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64 lines
2.4 KiB
C++
64 lines
2.4 KiB
C++
// Licensed to the Apache Software Foundation (ASF) under one
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// or more contributor license agreements. See the NOTICE file
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// distributed with this work for additional information
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// regarding copyright ownership. The ASF licenses this file
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// to you under the Apache License, Version 2.0 (the
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// "License"); you may not use this file except in compliance
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// with the License. You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing,
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// software distributed under the License is distributed on an
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// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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// KIND, either express or implied. See the License for the
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// specific language governing permissions and limitations
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// under the License.
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#pragma once
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#include <utility>
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#include "arrow/result.h"
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namespace arrow {
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namespace internal {
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/// Helper providing single-lookup conditional insertion into std::map or
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/// std::unordered_map. If `key` exists in the container, an iterator to that pair
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/// will be returned. If `key` does not exist in the container, `gen(key)` will be
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/// invoked and its return value inserted.
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template <typename Map, typename Gen>
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auto GetOrInsertGenerated(Map* map, typename Map::key_type key, Gen&& gen)
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-> decltype(map->begin()->second = gen(map->begin()->first), map->begin()) {
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decltype(gen(map->begin()->first)) placeholder{};
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auto it_success = map->emplace(std::move(key), std::move(placeholder));
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if (it_success.second) {
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// insertion of placeholder succeeded, overwrite it with gen()
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const auto& inserted_key = it_success.first->first;
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auto* value = &it_success.first->second;
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*value = gen(inserted_key);
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}
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return it_success.first;
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}
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template <typename Map, typename Gen>
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auto GetOrInsertGenerated(Map* map, typename Map::key_type key, Gen&& gen)
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-> Result<decltype(map->begin()->second = gen(map->begin()->first).ValueOrDie(),
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map->begin())> {
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decltype(gen(map->begin()->first).ValueOrDie()) placeholder{};
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auto it_success = map->emplace(std::move(key), std::move(placeholder));
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if (it_success.second) {
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// insertion of placeholder succeeded, overwrite it with gen()
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const auto& inserted_key = it_success.first->first;
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auto* value = &it_success.first->second;
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ARROW_ASSIGN_OR_RAISE(*value, gen(inserted_key));
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}
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return it_success.first;
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}
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} // namespace internal
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} // namespace arrow
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