[GitHub] [arrow] pitrou commented on a change in pull request #10817: ARROW-9434: [C++] Store type code in UnionScalar

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

pitrou commented on a change in pull request #10817:
URL: https://github.com/apache/arrow/pull/10817#discussion_r677707357



##########
File path: cpp/src/arrow/scalar.cc
##########
@@ -310,6 +316,19 @@ struct MakeNullImpl {
     return Status::OK();
   }
 
+  Status Visit(const SparseUnionType& type) { return MakeUnionScalar(type); }
+
+  Status Visit(const DenseUnionType& type) { return MakeUnionScalar(type); }
+
+  template <typename T, typename ScalarType = typename TypeTraits<T>::ScalarType>
+  Status MakeUnionScalar(const T& type) {
+    if (type.num_fields() == 0) {
+      return Status::Invalid("Cannot make scalar of empty union type");
+    }
+    out_ = std::make_shared<ScalarType>(type.type_codes()[0], type_);

Review comment:
       It was already the case, this is basically adding the type code parameter.
   I agree this behaviour is debatable.




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