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d5ddd14ee1
Add MapInsertOrReplace<>() to insert a key-value pair into a map if the key is not already present, or replace the existing value for key if the key is present. The original value can optionally be returned to the caller in this case. Map insertions now use either MapInsertOrReplace<>() or std::map<>::insert() directly. Use MapInsertOrReplace<>() when the map should be updated to contain a mapping from a key to a value regardless of whether the key is already present. Use std::map<>::insert() to insert a mapping from a key to a value without replacing any existing mapping from a key, if present. If it is important to know whether an existing mapping from a key was present, use the returned std::pair<>.second. If it is important to know the existing value, use the returned std::pair<>.first->second. This change has a slight positive impact on performance. TEST=crashpad_util_test MapInsert.MapInsertOrReplace and others BUG= R=scottmg@chromium.org Review URL: https://codereview.chromium.org/1044273002
57 lines
2.1 KiB
C++
57 lines
2.1 KiB
C++
// Copyright 2015 The Crashpad Authors. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// 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, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef CRASHPAD_UTIL_STDLIB_MAP_INSERT_H_
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#define CRASHPAD_UTIL_STDLIB_MAP_INSERT_H_
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#include <map>
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#include <utility>
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namespace crashpad {
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//! \brief Inserts a mapping from \a key to \a value into \a map, or replaces
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//! an existing mapping so that \a key maps to \value.
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//!
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//! This behaves similarly to `std::map<>::insert_or_assign()` proposed for
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//! C++17, except that the \a old_value parameter is added.
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//!
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//! \param[inout] map The map to operate on.
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//! \param[in] key The key that should be mapped to \a value.
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//! \param[in] value The value that \a key should map to.
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//! \param[out] old_value If \a key was previously present in \a map, this will
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//! be set to its previous value. This parameter is optional and may be
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//! `nullptr` if this information is not required.
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//!
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//! \return `false` if \a key was previously present in \a map. If \a old_value
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//! is not `nullptr`, it will be set to the previous value. `true` if \a
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//! key was not present in the map and was inserted.
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template <typename T>
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bool MapInsertOrReplace(T* map,
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const typename T::key_type& key,
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const typename T::mapped_type& value,
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typename T::mapped_type* old_value) {
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const auto result = map->insert(std::make_pair(key, value));
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if (!result.second) {
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if (old_value) {
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*old_value = result.first->second;
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}
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result.first->second = value;
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}
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return result.second;
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}
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} // namespace crashpad
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#endif // CRASHPAD_UTIL_STDLIB_MAP_INSERT_H_
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