edponce commented on code in PR #13009:
URL: https://github.com/apache/arrow/pull/13009#discussion_r870292161
##########
cpp/src/arrow/stl_iterator.h:
##########
@@ -128,6 +131,162 @@ class ArrayIterator {
int64_t index_;
};
+template <typename ArrayType,
+ typename ValueAccessor = detail::DefaultValueAccessor<ArrayType>>
+class ChunkedArrayIterator {
+ public:
+ using value_type = arrow::util::optional<typename ValueAccessor::ValueType>;
+ using difference_type = int64_t;
+ using pointer = value_type*;
+ using reference = value_type&;
+ using iterator_category = std::random_access_iterator_tag;
+
+ // Some algorithms need to default-construct an iterator
+ ChunkedArrayIterator() : chunked_array_(NULLPTR), index_(0) {}
+
+ explicit ChunkedArrayIterator(const ChunkedArray& chunked_array, int64_t
index = 0)
+ : chunked_array_(&chunked_array), index_(index) {
+ if (index_ != chunked_array.length()) {
+ auto chunk_location = GetChunkLocation(this->index_);
+ current_array_iterator_ = ArrayIterator<ArrayType>(
+ arrow::internal::checked_cast<const ArrayType&>(
+
*chunked_array_->chunk(static_cast<int>(chunk_location.chunk_index))),
+ chunk_location.index_in_chunk);
+ } else {
+ current_array_iterator_ = {};
+ }
+ }
+
+ // Value access
+ value_type operator*() const { return *current_array_iterator_; }
+
+ value_type operator[](difference_type n) const {
+ auto chunk_location = GetChunkLocation(index_ + n);
+ ArrayIterator<ArrayType> target_iterator{
+ arrow::internal::checked_cast<const ArrayType&>(
+
*chunked_array_->chunk(static_cast<int>(chunk_location.chunk_index)))};
+ return target_iterator[chunk_location.index_in_chunk];
+ }
+
+ int64_t index() const { return index_; }
+
+ // Forward / backward
+ ChunkedArrayIterator& operator++() {
+ (*this) += 1;
+ return *this;
+ }
+ ChunkedArrayIterator& operator--() {
+ (*this) -= 1;
+ return *this;
+ }
+
+ ChunkedArrayIterator operator++(int) {
+ ChunkedArrayIterator tmp(*this);
+ ++*this;
+ return tmp;
+ }
+ ChunkedArrayIterator operator--(int) {
+ ChunkedArrayIterator tmp(*this);
+ --*this;
+ return tmp;
+ }
+
+ // Arithmetic
+ difference_type operator-(const ChunkedArrayIterator& other) const {
+ return index_ - other.index_;
+ }
+ ChunkedArrayIterator operator+(difference_type n) const {
+ return ChunkedArrayIterator(*chunked_array_, index_ + n);
+ }
+ ChunkedArrayIterator operator-(difference_type n) const {
+ return ChunkedArrayIterator(*chunked_array_, index_ - n);
+ }
+ friend inline ChunkedArrayIterator operator+(difference_type diff,
+ const ChunkedArrayIterator&
other) {
+ return ChunkedArrayIterator(*other.chunked_array_, diff + other.index_);
+ }
+ friend inline ChunkedArrayIterator operator-(difference_type diff,
+ const ChunkedArrayIterator&
other) {
+ return ChunkedArrayIterator(*other.chunked_array_, diff - other.index_);
+ }
+ ChunkedArrayIterator& operator+=(difference_type n) {
+ index_ += n;
+ if (index_ != chunked_array_->length()) {
Review Comment:
It seems that any value is valid as long as you can return to the initial
value with its inverse operation. So the check `!=` follows the operation
semantics of a RandomAccessIterator.
Actually, the `<` check would be insufficient because it allows negative
indices (need absolute value of index).
The question now becomes, do Arrow iterators guard against out-of-bounds
accesses?
From a performance perspective, they have basically the same cost.
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