bkietz commented on code in PR #39937:
URL: https://github.com/apache/arrow/pull/39937#discussion_r1478439624
##########
cpp/src/arrow/datum.cc:
##########
@@ -73,86 +74,108 @@ std::shared_ptr<Array> Datum::make_array() const {
}
const std::shared_ptr<DataType>& Datum::type() const {
- if (this->kind() == Datum::ARRAY) {
- return std::get<std::shared_ptr<ArrayData>>(this->value)->type;
- }
- if (this->kind() == Datum::CHUNKED_ARRAY) {
- return std::get<std::shared_ptr<ChunkedArray>>(this->value)->type();
- }
- if (this->kind() == Datum::SCALAR) {
- return std::get<std::shared_ptr<Scalar>>(this->value)->type;
- }
- static std::shared_ptr<DataType> no_type;
- return no_type;
+ return std::visit(
+ [](const auto& value) -> const std::shared_ptr<DataType>& {
+ using T = std::decay_t<decltype(value)>;
+
+ if constexpr (std::is_same_v<T, std::shared_ptr<Scalar>> ||
+ std::is_same_v<T, std::shared_ptr<ArrayData>>) {
+ return value->type;
+ } else if constexpr (std::is_same_v<T, std::shared_ptr<ChunkedArray>>)
{
+ return value->type();
+ } else {
+ static std::shared_ptr<DataType> no_type;
+ return no_type;
Review Comment:
The suggestion results in returning a reference to temporary; unless we
replace the return-by-reference with return-by-value a static variable is
necessary.
We use this pattern in a couple places, I've considered providing a helper
which would make it easier:
```suggestion
return kDefaultRef;
```
```
struct {
template <typename T>
operator const T&() const {
static const T instance;
return instance;
}
} constexpr kDefaultRef;
```
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