westonpace commented on a change in pull request #9095:
URL: https://github.com/apache/arrow/pull/9095#discussion_r564828137
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File path: cpp/src/arrow/util/iterator.h
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@@ -186,6 +187,122 @@ class Iterator : public
util::EqualityComparable<Iterator<T>> {
Result<T> (*next_)(void*) = NULLPTR;
};
+template <typename T>
+struct TransformFlow {
+ using YieldValueType = T;
+
+ TransformFlow(YieldValueType value, bool ready_for_next)
+ : finished_(false),
+ ready_for_next_(ready_for_next),
+ yield_value_(std::move(value)) {}
+ TransformFlow(bool finished, bool ready_for_next)
+ : finished_(finished), ready_for_next_(ready_for_next), yield_value_() {}
+
+ bool HasValue() const { return yield_value_.has_value(); }
+ bool Finished() const { return finished_; }
+ bool ReadyForNext() const { return ready_for_next_; }
+ T Value() const { return *yield_value_; }
+
+ bool finished_ = false;
+ bool ready_for_next_ = false;
+ util::optional<YieldValueType> yield_value_;
+};
+
+struct TransformFinish {
+ template <typename T>
+ operator TransformFlow<T>() && { // NOLINT explicit
+ return TransformFlow<T>(true, true);
+ }
+};
+
+struct TransformSkip {
+ template <typename T>
+ operator TransformFlow<T>() && { // NOLINT explicit
+ return TransformFlow<T>(false, true);
+ }
+};
+
+template <typename T>
+TransformFlow<T> TransformYield(T value = {}, bool ready_for_next = true) {
Review comment:
Needed for the "called again on the same value" case. More in next
comment.
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