设计模式php实例：迭代器模式

迭代器模式提供一种访问一个容器对象中的各个元素，而又不暴露其内部细节的方法。在应用中，我们时常会遇到各种变量代码，foreach在很多代码处都可以见到，使用迭代器可以对不同数据结构的集合封装，外部只需调用迭代器提供的接口即可，提高了应用的可扩展性。

迭代器UML类图

PHP SPL中提供了迭代器接口Iterator和容器接口IteatorAggragate

YII代码实例：

class CListIterator implements Iterator
{
	/**
	 * @var array the data to be iterated through
	 */
	private $_d;
	/**
	 * @var integer index of the current item
	 */
	private $_i;
	/**
	 * @var integer count of the data items
	 */
	private $_c;

	/**
	 * Constructor.
	 * @param array $data the data to be iterated through
	 */
	public function __construct(&$data)//数组引用传递
	{
		$this->_d=&$data;
		$this->_i=0;
		$this->_c=count($this->_d);
	}

	/**
	 * Rewinds internal array pointer.
	 * This method is required by the interface Iterator.
	 */
	public function rewind()
	{
		$this->_i=0;
	}

	/**
	 * Returns the key of the current array item.
	 * This method is required by the interface Iterator.
	 * @return integer the key of the current array item
	 */
	public function key()
	{
		return $this->_i;
	}

	/**
	 * Returns the current array item.
	 * This method is required by the interface Iterator.
	 * @return mixed the current array item
	 */
	public function current()
	{
		return $this->_d[$this->_i];
	}

	/**
	 * Moves the internal pointer to the next array item.
	 * This method is required by the interface Iterator.
	 */
	public function next()
	{
		$this->_i++;
	}

	/**
	 * Returns whether there is an item at current position.
	 * This method is required by the interface Iterator.
	 * @return boolean
	 */
	public function valid()
	{
		return $this->_i<$this->_c;
	}
}

class CList extends CComponent implements IteratorAggregate,ArrayAccess,Countable
{
	/**
	 * @var array internal data storage
	 */
	private $_d=array();
	/**
	 * @var integer number of items
	 */
	private $_c=0;
	/**
	 * @var boolean whether this list is read-only
	 */
	private $_r=false;

	/**
	 * Constructor.
	 * Initializes the list with an array or an iterable object.
	 * @param array $data the initial data. Default is null, meaning no initialization.
	 * @param boolean $readOnly whether the list is read-only
	 * @throws CException If data is not null and neither an array nor an iterator.
	 */
	public function __construct($data=null,$readOnly=false)
	{
		if($data!==null)
			$this->copyFrom($data);
		$this->setReadOnly($readOnly);
	}

	/**
	 * @return boolean whether this list is read-only or not. Defaults to false.
	 */
	public function getReadOnly()
	{
		return $this->_r;
	}

	/**
	 * @param boolean $value whether this list is read-only or not
	 */
	protected function setReadOnly($value)
	{
		$this->_r=$value;
	}

	/**
	 * Returns an iterator for traversing the items in the list.
	 * This method is required by the interface IteratorAggregate.
	 * @return Iterator an iterator for traversing the items in the list.
	 */
	public function getIterator()
	{
		return new CListIterator($this->_d);
	}

	/**
	 * Returns the number of items in the list.
	 * This method is required by Countable interface.
	 * @return integer number of items in the list.
	 */
	public function count()
	{
		return $this->getCount();
	}

	/**
	 * Returns the number of items in the list.
	 * @return integer the number of items in the list
	 */
	public function getCount()
	{
		return $this->_c;
	}

	/**
	 * Returns the item at the specified offset.
	 * This method is exactly the same as {@link offsetGet}.
	 * @param integer $index the index of the item
	 * @return mixed the item at the index
	 * @throws CException if the index is out of the range
	 */
	public function itemAt($index)
	{
		if(isset($this->_d[$index]))
			return $this->_d[$index];
		else if($index>=0 && $index<$this->_c) // in case the value is null
			return $this->_d[$index];
		else
			throw new CException(Yii::t('yii','List index "{index}" is out of bound.',
				array('{index}'=>$index)));
	}

	/**
	 * Appends an item at the end of the list.
	 * @param mixed $item new item
	 * @return integer the zero-based index at which the item is added
	 */
	public function add($item)
	{
		$this->insertAt($this->_c,$item);
		return $this->_c-1;
	}

	/**
	 * Inserts an item at the specified position.
	 * Original item at the position and the next items
	 * will be moved one step towards the end.
	 * @param integer $index the specified position.
	 * @param mixed $item new item
	 * @throws CException If the index specified exceeds the bound or the list is read-only
	 */
	public function insertAt($index,$item)
	{
		if(!$this->_r)
		{
			if($index===$this->_c)
				$this->_d[$this->_c++]=$item;
			else if($index>=0 && $index<$this->_c)
			{
				array_splice($this->_d,$index,0,array($item));
				$this->_c++;
			}
			else
				throw new CException(Yii::t('yii','List index "{index}" is out of bound.',
					array('{index}'=>$index)));
		}
		else
			throw new CException(Yii::t('yii','The list is read only.'));
	}

	/**
	 * Removes an item from the list.
	 * The list will first search for the item.
	 * The first item found will be removed from the list.
	 * @param mixed $item the item to be removed.
	 * @return integer the index at which the item is being removed
	 * @throws CException If the item does not exist
	 */
	public function remove($item)
	{
		if(($index=$this->indexOf($item))>=0)
		{
			$this->removeAt($index);
			return $index;
		}
		else
			return false;
	}

	/**
	 * Removes an item at the specified position.
	 * @param integer $index the index of the item to be removed.
	 * @return mixed the removed item.
	 * @throws CException If the index specified exceeds the bound or the list is read-only
	 */
	public function removeAt($index)
	{
		if(!$this->_r)
		{
			if($index>=0 && $index<$this->_c)
			{
				$this->_c--;
				if($index===$this->_c)
					return array_pop($this->_d);
				else
				{
					$item=$this->_d[$index];
					array_splice($this->_d,$index,1);
					return $item;
				}
			}
			else
				throw new CException(Yii::t('yii','List index "{index}" is out of bound.',
					array('{index}'=>$index)));
		}
		else
			throw new CException(Yii::t('yii','The list is read only.'));
	}

	/**
	 * Removes all items in the list.
	 */
	public function clear()
	{
		for($i=$this->_c-1;$i>=0;--$i)
			$this->removeAt($i);
	}

	/**
	 * @param mixed $item the item
	 * @return boolean whether the list contains the item
	 */
	public function contains($item)
	{
		return $this->indexOf($item)>=0;
	}

	/**
	 * @param mixed $item the item
	 * @return integer the index of the item in the list (0 based), -1 if not found.
	 */
	public function indexOf($item)
	{
		if(($index=array_search($item,$this->_d,true))!==false)
			return $index;
		else
			return -1;
	}

	/**
	 * @return array the list of items in array
	 */
	public function toArray()
	{
		return $this->_d;
	}

	/**
	 * Copies iterable data into the list.
	 * Note, existing data in the list will be cleared first.
	 * @param mixed $data the data to be copied from, must be an array or object implementing Traversable
	 * @throws CException If data is neither an array nor a Traversable.
	 */
	public function copyFrom($data)
	{
		if(is_array($data) || ($data instanceof Traversable))
		{
			if($this->_c>0)
				$this->clear();
			if($data instanceof CList)
				$data=$data->_d;
			foreach($data as $item)
				$this->add($item);
		}
		else if($data!==null)
			throw new CException(Yii::t('yii','List data must be an array or an object implementing Traversable.'));
	}

	/**
	 * Merges iterable data into the map.
	 * New data will be appended to the end of the existing data.
	 * @param mixed $data the data to be merged with, must be an array or object implementing Traversable
	 * @throws CException If data is neither an array nor an iterator.
	 */
	public function mergeWith($data)
	{
		if(is_array($data) || ($data instanceof Traversable))
		{
			if($data instanceof CList)
				$data=$data->_d;
			foreach($data as $item)
				$this->add($item);
		}
		else if($data!==null)
			throw new CException(Yii::t('yii','List data must be an array or an object implementing Traversable.'));
	}

	/**
	 * Returns whether there is an item at the specified offset.
	 * This method is required by the interface ArrayAccess.
	 * @param integer $offset the offset to check on
	 * @return boolean
	 */
	public function offsetExists($offset)
	{
		return ($offset>=0 && $offset<$this->_c);
	}

	/**
	 * Returns the item at the specified offset.
	 * This method is required by the interface ArrayAccess.
	 * @param integer $offset the offset to retrieve item.
	 * @return mixed the item at the offset
	 * @throws CException if the offset is invalid
	 */
	public function offsetGet($offset)
	{
		return $this->itemAt($offset);
	}

	/**
	 * Sets the item at the specified offset.
	 * This method is required by the interface ArrayAccess.
	 * @param integer $offset the offset to set item
	 * @param mixed $item the item value
	 */
	public function offsetSet($offset,$item)
	{
		if($offset===null || $offset===$this->_c)
			$this->insertAt($this->_c,$item);
		else
		{
			$this->removeAt($offset);
			$this->insertAt($offset,$item);
		}
	}

	/**
	 * Unsets the item at the specified offset.
	 * This method is required by the interface ArrayAccess.
	 * @param integer $offset the offset to unset item
	 */
	public function offsetUnset($offset)
	{
		$this->removeAt($offset);
	}
}