staying neutral

Quite some time ago, there was the idea of a DualIterator for PHP's SPL extension.

But right after providing it, I had to learn that allowing two sub Iterators only is too limiting. So when I got asked by Johannes what open TODOs I have left for upcoming PHP 5.3, I thought of it again. He even offered me a PHP implementation of his own. And he did not hesitate to tell me that he would rather see it use SplObjectStorage to store sub Iterators, rather than the Array he used. As he also allowed associative information to be stored along with sub Iterators, I sat down today to add this feature in SplObjectStorage. Having added that, I came up with the below implementation. Now, if anyone is interested, then please help in testing this out. If you do so, please put your tests in phpt format and send me your tests.

<?php
/** @file appenditerator.inc
 * @ingroup SPL
 * @brief class MultipleIterator
 * @author  Johannes Schlueter
 * @author  Marcus Boerger
 * @date    2003 - 2008
 *
 * SPL - Standard PHP Library
 */

/** @ingroup SPL
 * @brief   Iterator that iterates over several iterators one after the other
 * @author  Johannes Schlueter
 * @author  Marcus Boerger
 * @version 1.0
 * @since PHP 5.3
 */
class MultipleIterator implements Iterator {
    /** Inner Iterators */
    private $iterators;

    /** Flags: const MIT_* */
    private $flags;

    /** do not require all sub iterators to be valid in iteration */
    const MIT_NEED_ANY = 0;

    /** require all sub iterators to be valid in iteration */
    const MIT_NEED_ALL  = 1;

    /** keys are created from sub iterators position */
    const MIT_KEYS_NUMERIC  = 0;

    /** keys are created from sub iterators associated infromation */
    const MIT_KEYS_ASSOC  = 2;

    /** Construct a new empty MultipleIterator
     * @param flags MIT_* flags
     */
    public function __construct($flags = self::MIT_NEED_ALL|self::MIT_KEYS_NUMERIC)
    {
        $this->iterators = new SplObjectStorage();
        $this->flags = $flags;
    }

    /** @return current flags MIT_* */
    public function getFlags()
    {
        return $this->flags;
    }

    /** @param $flags new flags. */
    public function setFlags($flags)
    {
        $this->flags = $flags;
    }

    /** @param $iter new Iterator to attach.
     * @param $inf associative info forIteraotr, must be NULL, integer or string
     *
     * @throws IllegalValueException if a inf is none of NULL, integer or string
     * @throws IllegalValueException if a inf is already an associated info
     */
    public function attachIterator(Iterator $iter, $inf = NULL)
    {
        
        if (!is_null($inf))
        {
            if (!is_int($inf) && !is_string($inf))
            {
                throw new IllegalValueException('Inf must be NULL, integer or string');
            }
            foreach($this->iterators as $iter)
            {
                if ($inf == $this->iterators->getInfo())
                {
                    throw new IllegalValueException('Key duplication error');
                }
            }
        }
        $this->iterators->attach($iter, $inf);
    }

    /** @param $iter attached Iterator that should be detached. */
    public function detachIterator(Iterator $iter)
    {
        $this->iterators->detach($iter);
    }

    /** @param $iter Iterator to check
    * @return whether $iter is attached or not
    */
    public function containsIterator(Iterator $iter)
    {
        return $this->iterator->contains($iter);
    }

    /** @return number of attached Iterator instances. */
    public function countIterators()
    {
        return $this->iterators->count();
    }

    /** Rewind all attached Iterator instances. */
    public function rewind()
    {
        foreach($this->iterators as $iter)
        {
            $iter->rewind();
        }
    }

    /**
    * @return whether all or one sub iterator is valid depending on flags.
    * In mode MIT_NEED_ALL we expect all sub iterators to be valid and
    * return flase on the first non valid one. If that flag is not set we
    * return true on the first valid sub iterator found. If no Iterator
    * is attached, we always return false.
    */
    public function valid()
    {
        if (!sizeof($this->iterators)) {
            return false;
        }
        // The following code is an optimized version that executes as few
        // valid() calls as necessary and that only checks the flags once.
        $expect = $this->flags & self::MIT_NEED_ALL ? true : false;
        foreach($this->iterators as $iter)
        {
            if ($expect != $iter->valid())
            {
                return !$expect;
            }
        }
        return $expect;
    }

    /** Move all attached Iterator instances forward. That is invoke
    * their next() method regardless of their state.
    */
    public function next()
    {
        foreach($this->iterators as $iter)
        {
            $iter->next();
        }
    }

    /** @return false if no sub Iterator is attached and an array of
    * all registered Iterator instances current() result.
    * @throws RuntimeException      if mode MIT_NEED_ALL is set and at least one
    *                               attached Iterator is not valid().
    * @throws IllegalValueException if a key is NULL and MIT_KEYS_ASSOC is set.
    */
    public function current()
    {
        if (!sizeof($this->iterators))
        {
            return false;
        }
        $retval = array();
        foreach($this->iterators as $iter)
        {
            if ($it->valid())
            {
                if ($this->flags & self::MIT_KEYS_ASSOC)
                {
                    $key = $this->iterators->getInfo();
                    if (is_null($key))
                    {
                        throw new IllegalValueException('Sub-Iterator is associated with NULL');
                    }
                    $retval[$key] = $iter->current();
                }
                else
                {
                    $retval[] = $iter->current();
                }
            }
            else if ($this->flags & self::MIT_NEED_ALL)
            {
                throw new RuntimeException('Called current() with non valid sub iterator');
            }
            else
            {
                $retval[] = NULL;
            }
        }
        return $retval;
    }

    /** @return false if no sub Iterator is attached and an array of
    * all registered Iterator instances key() result.
    * @throws LogicException if mode MIT_NEED_ALL is set and at least one
    *         attached Iterator is not valid().
    */
    public function key()
    {
        if (!sizeof($this->iterators))
        {
            return false;
        }
        $retval = array();
        foreach($this->iterators as $iter)
        {
            if ($it->valid())
            {
                $retval[] = $iter->key();
            }
            else if ($this->flags & self::MIT_NEED_ALL)
            {
                throw new LogicException('Called key() with non valid sub iterator');
            }
            else
            {
                $retval[] = NULL;
            }
        }
        return $retval;
    }
}




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