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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <cstddef>
#include <set>
#include <vector>
namespace mongo {
// If non-empty, a vector with size equal to the number of elements in the index key pattern. Each
// element in the vector is an ordered set of positions (starting at 0) into the corresponding
// indexed field that represent what prefixes of the indexed field cause the index to be multikey.
//
// For example, with the index {'a.b': 1, 'a.c': 1} where the paths "a" and "a.b" cause the
// index to be multikey, we'd have a std::vector<std::set<size_t>>{{0U, 1U}, {0U}}.
//
// Further Examples:
// Index PathsThatAreMultiKey MultiKeyPaths
// -------------------- -------------------- --------------------
// {'a.b': 1, 'a.c': 1} "a", "a.b" {{0U, 1U}, {0U}}
// {a: 1, b: 1} "b" {{}, {0U}}
// {a: 1, b: 1} "a" {{0U}, {}}
// {'a.b.c': 1, d: 1} "a.b.c" {{2U}, {}}
// {'a.b': 1, c: 1, d: 1} "a.b", "d" {{1U}, {}, {0U}}
// {a: 1, b: 1} none {{}, {}}
// {a: 1, b: 1} no multikey metadata {}
//
// An empty vector is used to represent that the index doesn't support path-level multikey tracking.
using MultikeyPaths = std::vector<std::set<std::size_t>>;
} // namespace mongo
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