bkietz commented on code in PR #40687:
URL: https://github.com/apache/arrow/pull/40687#discussion_r1532504328
##########
cpp/src/arrow/compute/kernels/scalar_compare.cc:
##########
@@ -705,6 +705,14 @@ struct BinaryScalarMinMax {
template <typename Op>
struct FixedSizeBinaryScalarMinMax {
static Status Exec(KernelContext* ctx, const ExecSpan& batch, ExecResult*
out) {
+ if (batch.IsNull()) {
+ std::shared_ptr<Scalar> result =
MakeNullScalar(out->type()->GetSharedPtr());
+ ARROW_ASSIGN_OR_RAISE(std::shared_ptr<Array> arr_result,
+ MakeArrayFromScalar(*result, 1));
+ out->value = std::move(arr_result->data());
Review Comment:
This factory allocates and so should use the pool provided by the kernel
context. Also this can be written more concisely with MakeArrayOfNull
```suggestion
ARROW_ASSIGN_OR_RAISE(out->value,
MakeArrayOfNull(out->type()->GetSharedPtr(), 1
ctx->memory_pool()));
```
##########
cpp/src/arrow/compute/kernels/scalar_random.cc:
##########
@@ -57,6 +57,14 @@ random::pcg64_oneseq MakeSeedGenerator() {
}
Status ExecRandom(KernelContext* ctx, const ExecSpan& batch, ExecResult* out) {
+ if (batch.IsNull()) {
Review Comment:
Since random is not a pure function, it should not return scalar like this.
##########
cpp/src/arrow/compute/exec_test.cc:
##########
@@ -1425,6 +1426,33 @@ TEST(Ordering, IsSuborderOf) {
CheckOrdering(unordered, {true, true, true, true, true, true});
}
+static Status RegisterMyScalarPureFunction() {
+ const std::string name = "my_scalar_function";
+ auto func = std::make_shared<ScalarFunction>(name, Arity::Nullary(),
+ FunctionDoc::Empty(), nullptr);
+ auto func_exec = [](KernelContext* /*ctx*/, const ExecSpan& /*batch*/,
+ ExecResult* out) -> Status {
+ auto scalar = MakeScalar("I am a scalar");
+ ARROW_ASSIGN_OR_RAISE(auto arr_res, MakeArrayFromScalar(*scalar, 1));
+ out->value = std::move(arr_res->data());
+ return Status::OK();
+ };
+
+ ScalarKernel kernel({}, utf8(), func_exec);
+ ARROW_RETURN_NOT_OK(func->AddKernel(kernel));
+
+ auto registry = GetFunctionRegistry();
+ ARROW_RETURN_NOT_OK(registry->AddFunction(std::move(func)));
+ return Status::OK();
+}
+
+TEST(CallFunction, ScalarPureFunction) {
+ ASSERT_OK(RegisterMyScalarPureFunction());
+
+ EXPECT_THAT(CallFunction("my_scalar_function", ExecBatch({})),
+ ResultWith(MakeScalar("I am a scalar")));
+}
Review Comment:
I don't think this test is relevant to the PR. "my_scalar_function" returns
only scalar in any case
##########
cpp/src/arrow/compute/exec.h:
##########
@@ -257,6 +257,10 @@ struct ARROW_EXPORT ExecBatch {
return result;
}
+ /// \brief A check for the empty ExecBatch with no output length
+ /// and function's arguments.
+ bool IsNull() const { return length == 0 && num_values() == 0; }
Review Comment:
Under what circumstances would we have `num_values() == 0` but `length !=
0`? It seems accessing the length of an ExecBatch with no values would be ill
formed and we could forgo `IsValid()` in favor of just checking `num_values()
== 0`
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