[GitHub] [arrow] wesm commented on a diff in pull request #13397: ARROW-16444: [R] Implement user-defined scalar functions in R bindings

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

wesm commented on code in PR #13397:
URL: https://github.com/apache/arrow/pull/13397#discussion_r902624010


##########
r/src/compute.cpp:
##########
@@ -574,3 +576,118 @@ SEXP compute__CallFunction(std::string func_name, cpp11::list args, cpp11::list
 std::vector<std::string> compute__GetFunctionNames() {
   return arrow::compute::GetFunctionRegistry()->GetFunctionNames();
 }
+
+class RScalarUDFCallable : public arrow::compute::ArrayKernelExec {

Review Comment:
   Please do this a different way (e.g. put the data that you need to persist in a KernelState instead). `ArrayKernelExec` is a `std::function` and is meant to have the semantics of a function pointer, not a generic callable. I actually plan to make `ArrayKernelExec` a function pointer because debugging with `std::function` adds ~4 levels to the call stack when using gdb which is very tedious



##########
r/src/compute.cpp:
##########
@@ -574,3 +576,118 @@ SEXP compute__CallFunction(std::string func_name, cpp11::list args, cpp11::list
 std::vector<std::string> compute__GetFunctionNames() {
   return arrow::compute::GetFunctionRegistry()->GetFunctionNames();
 }
+
+class RScalarUDFCallable : public arrow::compute::ArrayKernelExec {

Review Comment:
   Please do this a different way (e.g. put the data that you need to persist in a KernelState instead). `ArrayKernelExec` is a `std::function` and is meant to have the semantics of a function pointer, not a generic callable class. I actually plan to make `ArrayKernelExec` a function pointer because debugging with `std::function` adds ~4 levels to the call stack when using gdb which is very tedious



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