[GitHub] [arrow] bkietz commented on a change in pull request #7279: ARROW-8938: [R] Provide binding for arrow::compute::CallFunction

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

bkietz commented on a change in pull request #7279:
URL: https://github.com/apache/arrow/pull/7279#discussion_r431263416



##########
File path: r/src/compute.cpp
##########
@@ -223,4 +205,66 @@ std::shared_ptr<arrow::Table> Table__FilterChunked(
   }
   return tab;
 }
+
+arrow::Datum to_datum(SEXP x) {
+  // TODO: this is repetitive, can we DRY it out?
+  if (Rf_inherits(x, "ArrowObject") && Rf_inherits(x, "Array")) {
+    Rcpp::ConstReferenceSmartPtrInputParameter<std::shared_ptr<arrow::Array>> obj(x);
+    return static_cast<std::shared_ptr<arrow::Array>>(obj);
+  } else if (Rf_inherits(x, "ArrowObject") && Rf_inherits(x, "ChunkedArray")) {
+    Rcpp::ConstReferenceSmartPtrInputParameter<std::shared_ptr<arrow::ChunkedArray>> obj(x);
+    return static_cast<std::shared_ptr<arrow::ChunkedArray>>(obj);
+  } else if (Rf_inherits(x, "ArrowObject") && Rf_inherits(x, "RecordBatch")) {
+    Rcpp::ConstReferenceSmartPtrInputParameter<std::shared_ptr<arrow::RecordBatch>> obj(x);
+    return static_cast<std::shared_ptr<arrow::RecordBatch>>(obj);
+  } else if (Rf_inherits(x, "ArrowObject") && Rf_inherits(x, "Table")) {
+    Rcpp::ConstReferenceSmartPtrInputParameter<std::shared_ptr<arrow::Table>> obj(x);
+    return static_cast<std::shared_ptr<arrow::Table>>(obj);
+  } else {
+    // TODO: scalar?

Review comment:
       I would recommend refactoring that function into `std::shared_ptr<Scalar> to_scalar(SEXP)`. That function need not be exported (same logic as `Datum`; `SEXP` already holds whatever value). The climax of `to_scalar` should be a call to `arrow::MakeScalar`.
   
   After this:
   ```c++
   std::shared_ptr<ds::Expression> dataset___expr__scalar(SEXP x) {
     return ds::scalar(to_scalar(x));
   }
   ```




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