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Non-domain infrastructure code that is common to many Neo4j components.

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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [https://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * 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
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.cursor;

import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.Supplier;

/**
 * A cursor is an object that moves to point to different locations in a data structure.
 * The abstraction originally comes from mechanical slide rules, which have a "cursor" which
 * slides to point to different positions on the ruler.
 * 
 * Each position a cursor points to is referred to as a "row".
 * 
 * Access to the current row is done by subtyping this interface and adding accessor methods. If no call to
 * {@link #next()} has been done, or if it returned false, then such accessor methods throw {@link
 * IllegalStateException}.
 */
public interface RawCursor extends Supplier, AutoCloseable {
    /**
     * Move the cursor to the next row.
     * Return false if there are no more valid positions, generally indicating that the end of the data structure
     * has been reached.
     */
    boolean next() throws EXCEPTION;

    /**
     * Signal that the cursor is no longer needed.
     */
    @Override
    void close() throws EXCEPTION;

    default void forAll(Consumer consumer) throws EXCEPTION {
        try {
            while (next()) {
                consumer.accept(get());
            }
        } finally {
            close();
        }
    }

    default  R foldl(BiFunction fold, R zero) throws EXCEPTION {
        var last = zero;
        try {
            while (next()) {
                var t = get();
                last = fold.apply(t, last);
            }
        } finally {
            close();
        }
        return last;
    }
}