westonpace commented on a change in pull request #9643:
URL: https://github.com/apache/arrow/pull/9643#discussion_r595521216
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File path: cpp/src/arrow/util/iterator.h
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@@ -44,16 +44,35 @@ struct IterationTraits {
/// \brief a reserved value which indicates the end of iteration. By
/// default this is NULLPTR since most iterators yield pointer types.
/// Specialize IterationTraits if different end semantics are required.
+ ///
+ /// Note: This should not be used to determine if a given value is a
+ /// terminal value. Use IsIterationEnd (which uses IsEnd) instead. This
+ /// is only for returning terminal values.
static T End() { return T(NULLPTR); }
+
+ /// \brief Checks to see if the value is a terminal value.
+ /// A method is used here since T is not neccesarily comparable in many
+ /// cases even though it has a distinct final value
+ static bool IsEnd(const T& val) { return val == End(); }
};
+template <typename T>
+bool IsIterationEnd(const T& val) {
+ return IterationTraits<T>::IsEnd(val);
+}
+
template <typename T>
struct IterationTraits<util::optional<T>> {
/// \brief by default when iterating through a sequence of optional,
/// nullopt indicates the end of iteration.
/// Specialize IterationTraits if different end semantics are required.
static util::optional<T> End() { return util::nullopt; }
+ /// \brief by default when iterating through a sequenc of optional,
Review comment:
Fixed.
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