felipecrv commented on code in PR #41827:
URL: https://github.com/apache/arrow/pull/41827#discussion_r1623506157
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cpp/src/arrow/compute/kernels/scalar_cast_string.cc:
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@@ -510,6 +510,60 @@ void AddBinaryToFixedSizeBinaryCast(CastFunction* func) {
AddBinaryToFixedSizeBinaryCast<FixedSizeBinaryType>(func);
}
+// ----------------------------------------------------------------------
+// Union to String
+
+template <typename O>
+struct UnionToStringCastFunctor {
+ using BuilderType = typename TypeTraits<O>::BuilderType;
+
+ static Status Exec(KernelContext* ctx, const ExecSpan& batch, ExecResult*
out) {
+ const ArraySpan& input = batch[0].array;
+ const auto& union_type = checked_cast<const UnionType&>(*input.type);
+ const auto type_ids = input.GetValues<int8_t>(1);
+ const auto& offsets = input.GetValues<int32_t>(2);
+
+ BuilderType builder(input.type->GetSharedPtr(), ctx->memory_pool());
+ RETURN_NOT_OK(builder.Reserve(input.length));
+
+ for (int64_t i = 0; i < input.length; ++i) {
+ if (input.IsNull(i)) {
+ RETURN_NOT_OK(builder.AppendNull());
+ continue;
+ }
+
+ const int8_t type_id = type_ids[i];
+ const auto& field = union_type.field(union_type.child_ids()[type_id]);
+ const ArraySpan& child_span =
input.child_data[union_type.child_ids()[type_id]];
+
+ std::shared_ptr<Scalar> child_scalar;
+ auto child_index = union_type.mode() == UnionMode::DENSE ? offsets[i] :
i;
Review Comment:
This should be a template parameter (a `UnionMode::type`) so we can
specialize with `if constexpr` checks in the loop.
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