indirect.hh

/*
 * This file is open source software, licensed to you under the terms
 * of the Apache License, Version 2.0 (the "License").  See the NOTICE file
 * distributed with this work for additional information regarding copyright
 * ownership.  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.
 */
/*
 * Copyright (C) 2016 ScyllaDB
 */

#pragma once

#include <memory>

namespace seastar {

// This header defines functors for comparing and hashing pointers by pointed-to values instead of pointer addresses.
//
// Examples:
//
//  std::multiset<shared_ptr<sstring>, indirect_less<shared_ptr<sstring>>> _multiset;
//
//  std::unordered_map<shared_ptr<sstring>, bool,
//      indirect_hash<shared_ptr<sstring>>, indirect_equal_to<shared_ptr<sstring>>> _unordered_map;
//

template<typename Pointer, typename Equal = std::equal_to<typename std::pointer_traits<Pointer>::element_type>>
struct indirect_equal_to {
    Equal _eq;
    indirect_equal_to(Equal eq = Equal()) : _eq(std::move(eq)) {}
    bool operator()(const Pointer& i1, const Pointer& i2) const {
        if (bool(i1) ^ bool(i2)) {
            return false;
        }
        return !i1 || _eq(*i1, *i2);
    }
};

template<typename Pointer, typename Less = std::less<typename std::pointer_traits<Pointer>::element_type>>
struct indirect_less {
    Less _cmp;
    indirect_less(Less cmp = Less()) : _cmp(std::move(cmp)) {}
    bool operator()(const Pointer& i1, const Pointer& i2) const {
        if (i1 && i2) {
            return _cmp(*i1, *i2);
        }
        return !i1 && i2;
    }
};

template<typename Pointer, typename Hash = std::hash<typename std::pointer_traits<Pointer>::element_type>>
struct indirect_hash {
    Hash _h;
    indirect_hash(Hash h = Hash()) : _h(std::move(h)) {}
    size_t operator()(const Pointer& p) const {
        if (p) {
            return _h(*p);
        }
        return 0;
    }
};

}