milesgranger commented on code in PR #14749:
URL: https://github.com/apache/arrow/pull/14749#discussion_r1034391074
##########
cpp/src/arrow/compute/kernels/scalar_nested.cc:
##########
@@ -131,13 +124,26 @@ struct ListSlice {
list_type->id() == arrow::Type::FIXED_SIZE_LIST);
std::unique_ptr<ArrayBuilder> builder;
+ // should have been checked in resolver
+ // if stop not set, then cannot return fixed size list without input being
fixed size
+ // list b/c we cannot determine the max list element in type resolving.
+ DCHECK(opts.stop.has_value() ||
+ (!opts.stop.has_value() && (!return_fixed_size_list ||
+ list_type->id() ==
arrow::Type::FIXED_SIZE_LIST)));
+
// construct array values
if (return_fixed_size_list) {
- RETURN_NOT_OK(MakeBuilder(
- ctx->memory_pool(),
- fixed_size_list(value_type,
- static_cast<int32_t>(opts.stop.value() -
opts.start)),
- &builder));
+ const auto stop = [&]() {
+ if (opts.stop.has_value()) {
+ return static_cast<int32_t>(opts.stop.value());
+ } else {
+ DCHECK_EQ(list_type->id(), arrow::Type::FIXED_SIZE_LIST);
+ return checked_cast<const
FixedSizeListType*>(list_type)->list_size();
+ }
+ }();
+ const auto size = std::max(stop - static_cast<int32_t>(opts.start), 0);
Review Comment:
This covers the case of your suggested case where `stop` is null and the
fixed size list stop is then set to the list_size, which could be less than the
start.
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