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Library providing immutable/persistent collection classes for Java. While collections are immutable they provide methods for adding and removing values by creating new modified copies of themselves. Each copy shares almost all of its structure with other copies to minimize memory consumption.

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///###////////////////////////////////////////////////////////////////////////
//
// Burton Computer Corporation
// http://www.burton-computer.com
//
// Copyright (c) 2013, Burton Computer Corporation
// All rights reserved.
//
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// modification, are permitted provided that the following conditions are met:
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//     Redistributions of source code must retain the above copyright
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//
//     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
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//     derived from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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package org.javimmutable.collections.cursors;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Cursorable;
import org.javimmutable.collections.Func0;

/**
 * Cursor that creates and returns a real Cursor for a specific iterable only when next() is
 * called for the first time.
 *
 * @param 
 */
public class LazyCursor
        implements Cursor
{
    private final Func0> factory;

    /**
     * Creates a new LazyCursor for the specified factory.
     *
     * @param factory a function to return an actual Cursor to use for iteration
     */
    public LazyCursor(Func0> factory)
    {
        this.factory = factory;
    }

    /**
     * Creates a new LazyCursor for the specified iterable.
     *
     * @param iterable to return an actual Cursor to use for iteration
     */
    public LazyCursor(final Cursorable iterable)
    {
        this.factory = new Func0>()
        {
            @Override
            public Cursor apply()
            {
                return iterable.cursor();
            }
        };
    }

    /**
     * Creates a new LazyPersistentIterator using the specified factory.
     *
     * @param factory a Func0 capable of creating a real Cursor
     */
    public static  LazyCursor of(Func0> factory)
    {
        return new LazyCursor(factory);
    }

    /**
     * Creates a new LazyPersistentIterator for the specified iterable.
     *
     * @param iterable a PersistentIterable capable of producing a non-empty PersistentIterator
     */
    public static  LazyCursor of(Cursorable iterable)
    {
        return new LazyCursor(iterable);
    }

    /**
     * Creates the real cursor using the factory and returns its next() method's result.
     * Thus when the lazy cursor creates the real cursor it always immediately calls its
     * next() method to start its iteration and get it into the state expected by the
     * caller of this method.
     *
     * @return real cursor's next() value
     */
    @Override
    public Cursor next()
    {
        return factory.apply().next();
    }

    /**
     * Always throws IllegalStateException
     *
     * @return never returns
     * @throws IllegalStateException
     */
    @Override
    public boolean hasValue()
    {
        throw new IllegalStateException();
    }

    /**
     * Always throws IllegalStateException
     *
     * @return never returns
     * @throws IllegalStateException
     */
    public V getValue()
    {
        throw new IllegalStateException();
    }
}