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<?php
/**
* This file contains classes implementing the stack feature.
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @link http://www.yiiframework.com/
* @copyright Copyright &copy; 2008-2009 Yii Software LLC
* @license http://www.yiiframework.com/license/
*/

/**
* CStack implements a stack.
*
* The typical stack operations are implemented, which include
* {@link push()}, {@link pop()} and {@link peek()}. In addition,
* {@link contains()} can be used to check if an item is contained
* in the stack. To obtain the number of the items in the stack,
* check the {@link getCount Count} property.
*
* Items in the stack may be traversed using foreach as follows,
* <pre>
* foreach($stack as $item) ...
* </pre>
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @version $Id$
* @package system.collections
* @since 1.0
*/
class CStack extends CComponent implements IteratorAggregate,Countable
{
/**
* internal data storage
* @var array
*/
private $_d=array();
/**
* number of items
* @var integer
*/
private $_c=0;

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

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

/**
* Copies iterable data into the stack.
* Note, existing data in the list will be cleared first.
* @param mixed 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))
{
$this->clear();
foreach($data as $item)
{
$this->_d[]=$item;
++$this->_c;
}
}
else if($data!==null)
throw new CException(Yii::t('yii','Stack data must be an array or an object implementing Traversable.'));
}

/**
* Removes all items in the stack.
*/
public function clear()
{
$this->_c=0;
$this->_d=array();
}

/**
* @param mixed the item
* @return boolean whether the stack contains the item
*/
public function contains($item)
{
return array_search($item,$this->_d,true)!==false;
}

/**
* Returns the item at the top of the stack.
* Unlike {@link pop()}, this method does not remove the item from the stack.
* @return mixed item at the top of the stack
* @throws CException if the stack is empty
*/
public function peek()
{
if($this->_c)
return $this->_d[$this->_c-1];
else
throw new CException(Yii::t('yii','The stack is empty.'));
}

/**
* Pops up the item at the top of the stack.
* @return mixed the item at the top of the stack
* @throws CException if the stack is empty
*/
public function pop()
{
if($this->_c)
{
--$this->_c;
return array_pop($this->_d);
}
else
throw new CException(Yii::t('yii','The stack is empty.'));
}

/**
* Pushes an item into the stack.
* @param mixed the item to be pushed into the stack
*/
public function push($item)
{
++$this->_c;
array_push($this->_d,$item);
}

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

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

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