PHP模拟asp.net的StringBuilder类实现方法

/******************************************** 
 * 
 * 函数名：StringBuilder 
 * 作 用：构造PHP下的StringBuilder类 
 * 
 ********************************************/
class StringBuilder 
{ 
  const LINE="<br/>"; 
  protected $list= array(''); 
  public function __construct( $str=NULL) 
  { 
    array_push($this->list,$str); 
  } 
  public function Append($str) 
  { 
    array_push($this->list,$str); 
    return $this; 
  } 
  public function AppendLine($str) 
  { 
    array_push($this->list,$str.self::LINE); 
    return $this; 
  } 
  public function AppendFormat( $str,mixed $args) 
  { 
    array_push($this->list, sprintf($str,$args)); 
    return $this; 
  } 
  public function ToString() 
  { 
    return implode("",$this->list); 
  } 
  public function __destruct() 
  { 
    unset($this->list); 
  } 
}