/*
 * Copyright (c) 2007, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code 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 GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 */
package com.sun.max.collect;

import com.sun.max.*;

/**
 * Defines the semantics of key comparison in a {@linkplain HashMapping hash based data structure} where reference
 * identity is used for {@linkplain #equivalent(Object, Object) equivalence} and the hash code are obtained from
 * {@link System#identityHashCode(Object)}. There is a {@linkplain #instance(Class) singleton} instance of this class.
 */
public final class HashIdentity<T> implements HashEquivalence<T> {

    private HashIdentity() {
    }

    public boolean equivalent(T object1, T object2) {
        return object1 == object2;
    }

    public int hashCode(T object) {
        if (object == null) {
            return 0;
        }
        return System.identityHashCode(object);
    }

    private static final HashIdentity identity = new HashIdentity<>();

    public static <T> HashIdentity<T> instance(Class<HashIdentity<T>> type) {
        return Utils.cast(type, identity);
    }
}