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package org.javimmutable.collections;

import javax.annotation.Nonnull;
import java.util.Iterator;
import java.util.Spliterator;

/**
 * Merges the concepts of Spliterator and Iterator.  Objects implementing this
 * interface are Iterators that are capable of splitting into two parts under
 * certain conditions and are also capable of creating Spliterators on demand.
 */
public interface SplitableIterator
    extends Iterator
{
    /**
     * Tests to determine if this Iterator is capable of splitting into two new Iterators.
     */
    default boolean isSplitAllowed()
    {
        return false;
    }

    /**
     * Whenever isSplitAllowed returns true this method can be used to create two new
     * SplitableIterators that collectively visit all the same elements as this Iterator.
     * Whenever isSplitAllowed returns false this method throws UnsupportedOperationException.
     *
     * @return two new SplitableIterators spanning the same elements as this
     * @throws UnsupportedOperationException if splitting is not allowed
     */
    @Nonnull
    default SplitIterator splitIterator()
    {
        throw new UnsupportedOperationException();
    }

    /**
     * Utility method that creates a Spliterator with the specified characteristics that
     * encounters all of the same elements as this Iterator.  Implementations are allowed
     * to link the Spliterator to use this Iterator directly.
     */
    @Nonnull
    Spliterator spliterator(int characteristics);
}