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.venv/Lib/site-packages/pyarrow/include/arrow/util/map.h

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+// 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 "arrow/result.h"
+
+namespace arrow {
+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 arrow