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/**
* Copyright (C) 2022-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 <absl/container/flat_hash_map.h>
#include <absl/container/flat_hash_set.h>
#include "mongo/base/string_data.h"
#include "mongo/util/assert_util.h"
namespace mongo {
template <typename T>
class PairMapTraits {
public:
using OwnedType = T;
using ViewType = T;
using HashableType = T;
static const T& toOwned(const T& t) {
return t;
}
static const T& toView(const T& t) {
return t;
}
static const T& toHashable(const T& t) {
return t;
}
};
template <>
class PairMapTraits<StringData> {
public:
using OwnedType = std::string;
using ViewType = StringData;
using HashableType = absl::string_view;
static std::string toOwned(const StringData& t) {
return t.toString();
}
static const StringData& toView(const StringData& t) {
return t;
}
static absl::string_view toHashable(const StringData& t) {
// Use the default absl string hasher.
return absl::string_view(t.rawData(), t.size());
}
};
template <>
class PairMapTraits<std::string> {
public:
using OwnedType = std::string;
using ViewType = StringData;
using HashableType = absl::string_view;
static const std::string& toOwned(const std::string& t) {
return t;
}
static StringData toView(const std::string& t) {
return StringData(t);
}
static absl::string_view toHashable(const std::string& t) {
// Use the default absl string hasher.
return absl::string_view(t.data(), t.size());
}
};
/**
* Type that bundles a hashed key with the actual pair value so that hashing can be performed
* outside of insert() call. This is needed to facilitate heterogeneous lookup.
*/
template <typename T1, typename T2>
class PairMapHashedKey {
public:
using OwnedType1 = typename PairMapTraits<T1>::OwnedType;
using OwnedType2 = typename PairMapTraits<T2>::OwnedType;
using OwnedPairType = std::pair<OwnedType1, OwnedType2>;
using ViewType1 = typename PairMapTraits<T1>::ViewType;
using ViewType2 = typename PairMapTraits<T2>::ViewType;
using ViewPairType = std::pair<ViewType1, ViewType2>;
explicit PairMapHashedKey(ViewPairType key, std::size_t hash)
: _key(std::move(key)), _hash(hash) {}
explicit operator OwnedPairType() const {
return {PairMapTraits<ViewType1>::toOwned(_key.first),
PairMapTraits<ViewType2>::toOwned(_key.second)};
}
const ViewPairType& key() const {
return _key;
}
std::size_t hash() const {
return _hash;
}
private:
ViewPairType _key;
std::size_t _hash;
};
/**
* Hasher to support heterogeneous lookup.
*/
template <typename T1, typename T2>
class PairMapHasher {
public:
using OwnedType1 = typename PairMapTraits<T1>::OwnedType;
using OwnedType2 = typename PairMapTraits<T2>::OwnedType;
using OwnedPairType = std::pair<OwnedType1, OwnedType2>;
using ViewType1 = typename PairMapTraits<T1>::ViewType;
using ViewType2 = typename PairMapTraits<T2>::ViewType;
using ViewPairType = std::pair<ViewType1, ViewType2>;
using HashableType1 = typename PairMapTraits<T1>::HashableType;
using HashableType2 = typename PairMapTraits<T2>::HashableType;
using HashablePairType = std::pair<HashableType1, HashableType2>;
// This using directive activates heterogeneous lookup in the hash table.
using is_transparent = void;
std::size_t operator()(const ViewPairType& sd) const {
return absl::Hash<HashablePairType>{}(
std::make_pair(PairMapTraits<ViewType1>::toHashable(sd.first),
PairMapTraits<ViewType2>::toHashable(sd.second)));
}
std::size_t operator()(const OwnedPairType& s) const {
return operator()(std::make_pair(PairMapTraits<OwnedType1>::toView(s.first),
PairMapTraits<OwnedType2>::toView(s.second)));
}
std::size_t operator()(const PairMapHashedKey<T1, T2>& key) const {
return key.hash();
}
PairMapHashedKey<T1, T2> hashed_key(const ViewPairType& sd) const {
return PairMapHashedKey<T1, T2>(sd, operator()(sd));
}
};
template <typename T1, typename T2>
class PairMapEq {
public:
using ViewType1 = typename PairMapTraits<T1>::ViewType;
using ViewType2 = typename PairMapTraits<T2>::ViewType;
using ViewPairType = std::pair<ViewType1, ViewType2>;
// This using directive activates heterogeneous lookup in the hash table.
using is_transparent = void;
bool operator()(const ViewPairType& lhs, const ViewPairType& rhs) const {
return lhs == rhs;
}
bool operator()(const PairMapHashedKey<T1, T2>& lhs, const ViewPairType& rhs) const {
return lhs.key() == rhs;
}
bool operator()(const ViewPairType& lhs, const PairMapHashedKey<T1, T2>& rhs) const {
return lhs == rhs.key();
}
bool operator()(const PairMapHashedKey<T1, T2>& lhs,
const PairMapHashedKey<T1, T2>& rhs) const {
return lhs.key() == rhs.key();
}
};
template <typename K1, typename K2, typename V>
using PairMap = absl::flat_hash_map<std::pair<K1, K2>, V, PairMapHasher<K1, K2>, PairMapEq<K1, K2>>;
template <typename K1, typename K2>
using PairSet = absl::flat_hash_set<std::pair<K1, K2>, PairMapHasher<K1, K2>, PairMapEq<K1, K2>>;
} // namespace mongo
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