Source/WTF/wtf/text/AtomStringHash.h

/*
 * Copyright (C) 2008-2019 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer. 
 * 2.  Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution. 
 * 3.  Neither the name of Apple Inc. ("Apple") nor the names of
 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission. 
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include <wtf/text/AtomString.h>
#include <wtf/HashTraits.h>

namespace WTF {

    struct AtomStringHash {
        static unsigned hash(const AtomString& key)
        {
            return key.impl()->existingHash();
        }

        static bool equal(const AtomString& a, const AtomString& b)
        {
            return a == b;
        }

        static constexpr bool safeToCompareToEmptyOrDeleted = false;
        static constexpr bool hasHashInValue = true;
    };

    template<> struct HashTraits<WTF::AtomString> : SimpleClassHashTraits<WTF::AtomString> {
        static constexpr bool hasIsEmptyValueFunction = true;
        static bool isEmptyValue(const AtomString& value)
        {
            return value.isNull();
        }

        static void customDeleteBucket(AtomString& value)
        {
            // See unique_ptr's customDeleteBucket() for an explanation.
            ASSERT(!isDeletedValue(value));
            AtomString valueToBeDestroyed = WTFMove(value);
            constructDeletedValue(value);
        }
    };

    template<> struct DefaultHash<AtomString> : AtomStringHash { };
}

using WTF::AtomStringHash;