felipecrv commented on code in PR #41894:
URL: https://github.com/apache/arrow/pull/41894#discussion_r1635688147
##########
cpp/src/arrow/util/formatting.h:
##########
@@ -652,5 +654,82 @@ class StringFormatter<MonthDayNanoIntervalType> {
}
};
+template <>
+class StringFormatter<BaseListScalar> {
+ public:
+ explicit StringFormatter(const DataType* type) : type_(type) {}
+
+ using value_type = BaseListScalar;
+
+ template <typename Appender>
+ Return<Appender> operator()(const BaseListScalar& value, Appender&& append) {
+ std::stringstream ss;
+ ss << type_->ToString() << "[";
+ for (int64_t i = 0; i < value.value->length(); i++) {
+ if (i > 0) ss << ", ";
+ auto item = value.value->GetScalar(i);
Review Comment:
We shouldn't allocate one scalar per entry of an array in a loop. The
virtual-dispatching string formatters should have an initialization phase and
then you ask it (via a virtual method) to convert value at position `i` and
append it into `std::string *out_appender`.
I will sketch this out and open a draft PR, so you can checkout my branch
and implement it for all the nested types. Is that cool with you?
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