Copilot commented on code in PR #905: URL: https://github.com/apache/iceberg-cpp/pull/905#discussion_r3930316814
########## src/iceberg/util/iterator.h: ########## @@ -0,0 +1,128 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, + * software distributed under the License is distributed on an + * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY + * KIND, either express or implied. See the License for the + * specific language governing permissions and limitations + * under the License. + */ + +#pragma once + +/// \file iceberg/util/iterator.h +/// \brief Pull-based iterator interface for fallible, lazily produced values. + +#include <deque> +#include <optional> +#include <type_traits> +#include <utility> +#include <vector> + +#include "iceberg/result.h" + +namespace iceberg { + +/// \brief A pull-based iterator whose reads may fail. +/// +/// Iterator implementations own any resources needed to produce values. Destroying an +/// iterator releases those resources, including when iteration stops before reaching the +/// end. Iterators are not thread-safe unless an implementation explicitly says otherwise. +/// Once Next() returns an error or std::nullopt, the iterator is terminal. Subsequent +/// calls return the same terminal result without invoking the implementation again. +/// +/// \tparam T Value returned by the iterator. +template <typename T> +class Iterator { + public: + virtual ~Iterator() = default; + + Iterator() = default; + Iterator(const Iterator&) = delete; + Iterator& operator=(const Iterator&) = delete; + Iterator(Iterator&&) noexcept = default; + Iterator& operator=(Iterator&&) noexcept = default; + + /// \brief Return the next value, or std::nullopt when the iterator is exhausted. + /// + /// After this method returns an error or std::nullopt, subsequent calls return the same + /// terminal result without invoking NextImpl(). + Result<std::optional<T>> Next() { + if (error_.has_value()) { + return std::unexpected(*error_); + } + if (finished_) { + return std::nullopt; + } + + auto result = NextImpl(); + if (!result.has_value()) { + error_ = result.error(); + } else if (!result.value().has_value()) { + finished_ = true; + } + return result; + } + + /// \brief Consume the remaining values into a vector. + Result<std::vector<T>> ToVector() { + auto collect = [this](auto& values, auto append, + auto finish) -> Result<std::vector<T>> { + while (true) { + auto result = Next(); + if (!result.has_value()) { + return std::unexpected(std::move(result.error())); + } + auto& value = result.value(); + if (!value.has_value()) { + return finish(values); + } + append(values, value.value()); + } + }; + + if constexpr (!std::is_move_constructible_v<T>) { + static_assert(std::is_copy_constructible_v<T>, + "Iterator::ToVector requires T to be move- or copy-constructible"); + + // Stage copy-only values in a deque to avoid copying previously collected + // values during growth, then allocate the final vector storage once. + std::deque<T> values; + return collect( + values, [](auto& destination, const T& value) { destination.push_back(value); }, + [](const auto& source) { + return std::vector<T>(source.cbegin(), source.cend()); + }); + } else { Review Comment: The copy-only ToVector() path stages into a std::deque and then copies again into the final std::vector, which guarantees an extra full copy of all collected elements (in addition to the per-element copy when appending). Since std::vector supports reallocation via copying when T is copy-constructible, collecting directly into a vector avoids that second pass while still supporting copy-only types. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
