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#pragma clang system_header
// 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
#include <utility>
#include "contrib/libs/apache/arrow_next/cpp/src/arrow/result.h"
namespace arrow20 {
namespace internal {
/// Helper providing single-lookup conditional insertion into std::map or
/// std::unordered_map. If `key` exists in the container, an iterator to that pair
/// will be returned. If `key` does not exist in the container, `gen(key)` will be
/// invoked and its return value inserted.
template <typename Map, typename Gen>
auto GetOrInsertGenerated(Map* map, typename Map::key_type key, Gen&& gen)
-> decltype(map->begin()->second = gen(map->begin()->first), map->begin()) {
decltype(gen(map->begin()->first)) placeholder{};
auto it_success = map->emplace(std::move(key), std::move(placeholder));
if (it_success.second) {
// insertion of placeholder succeeded, overwrite it with gen()
const auto& inserted_key = it_success.first->first;
auto* value = &it_success.first->second;
*value = gen(inserted_key);
}
return it_success.first;
}
template <typename Map, typename Gen>
auto GetOrInsertGenerated(Map* map, typename Map::key_type key, Gen&& gen)
-> Result<decltype(map->begin()->second = gen(map->begin()->first).ValueOrDie(),
map->begin())> {
decltype(gen(map->begin()->first).ValueOrDie()) placeholder{};
auto it_success = map->emplace(std::move(key), std::move(placeholder));
if (it_success.second) {
// insertion of placeholder succeeded, overwrite it with gen()
const auto& inserted_key = it_success.first->first;
auto* value = &it_success.first->second;
ARROW_ASSIGN_OR_RAISE(*value, gen(inserted_key));
}
return it_success.first;
}
} // namespace internal
} // namespace arrow20
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