[GitHub] [arrow] lidavidm commented on a change in pull request #10712: ARROW-13307: [C++][Python][R] Use reflection-based enums for function options

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

lidavidm commented on a change in pull request #10712:
URL: https://github.com/apache/arrow/pull/10712#discussion_r674112394



##########
File path: cpp/src/arrow/compute/function_internal.h
##########
@@ -376,16 +359,31 @@ GenericFromScalar(const std::shared_ptr<Scalar>& value) {
   return holder.value;
 }
 
+template <typename T, typename U>
+using enable_if_same_result = enable_if_same<T, U, Result<T>>;
+
 template <typename T>
-static inline enable_if_primitive_ctype<typename EnumTraits<T>::Type, Result<T>>
-GenericFromScalar(const std::shared_ptr<Scalar>& value) {
-  ARROW_ASSIGN_OR_RAISE(auto raw_val,
-                        GenericFromScalar<typename EnumTraits<T>::CType>(value));
-  return ValidateEnumValue<T>(raw_val);
+static inline enable_if_same_result<T, TimeUnit::type> GenericFromScalar(
+    const std::shared_ptr<Scalar>& value) {
+  ARROW_ASSIGN_OR_RAISE(auto raw_val, GenericFromScalar<int32_t>(value));
+  switch (raw_val) {
+    case static_cast<int32_t>(TimeUnit::type::SECOND):
+      return TimeUnit::type::SECOND;
+    case static_cast<int32_t>(TimeUnit::type::MILLI):
+      return TimeUnit::type::MILLI;
+    case static_cast<int32_t>(TimeUnit::type::MICRO):
+      return TimeUnit::type::MICRO;
+    case static_cast<int32_t>(TimeUnit::type::NANO):
+      return TimeUnit::type::NANO;

Review comment:
       Current master actually uses a trait based approach on top of enum; only the value->string conversion need be spelled out: https://github.com/apache/arrow/blob/5889ebb99bb1d13b0a108ddc993f33148651e425/cpp/src/arrow/compute/api_scalar.cc#L56-L74
   
   This PR removes that, but doesn't convert enums outside of arrow::compute, so it spells out explicitly those enums used in FunctionOptions.




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