[GitHub] [arrow] bkietz commented on a change in pull request #10472: ARROW-12975: [C++][Python] if_else kernel doesn't support upcasting

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

bkietz commented on a change in pull request #10472:
URL: https://github.com/apache/arrow/pull/10472#discussion_r646894778



##########
File path: cpp/src/arrow/compute/kernels/scalar_if_else.cc
##########
@@ -543,7 +543,37 @@ struct ResolveIfElseExec {
   }
 };
 
-void AddPrimitiveIfElseKernels(const std::shared_ptr<ScalarFunction>& scalar_function,
+struct IfElseFunction : ScalarFunction {
+  using ScalarFunction::ScalarFunction;
+
+  Result<const Kernel*> DispatchBest(std::vector<ValueDescr>* values) const override {
+    RETURN_NOT_OK(CheckArity(*values));
+
+    // if-else 0'th descriptor is bool
+    std::vector<ValueDescr> left_right{(*values)[1], (*values)[2]};
+
+    using arrow::compute::detail::DispatchExactImpl;
+    if (auto kernel = DispatchExactImpl(this, *values)) return kernel;
+
+    //    internal::EnsureDictionaryDecoded(values);
+
+    if (values->size() == 3) {
+      internal::ReplaceNullWithOtherType(&left_right);
+
+      if (auto type = internal::CommonNumeric(left_right)) {
+        internal::ReplaceTypes(type, &left_right);
+      }
+    }
+
+    if (auto kernel =
+            DispatchExactImpl(this, {(*values)[0], left_right[0], left_right[1]})) {
+      return kernel;
+    }

Review comment:
       ```suggestion
       using arrow::compute::detail::DispatchExactImpl;
       if (auto kernel = DispatchExactImpl(this, *values)) return kernel;
   
       internal::EnsureDictionaryDecoded(values);
   
       // condition argument must be bool
       auto cond_shape = values->at(0).shape();
       values->pop_front();
   
       internal::ReplaceNullWithOtherType(values);
       if (auto type = internal::CommonNumeric(*values)) {
         internal::ReplaceTypes(type, values);
       }
       values->push_front(ValueDescr{boolean(), cond_shape});
   
       if (auto kernel = DispatchExactImpl(this, *values)) {
         return kernel;
       }
   ```




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