pub fn array_empty_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_empty_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("array_empty", args)?;
     match array.data_type() {
         List(_) => general_array_empty::<i32>(array),
diff --git a/datafusion/functions-nested/src/except.rs b/datafusion/functions-nested/src/except.rs
index d6982ab5a2ab..8b6bcaa0620c 100644
--- a/datafusion/functions-nested/src/except.rs
+++ b/datafusion/functions-nested/src/except.rs
@@ -126,8 +126,7 @@ impl ScalarUDFImpl for ArrayExcept {
     }
 }
 
-/// Array_except SQL function
-pub fn array_except_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_except_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array1, array2] = take_function_args("array_except", args)?;
 
     match (array1.data_type(), array2.data_type()) {
diff --git a/datafusion/functions-nested/src/flatten.rs b/datafusion/functions-nested/src/flatten.rs
index e84a942fab2a..76c4714de1af 100644
--- a/datafusion/functions-nested/src/flatten.rs
+++ b/datafusion/functions-nested/src/flatten.rs
@@ -130,8 +130,7 @@ impl ScalarUDFImpl for Flatten {
     }
 }
 
-/// Flatten SQL function
-pub fn flatten_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn flatten_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("flatten", args)?;
 
     match array.data_type() {
diff --git a/datafusion/functions-nested/src/length.rs b/datafusion/functions-nested/src/length.rs
index 060a978185e5..ceceee7bfa52 100644
--- a/datafusion/functions-nested/src/length.rs
+++ b/datafusion/functions-nested/src/length.rs
@@ -150,8 +150,7 @@ macro_rules! array_length_impl {
     }};
 }
 
-/// Array_length SQL function
-pub fn array_length_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_length_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     if args.len() != 1 && args.len() != 2 {
         return exec_err!("array_length expects one or two arguments");
     }
diff --git a/datafusion/functions-nested/src/min_max.rs b/datafusion/functions-nested/src/min_max.rs
index 117cfbeaa2b2..1f3623ca243d 100644
--- a/datafusion/functions-nested/src/min_max.rs
+++ b/datafusion/functions-nested/src/min_max.rs
@@ -113,14 +113,7 @@ impl ScalarUDFImpl for ArrayMax {
     }
 }
 
-/// array_max SQL function
-///
-/// There is one argument for array_max as the array.
-/// `array_max(array)`
-///
-/// For example:
-/// > array_max(\[1, 3, 2]) -> 3
-pub fn array_max_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_max_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("array_max", args)?;
     match array.data_type() {
         List(_) => array_min_max_helper(as_list_array(array)?, max_batch),
@@ -202,7 +195,7 @@ impl ScalarUDFImpl for ArrayMin {
     }
 }
 
-pub fn array_min_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_min_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("array_min", args)?;
     match array.data_type() {
         List(_) => array_min_max_helper(as_list_array(array)?, min_batch),
diff --git a/datafusion/functions-nested/src/position.rs b/datafusion/functions-nested/src/position.rs
index b390bf3c4226..14f2ed3313d4 100644
--- a/datafusion/functions-nested/src/position.rs
+++ b/datafusion/functions-nested/src/position.rs
@@ -141,8 +141,7 @@ impl ScalarUDFImpl for ArrayPosition {
     }
 }
 
-/// Array_position SQL function
-pub fn array_position_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_position_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     if args.len() < 2 || args.len() > 3 {
         return exec_err!("array_position expects two or three arguments");
     }
@@ -152,6 +151,7 @@ pub fn array_position_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
         array_type => exec_err!("array_position does not support type '{array_type}'."),
     }
 }
+
 fn general_position_dispatch<O: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
     let list_array = as_generic_list_array::<O>(&args[0])?;
     let element_array = &args[1];
@@ -292,8 +292,7 @@ impl ScalarUDFImpl for ArrayPositions {
     }
 }
 
-/// Array_positions SQL function
-pub fn array_positions_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_positions_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array, element] = take_function_args("array_positions", args)?;
 
     match &array.data_type() {
diff --git a/datafusion/functions-nested/src/remove.rs b/datafusion/functions-nested/src/remove.rs
index e1ebc9cda0bf..46111b0c2d12 100644
--- a/datafusion/functions-nested/src/remove.rs
+++ b/datafusion/functions-nested/src/remove.rs
@@ -284,24 +284,21 @@ impl ScalarUDFImpl for ArrayRemoveAll {
     }
 }
 
-/// Array_remove SQL function
-pub fn array_remove_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_remove_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array, element] = take_function_args("array_remove", args)?;
 
     let arr_n = vec![1; array.len()];
     array_remove_internal(array, element, &arr_n)
 }
 
-/// Array_remove_n SQL function
-pub fn array_remove_n_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_remove_n_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array, element, max] = take_function_args("array_remove_n", args)?;
 
     let arr_n = as_int64_array(max)?.values().to_vec();
     array_remove_internal(array, element, &arr_n)
 }
 
-/// Array_remove_all SQL function
-pub fn array_remove_all_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_remove_all_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array, element] = take_function_args("array_remove_all", args)?;
 
     let arr_n = vec![i64::MAX; array.len()];
diff --git a/datafusion/functions-nested/src/repeat.rs b/datafusion/functions-nested/src/repeat.rs
index ed66b9e39676..d978081e490c 100644
--- a/datafusion/functions-nested/src/repeat.rs
+++ b/datafusion/functions-nested/src/repeat.rs
@@ -148,8 +148,7 @@ impl ScalarUDFImpl for ArrayRepeat {
     }
 }
 
-/// Array_repeat SQL function
-pub fn array_repeat_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_repeat_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let element = &args[0];
     let count_array = &args[1];
 
diff --git a/datafusion/functions-nested/src/replace.rs b/datafusion/functions-nested/src/replace.rs
index 079c28175d45..53182b58988f 100644
--- a/datafusion/functions-nested/src/replace.rs
+++ b/datafusion/functions-nested/src/replace.rs
@@ -418,7 +418,7 @@ fn general_replace<O: OffsetSizeTrait>(
     )?))
 }
 
-pub(crate) fn array_replace_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_replace_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array, from, to] = take_function_args("array_replace", args)?;
 
     // replace at most one occurrence for each element
@@ -437,7 +437,7 @@ pub(crate) fn array_replace_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     }
 }
 
-pub(crate) fn array_replace_n_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_replace_n_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array, from, to, max] = take_function_args("array_replace_n", args)?;
 
     // replace the specified number of occurrences
@@ -458,7 +458,7 @@ pub(crate) fn array_replace_n_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     }
 }
 
-pub(crate) fn array_replace_all_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_replace_all_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array, from, to] = take_function_args("array_replace_all", args)?;
 
     // replace all occurrences (up to "i64::MAX")
diff --git a/datafusion/functions-nested/src/resize.rs b/datafusion/functions-nested/src/resize.rs
index 09f67a75fd56..c76f7970d206 100644
--- a/datafusion/functions-nested/src/resize.rs
+++ b/datafusion/functions-nested/src/resize.rs
@@ -152,8 +152,7 @@ impl ScalarUDFImpl for ArrayResize {
     }
 }
 
-/// array_resize SQL function
-pub(crate) fn array_resize_inner(arg: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_resize_inner(arg: &[ArrayRef]) -> Result<ArrayRef> {
     if arg.len() < 2 || arg.len() > 3 {
         return exec_err!("array_resize needs two or three arguments");
     }
diff --git a/datafusion/functions-nested/src/set_ops.rs b/datafusion/functions-nested/src/set_ops.rs
index 71a42531f99e..e3531d1cf8ee 100644
--- a/datafusion/functions-nested/src/set_ops.rs
+++ b/datafusion/functions-nested/src/set_ops.rs
@@ -501,13 +501,11 @@ fn general_set_op(
     }
 }
 
-/// Array_union SQL function
 fn array_union_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array1, array2] = take_function_args("array_union", args)?;
     general_set_op(array1, array2, SetOp::Union)
 }
 
-/// array_intersect SQL function
 fn array_intersect_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array1, array2] = take_function_args("array_intersect", args)?;
     general_set_op(array1, array2, SetOp::Intersect)
diff --git a/datafusion/functions-nested/src/sort.rs b/datafusion/functions-nested/src/sort.rs
index 4a7aa31c755b..8cfc8a297b7b 100644
--- a/datafusion/functions-nested/src/sort.rs
+++ b/datafusion/functions-nested/src/sort.rs
@@ -164,8 +164,7 @@ impl ScalarUDFImpl for ArraySort {
     }
 }
 
-/// Array_sort SQL function
-pub fn array_sort_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_sort_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     if args.is_empty() || args.len() > 3 {
         return exec_err!("array_sort expects one to three arguments");
     }
@@ -218,8 +217,7 @@ pub fn array_sort_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     }
 }
 
-/// Array_sort SQL function
-pub fn array_sort_generic<OffsetSize: OffsetSizeTrait>(
+fn array_sort_generic<OffsetSize: OffsetSizeTrait>(
     list_array: &GenericListArray<OffsetSize>,
     field: &FieldRef,
     sort_options: Option<SortOptions>,
diff --git a/datafusion/functions-nested/src/string.rs b/datafusion/functions-nested/src/string.rs
index b87ac0f8c41d..e19025cf673e 100644
--- a/datafusion/functions-nested/src/string.rs
+++ b/datafusion/functions-nested/src/string.rs
@@ -329,8 +329,7 @@ impl ScalarUDFImpl for StringToArray {
     }
 }
 
-/// Array_to_string SQL function
-pub(super) fn array_to_string_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_to_string_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     if args.len() < 2 || args.len() > 3 {
         return exec_err!("array_to_string expects two or three arguments");
     }
diff --git a/datafusion/functions/src/core/overlay.rs b/datafusion/functions/src/core/overlay.rs
index 165bc571afe0..0b3bb2ce7413 100644
--- a/datafusion/functions/src/core/overlay.rs
+++ b/datafusion/functions/src/core/overlay.rs
@@ -201,7 +201,7 @@ fn overlay<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
     }
 }
 
-pub fn string_overlay<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn string_overlay<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
     match args.len() {
         3 => {
             let string_array = as_generic_string_array::<T>(&args[0])?;
@@ -227,7 +227,7 @@ pub fn string_overlay<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef>
     }
 }
 
-pub fn string_view_overlay<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn string_view_overlay<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
     match args.len() {
         3 => {
             let string_array = as_string_view_array(&args[0])?;
diff --git a/datafusion/functions/src/core/version.rs b/datafusion/functions/src/core/version.rs
index ef3c5aafa480..006da4b132ad 100644
--- a/datafusion/functions/src/core/version.rs
+++ b/datafusion/functions/src/core/version.rs
@@ -53,7 +53,7 @@ impl Default for VersionFunc {
 impl VersionFunc {
     pub fn new() -> Self {
         Self {
-            signature: Signature::exact(vec![], Volatility::Immutable),
+            signature: Signature::nullary(Volatility::Immutable),
         }
     }
 }
diff --git a/datafusion/functions/src/math/iszero.rs b/datafusion/functions/src/math/iszero.rs
index 68cd3aca28fd..f053256a4870 100644
--- a/datafusion/functions/src/math/iszero.rs
+++ b/datafusion/functions/src/math/iszero.rs
@@ -96,7 +96,7 @@ impl ScalarUDFImpl for IsZeroFunc {
 }
 
 /// Iszero SQL function
-pub fn iszero(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn iszero(args: &[ArrayRef]) -> Result<ArrayRef> {
     match args[0].data_type() {
         Float64 => Ok(Arc::new(BooleanArray::from_unary(
             args[0].as_primitive::<Float64Type>(),
diff --git a/datafusion/functions/src/math/round.rs b/datafusion/functions/src/math/round.rs
index 837f0be43240..5f9b1eb6ad58 100644
--- a/datafusion/functions/src/math/round.rs
+++ b/datafusion/functions/src/math/round.rs
@@ -124,7 +124,7 @@ impl ScalarUDFImpl for RoundFunc {
 }
 
 /// Round SQL function
-pub fn round(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn round(args: &[ArrayRef]) -> Result<ArrayRef> {
     if args.len() != 1 && args.len() != 2 {
         return exec_err!(
             "round function requires one or two arguments, got {}",
diff --git a/datafusion/functions/src/math/signum.rs b/datafusion/functions/src/math/signum.rs
index bbe6178f39b7..2e616fe0fe35 100644
--- a/datafusion/functions/src/math/signum.rs
+++ b/datafusion/functions/src/math/signum.rs
@@ -107,7 +107,7 @@ impl ScalarUDFImpl for SignumFunc {
 }
 
 /// signum SQL function
-pub fn signum(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn signum(args: &[ArrayRef]) -> Result<ArrayRef> {
     match args[0].data_type() {
         Float64 => Ok(Arc::new(
             args[0]
diff --git a/datafusion/functions/src/regex/regexpcount.rs b/datafusion/functions/src/regex/regexpcount.rs
index e61b3f764dc6..ae08ca3e920c 100644
--- a/datafusion/functions/src/regex/regexpcount.rs
+++ b/datafusion/functions/src/regex/regexpcount.rs
@@ -183,7 +183,7 @@ pub fn regexp_count_func(args: &[ArrayRef]) -> Result<ArrayRef> {
 ///
 /// # Errors
 /// Returns an error if the input arrays have mismatched lengths or if the regular expression fails to compile.
-pub fn regexp_count(
+fn regexp_count(
     values: &dyn Array,
     regex_array: &dyn Datum,
     start_array: Option<&dyn Datum>,
diff --git a/datafusion/functions/src/regex/regexpinstr.rs b/datafusion/functions/src/regex/regexpinstr.rs
index 10fddda1a35b..011564866584 100644
--- a/datafusion/functions/src/regex/regexpinstr.rs
+++ b/datafusion/functions/src/regex/regexpinstr.rs
@@ -205,7 +205,7 @@ pub fn regexp_instr_func(args: &[ArrayRef]) -> Result<ArrayRef> {
 ///
 /// # Errors
 /// Returns an error if the input arrays have mismatched lengths or if the regular expression fails to compile.
-pub fn regexp_instr(
+fn regexp_instr(
     values: &dyn Array,
     regex_array: &dyn Datum,
     start_array: Option<&dyn Datum>,
@@ -233,48 +233,48 @@ pub fn regexp_instr(
 
     match (values.data_type(), regex_array.data_type(), flags_array) {
         (Utf8, Utf8, None) => regexp_instr_inner(
-            values.as_string::<i32>(),
-            regex_array.as_string::<i32>(),
+            &values.as_string::<i32>(),
+            &regex_array.as_string::<i32>(),
             start_array.map(|start| start.as_primitive::<Int64Type>()),
             nth_array.map(|nth| nth.as_primitive::<Int64Type>()),
             None,
             subexpr_array.map(|subexpr| subexpr.as_primitive::<Int64Type>()),
         ),
         (Utf8, Utf8, Some(flags_array)) if *flags_array.data_type() == Utf8 => regexp_instr_inner(
-            values.as_string::<i32>(),
-            regex_array.as_string::<i32>(),
+            &values.as_string::<i32>(),
+            &regex_array.as_string::<i32>(),
             start_array.map(|start| start.as_primitive::<Int64Type>()),
             nth_array.map(|nth| nth.as_primitive::<Int64Type>()),
             Some(flags_array.as_string::<i32>()),
             subexpr_array.map(|subexpr| subexpr.as_primitive::<Int64Type>()),
         ),
         (LargeUtf8, LargeUtf8, None) => regexp_instr_inner(
-            values.as_string::<i64>(),
-            regex_array.as_string::<i64>(),
+            &values.as_string::<i64>(),
+            &regex_array.as_string::<i64>(),
             start_array.map(|start| start.as_primitive::<Int64Type>()),
             nth_array.map(|nth| nth.as_primitive::<Int64Type>()),
             None,
             subexpr_array.map(|subexpr| subexpr.as_primitive::<Int64Type>()),
         ),
         (LargeUtf8, LargeUtf8, Some(flags_array)) if *flags_array.data_type() == LargeUtf8 => regexp_instr_inner(
-            values.as_string::<i64>(),
-            regex_array.as_string::<i64>(),
+            &values.as_string::<i64>(),
+            &regex_array.as_string::<i64>(),
             start_array.map(|start| start.as_primitive::<Int64Type>()),
             nth_array.map(|nth| nth.as_primitive::<Int64Type>()),
             Some(flags_array.as_string::<i64>()),
             subexpr_array.map(|subexpr| subexpr.as_primitive::<Int64Type>()),
         ),
         (Utf8View, Utf8View, None) => regexp_instr_inner(
-            values.as_string_view(),
-            regex_array.as_string_view(),
+            &values.as_string_view(),
+            &regex_array.as_string_view(),
             start_array.map(|start| start.as_primitive::<Int64Type>()),
             nth_array.map(|nth| nth.as_primitive::<Int64Type>()),
             None,
             subexpr_array.map(|subexpr| subexpr.as_primitive::<Int64Type>()),
         ),
         (Utf8View, Utf8View, Some(flags_array)) if *flags_array.data_type() == Utf8View => regexp_instr_inner(
-            values.as_string_view(),
-            regex_array.as_string_view(),
+            &values.as_string_view(),
+            &regex_array.as_string_view(),
             start_array.map(|start| start.as_primitive::<Int64Type>()),
             nth_array.map(|nth| nth.as_primitive::<Int64Type>()),
             Some(flags_array.as_string_view()),
@@ -287,10 +287,9 @@ pub fn regexp_instr(
 }
 
 #[allow(clippy::too_many_arguments)]
-#[expect(clippy::needless_pass_by_value)]
-pub fn regexp_instr_inner<'a, S>(
-    values: S,
-    regex_array: S,
+fn regexp_instr_inner<'a, S>(
+    values: &S,
+    regex_array: &S,
     start_array: Option<&Int64Array>,
     nth_array: Option<&Int64Array>,
     flags_array: Option<S>,
diff --git a/datafusion/functions/src/regex/regexpreplace.rs b/datafusion/functions/src/regex/regexpreplace.rs
index f9866427139f..29da195c7a92 100644
--- a/datafusion/functions/src/regex/regexpreplace.rs
+++ b/datafusion/functions/src/regex/regexpreplace.rs
@@ -76,7 +76,7 @@ Additional examples can be found [here](https://github.com/apache/datafusion/blo
     argument(
         name = "flags",
         description = r#"Optional regular expression flags that control the behavior of the regular expression. The following flags are supported:
-- **g**: (global) Search globally and don't return after the first match        
+- **g**: (global) Search globally and don't return after the first match
 - **i**: case-insensitive: letters match both upper and lower case
 - **m**: multi-line mode: ^ and $ match begin/end of line
 - **s**: allow . to match \n
@@ -382,49 +382,32 @@ where
     }
 }
 
-#[expect(clippy::needless_pass_by_value)]
-fn _regexp_replace_early_abort<T: ArrayAccessor>(
-    input_array: T,
-    sz: usize,
-) -> Result<ArrayRef> {
-    // Mimicking the existing behavior of regexp_replace, if any of the scalar arguments
-    // are actually null, then the result will be an array of the same size as the first argument with all nulls.
-    //
-    // Also acts like an early abort mechanism when the input array is empty.
-    Ok(new_null_array(input_array.data_type(), sz))
-}
-
 /// Get the first argument from the given string array.
 ///
 /// Note: If the array is empty or the first argument is null,
-/// then calls the given early abort function.
+/// then aborts early.
 macro_rules! fetch_string_arg {
-    ($ARG:expr, $NAME:expr, $EARLY_ABORT:ident, $ARRAY_SIZE:expr) => {{
+    ($ARG:expr, $NAME:expr, $ARRAY_SIZE:expr) => {{
         let string_array_type = ($ARG).data_type();
         match string_array_type {
+            dt if $ARG.len() == 0 || $ARG.is_null(0) => {
+                // Mimicking the existing behavior of regexp_replace, if any of the scalar arguments
+                // are actually null, then the result will be an array of the same size as the first argument with all nulls.
+                //
+                // Also acts like an early abort mechanism when the input array is empty.
+                return Ok(new_null_array(dt, $ARRAY_SIZE));
+            }
             DataType::Utf8 => {
                 let array = as_string_array($ARG)?;
-                if array.len() == 0 || array.is_null(0) {
-                    return $EARLY_ABORT(array, $ARRAY_SIZE);
-                } else {
-                    array.value(0)
-                }
+                array.value(0)
             }
             DataType::LargeUtf8 => {
                 let array = as_large_string_array($ARG)?;
-                if array.len() == 0 || array.is_null(0) {
-                    return $EARLY_ABORT(array, $ARRAY_SIZE);
-                } else {
-                    array.value(0)
-                }
+                array.value(0)
             }
             DataType::Utf8View => {
                 let array = as_string_view_array($ARG)?;
-                if array.len() == 0 || array.is_null(0) {
-                    return $EARLY_ABORT(array, $ARRAY_SIZE);
-                } else {
-                    array.value(0)
-                }
+                array.value(0)
             }
             _ => unreachable!(
                 "Invalid data type for regexp_replace: {}",
@@ -443,17 +426,11 @@ fn _regexp_replace_static_pattern_replace<T: OffsetSizeTrait>(
     args: &[ArrayRef],
 ) -> Result<ArrayRef> {
     let array_size = args[0].len();
-    let pattern =
-        fetch_string_arg!(&args[1], "pattern", _regexp_replace_early_abort, array_size);
-    let replacement = fetch_string_arg!(
-        &args[2],
-        "replacement",
-        _regexp_replace_early_abort,
-        array_size
-    );
+    let pattern = fetch_string_arg!(&args[1], "pattern", array_size);
+    let replacement = fetch_string_arg!(&args[2], "replacement", array_size);
     let flags = match args.len() {
         3 => None,
-        4 => Some(fetch_string_arg!(&args[3], "flags", _regexp_replace_early_abort, array_size)),
+        4 => Some(fetch_string_arg!(&args[3], "flags", array_size)),
         other => {
             return exec_err!(
                 "regexp_replace was called with {other} arguments. It requires at least 3 and at most 4."
@@ -538,7 +515,7 @@ fn _regexp_replace_static_pattern_replace<T: OffsetSizeTrait>(
 
 /// Determine which implementation of the regexp_replace to use based
 /// on the given set of arguments.
-pub fn specialize_regexp_replace<T: OffsetSizeTrait>(
+fn specialize_regexp_replace<T: OffsetSizeTrait>(
     args: &[ColumnarValue],
 ) -> Result<ArrayRef> {
     // This will serve as a dispatch table where we can
diff --git a/datafusion/functions/src/string/chr.rs b/datafusion/functions/src/string/chr.rs
index 4d2beafbae53..8706c43214ea 100644
--- a/datafusion/functions/src/string/chr.rs
+++ b/datafusion/functions/src/string/chr.rs
@@ -33,7 +33,7 @@ use datafusion_macros::user_doc;
 
 /// Returns the character with the given code.
 /// chr(65) = 'A'
-pub fn chr(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn chr(args: &[ArrayRef]) -> Result<ArrayRef> {
     let integer_array = as_int64_array(&args[0])?;
 
     let mut builder = GenericStringBuilder::<i32>::with_capacity(
diff --git a/datafusion/functions/src/string/common.rs b/datafusion/functions/src/string/common.rs
index 6bce289edb4c..34f1b6232d41 100644
--- a/datafusion/functions/src/string/common.rs
+++ b/datafusion/functions/src/string/common.rs
@@ -32,6 +32,7 @@ use datafusion_common::Result;
 use datafusion_common::{exec_err, ScalarValue};
 use datafusion_expr::ColumnarValue;
 
+#[derive(Copy, Clone)]
 pub(crate) enum TrimType {
     Left,
     Right,
@@ -48,7 +49,6 @@ impl Display for TrimType {
     }
 }
 
-#[expect(clippy::needless_pass_by_value)]
 pub(crate) fn general_trim<T: OffsetSizeTrait>(
     args: &[ArrayRef],
     trim_type: TrimType,
diff --git a/datafusion/functions/src/string/concat.rs b/datafusion/functions/src/string/concat.rs
index a93e70e714e8..3b53660463d4 100644
--- a/datafusion/functions/src/string/concat.rs
+++ b/datafusion/functions/src/string/concat.rs
@@ -287,7 +287,7 @@ impl ScalarUDFImpl for ConcatFunc {
     }
 }
 
-pub fn simplify_concat(args: Vec<Expr>) -> Result<ExprSimplifyResult> {
+pub(crate) fn simplify_concat(args: Vec<Expr>) -> Result<ExprSimplifyResult> {
     let mut new_args = Vec::with_capacity(args.len());
     let mut contiguous_scalar = "".to_string();
 
diff --git a/datafusion/functions/src/string/split_part.rs b/datafusion/functions/src/string/split_part.rs
index b32eba990d76..c8b293f29811 100644
--- a/datafusion/functions/src/string/split_part.rs
+++ b/datafusion/functions/src/string/split_part.rs
@@ -123,64 +123,64 @@ impl ScalarUDFImpl for SplitPartFunc {
         let result = match (args[0].data_type(), args[1].data_type()) {
             (DataType::Utf8View, DataType::Utf8View) => {
                 split_part_impl::<&StringViewArray, &StringViewArray, i32>(
-                    args[0].as_string_view(),
-                    args[1].as_string_view(),
+                    &args[0].as_string_view(),
+                    &args[1].as_string_view(),
                     n_array,
                 )
             }
             (DataType::Utf8View, DataType::Utf8) => {
                 split_part_impl::<&StringViewArray, &GenericStringArray<i32>, i32>(
-                    args[0].as_string_view(),
-                    args[1].as_string::<i32>(),
+                    &args[0].as_string_view(),
+                    &args[1].as_string::<i32>(),
                     n_array,
                 )
             }
             (DataType::Utf8View, DataType::LargeUtf8) => {
                 split_part_impl::<&StringViewArray, &GenericStringArray<i64>, i32>(
-                    args[0].as_string_view(),
-                    args[1].as_string::<i64>(),
+                    &args[0].as_string_view(),
+                    &args[1].as_string::<i64>(),
                     n_array,
                 )
             }
             (DataType::Utf8, DataType::Utf8View) => {
                 split_part_impl::<&GenericStringArray<i32>, &StringViewArray, i32>(
-                    args[0].as_string::<i32>(),
-                    args[1].as_string_view(),
+                    &args[0].as_string::<i32>(),
+                    &args[1].as_string_view(),
                     n_array,
                 )
             }
             (DataType::LargeUtf8, DataType::Utf8View) => {
                 split_part_impl::<&GenericStringArray<i64>, &StringViewArray, i64>(
-                    args[0].as_string::<i64>(),
-                    args[1].as_string_view(),
+                    &args[0].as_string::<i64>(),
+                    &args[1].as_string_view(),
                     n_array,
                 )
             }
             (DataType::Utf8, DataType::Utf8) => {
                 split_part_impl::<&GenericStringArray<i32>, &GenericStringArray<i32>, i32>(
-                    args[0].as_string::<i32>(),
-                    args[1].as_string::<i32>(),
+                    &args[0].as_string::<i32>(),
+                    &args[1].as_string::<i32>(),
                     n_array,
                 )
             }
             (DataType::LargeUtf8, DataType::LargeUtf8) => {
                 split_part_impl::<&GenericStringArray<i64>, &GenericStringArray<i64>, i64>(
-                    args[0].as_string::<i64>(),
-                    args[1].as_string::<i64>(),
+                    &args[0].as_string::<i64>(),
+                    &args[1].as_string::<i64>(),
                     n_array,
                 )
             }
             (DataType::Utf8, DataType::LargeUtf8) => {
                 split_part_impl::<&GenericStringArray<i32>, &GenericStringArray<i64>, i32>(
-                    args[0].as_string::<i32>(),
-                    args[1].as_string::<i64>(),
+                    &args[0].as_string::<i32>(),
+                    &args[1].as_string::<i64>(),
                     n_array,
                 )
             }
             (DataType::LargeUtf8, DataType::Utf8) => {
                 split_part_impl::<&GenericStringArray<i64>, &GenericStringArray<i32>, i64>(
-                    args[0].as_string::<i64>(),
-                    args[1].as_string::<i32>(),
+                    &args[0].as_string::<i64>(),
+                    &args[1].as_string::<i32>(),
                     n_array,
                 )
             }
@@ -200,11 +200,9 @@ impl ScalarUDFImpl for SplitPartFunc {
     }
 }
 
-/// impl
-#[expect(clippy::needless_pass_by_value)]
-pub fn split_part_impl<'a, StringArrType, DelimiterArrType, StringArrayLen>(
-    string_array: StringArrType,
-    delimiter_array: DelimiterArrType,
+fn split_part_impl<'a, StringArrType, DelimiterArrType, StringArrayLen>(
+    string_array: &StringArrType,
+    delimiter_array: &DelimiterArrType,
     n_array: &Int64Array,
 ) -> Result<ArrayRef>
 where
diff --git a/datafusion/functions/src/string/to_hex.rs b/datafusion/functions/src/string/to_hex.rs
index 26be0066c2df..4000f3bb3be2 100644
--- a/datafusion/functions/src/string/to_hex.rs
+++ b/datafusion/functions/src/string/to_hex.rs
@@ -39,7 +39,7 @@ use datafusion_macros::user_doc;
 
 /// Converts the number to its equivalent hexadecimal representation.
 /// to_hex(2147483647) = '7fffffff'
-pub fn to_hex<T: ArrowPrimitiveType>(args: &[ArrayRef]) -> Result<ArrayRef>
+fn to_hex<T: ArrowPrimitiveType>(args: &[ArrayRef]) -> Result<ArrayRef>
 where
     T::Native: std::fmt::LowerHex,
 {
diff --git a/datafusion/functions/src/unicode/find_in_set.rs b/datafusion/functions/src/unicode/find_in_set.rs
index 649bd631d142..e83e3d99a329 100644
--- a/datafusion/functions/src/unicode/find_in_set.rs
+++ b/datafusion/functions/src/unicode/find_in_set.rs
@@ -263,10 +263,7 @@ fn find_in_set(str: &ArrayRef, str_list: &ArrayRef) -> Result<ArrayRef> {
     }
 }
 
-pub fn find_in_set_general<'a, T, V>(
-    string_array: V,
-    str_list_array: V,
-) -> Result<ArrayRef>
+fn find_in_set_general<'a, T, V>(string_array: V, str_list_array: V) -> Result<ArrayRef>
 where
     T: ArrowPrimitiveType,
     T::Native: OffsetSizeTrait,
diff --git a/datafusion/functions/src/unicode/left.rs b/datafusion/functions/src/unicode/left.rs
index fceb2a131a2b..ec7ec456ab8b 100644
--- a/datafusion/functions/src/unicode/left.rs
+++ b/datafusion/functions/src/unicode/left.rs
@@ -122,7 +122,7 @@ impl ScalarUDFImpl for LeftFunc {
 /// Returns first n characters in the string, or when n is negative, returns all but last |n| characters.
 /// left('abcde', 2) = 'ab'
 /// The implementation uses UTF-8 code points as characters
-pub fn left<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn left<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
     let n_array = as_int64_array(&args[1])?;
 
     if args[0].data_type() == &DataType::Utf8View {
diff --git a/datafusion/functions/src/unicode/lpad.rs b/datafusion/functions/src/unicode/lpad.rs
index b69af247b9ad..6940459b177a 100644
--- a/datafusion/functions/src/unicode/lpad.rs
+++ b/datafusion/functions/src/unicode/lpad.rs
@@ -129,7 +129,7 @@ impl ScalarUDFImpl for LPadFunc {
 /// Extends the string to length 'length' by prepending the characters fill (a space by default).
 /// If the string is already longer than length then it is truncated (on the right).
 /// lpad('hi', 5, 'xy') = 'xyxhi'
-pub fn lpad<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn lpad<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
     if args.len() <= 1 || args.len() > 3 {
         return exec_err!(
             "lpad was called with {} arguments. It requires at least 2 and at most 3.",
diff --git a/datafusion/functions/src/unicode/reverse.rs b/datafusion/functions/src/unicode/reverse.rs
index b5f870d54bba..56f6048d6b6e 100644
--- a/datafusion/functions/src/unicode/reverse.rs
+++ b/datafusion/functions/src/unicode/reverse.rs
@@ -106,7 +106,7 @@ impl ScalarUDFImpl for ReverseFunc {
 
 /// Reverses the order of the characters in the string `reverse('abcde') = 'edcba'`.
 /// The implementation uses UTF-8 code points as characters
-pub fn reverse<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn reverse<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
     if args[0].data_type() == &Utf8View {
         reverse_impl::<T, _>(&args[0].as_string_view())
     } else {
diff --git a/datafusion/functions/src/unicode/right.rs b/datafusion/functions/src/unicode/right.rs
index c492f606e9c5..670586e11b4f 100644
--- a/datafusion/functions/src/unicode/right.rs
+++ b/datafusion/functions/src/unicode/right.rs
@@ -122,7 +122,7 @@ impl ScalarUDFImpl for RightFunc {
 /// Returns last n characters in the string, or when n is negative, returns all but first |n| characters.
 /// right('abcde', 2) = 'de'
 /// The implementation uses UTF-8 code points as characters
-pub fn right<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn right<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
     let n_array = as_int64_array(&args[1])?;
     if args[0].data_type() == &DataType::Utf8View {
         // string_view_right(args)
diff --git a/datafusion/functions/src/unicode/rpad.rs b/datafusion/functions/src/unicode/rpad.rs
index d644df9874eb..a7e951051d7c 100644
--- a/datafusion/functions/src/unicode/rpad.rs
+++ b/datafusion/functions/src/unicode/rpad.rs
@@ -145,7 +145,7 @@ impl ScalarUDFImpl for RPadFunc {
     }
 }
 
-pub fn rpad<StringArrayLen: OffsetSizeTrait, FillArrayLen: OffsetSizeTrait>(
+fn rpad<StringArrayLen: OffsetSizeTrait, FillArrayLen: OffsetSizeTrait>(
     args: &[ArrayRef],
 ) -> Result<ArrayRef> {
     if args.len() < 2 || args.len() > 3 {
@@ -205,7 +205,7 @@ pub fn rpad<StringArrayLen: OffsetSizeTrait, FillArrayLen: OffsetSizeTrait>(
 
 /// Extends the string to length 'length' by appending the characters fill (a space by default). If the string is already longer than length then it is truncated.
 /// rpad('hi', 5, 'xy') = 'hixyx'
-pub fn rpad_impl<'a, StringArrType, FillArrType, StringArrayLen>(
+fn rpad_impl<'a, StringArrType, FillArrType, StringArrayLen>(
     string_array: &StringArrType,
     length_array: &Int64Array,
     fill_array: Option<FillArrType>,
diff --git a/datafusion/functions/src/unicode/substr.rs b/datafusion/functions/src/unicode/substr.rs
index 6eee49d49093..27b194ca2b99 100644
--- a/datafusion/functions/src/unicode/substr.rs
+++ b/datafusion/functions/src/unicode/substr.rs
@@ -141,7 +141,7 @@ impl ScalarUDFImpl for SubstrFunc {
 /// substr('alphabet', 3) = 'phabet'
 /// substr('alphabet', 3, 2) = 'ph'
 /// The implementation uses UTF-8 code points as characters
-pub fn substr(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn substr(args: &[ArrayRef]) -> Result<ArrayRef> {
     match args[0].data_type() {
         DataType::Utf8 => {
             let string_array = args[0].as_string::<i32>();
diff --git a/datafusion/functions/src/unicode/substrindex.rs b/datafusion/functions/src/unicode/substrindex.rs
index a7ee7388f901..bf5978720692 100644
--- a/datafusion/functions/src/unicode/substrindex.rs
+++ b/datafusion/functions/src/unicode/substrindex.rs
@@ -169,7 +169,7 @@ fn substr_index(args: &[ArrayRef]) -> Result<ArrayRef> {
     }
 }
 
-pub fn substr_index_general<
+fn substr_index_general<
     'a,
     T: ArrowPrimitiveType,
     V: ArrayAccessor<Item = &'a str>,