php预定义接口中迭代的执行流程

<?php 

class  myIterator  implements  Iterator {
    private  $position  =  0 ;
    private  $array  = array(
         "firstelement" ,
         "secondelement" ,
         "lastelement" ,
    );  

    public function  __construct () {
         $this -> position  =  0 ;
    }

      //第一步
    function  rewind () {
        echo ‘第一轮遍历时执行此方法 以后都不执行‘;
         var_dump ( __METHOD__ );
         $this -> position  =  0 ;
    }

   //第二步
    function  valid () {
        echo ‘valid‘;
        var_dump ( __METHOD__ );
        return isset( $this -> array [ $this -> position ]);
    }

    //第三步
    function  current () {
        echo ‘current方法， 如果valid()方法返回false，此处停止，不往下执行‘;
         var_dump ( __METHOD__ );
        return  $this -> array [ $this -> position ];
    }

     //第四步
    function  key () {
        echo ‘key‘;
         var_dump ( __METHOD__ );
        return  $this -> position ;
    }

    function  next () {
        echo ‘第 ‘ . $this -> position . ‘轮遍历时执行此方法‘;
         var_dump ( __METHOD__ );
        ++ $this -> position ;
    }

}

$it  = new  myIterator() ;

foreach( $it  as  $key  =>  $value ) {
    print_r($key);
    echo "==============>>>>>>>>>>>>>";
    print_r($value);
    echo "\r\n \r\n";
}