PHP foreach遍历多维数组实现方式

$test_arr = array(1,2,3,array(4,'aa'=>5,6,array(7,'bb'=>8),9,10),11,12);
 $arrayiter = new RecursiveArrayIterator($test_arr);
 $iteriter = new RecursiveIteratorIterator($arrayiter);
 //直接打印即可按照横向顺序打印出来
 foreach ($iteriter as $key => $val){
   echo $key.'=>'.$val;
 }
 //结果
 /*
   0=>1
   1=>2
   2=>3
   0=>4
   aa=>5
   2=>6
   0=>7
   bb=>8
   4=>9
   5=>10
   4=>11
   5=>12
*/

class foreachPrintfArr implements Iterator {
    //当前数组作用域
    private $_items;
    private $_old_items;
    //保存每次执行数组环境栈
    private $_stack = array();
 
    public function __construct($data=array()){
      $this->_items = $data;
    }
 
    private function _isset(){
      $val = current($this->_items);
 
      if (empty($this->_stack) && !$val) {
        return false;
      } else {
        return true;
      } 
    }
 
    public function current() {
      $this->_old_items = null;
      $val = current($this->_items);
 
      //如果是数组则保存当前执行环境，然后切换到新的数组执行环境
      if (is_array($val)){
        array_push($this->_stack,$this->_items);
        $this->_items = $val;
        return $this->current();
      }
 
      //判断当前执行完成后是否需要切回上次执行环境
      //(1) 如果存在跳出继续执行
      //(2) 如果不存在且环境栈为空，则表示当前执行到最后一个元素
      //(3) 如果当前数组环境下一个元素不存在,则保存一下当前执行数组环境 $this->_old_items = $this->_items;
      //然后切换上次执行环境 $this->_items = array_pop($this->_stack) 继续循环, 直到当前数组环境下一个
      //元素不为空为止
      while (1) {
        if (next($this->_items)) { 
          prev($this->_items); break;
        } elseif (empty($this->_stack)) {
          end($this->_items); break;
        } else {
          end($this->_items);
          if (!$this->_old_items)
            $this->_old_items = $this->_items;
          $this->_items = array_pop($this->_stack);
        }
      }
 
      return $val;
    }
 
    public function next() {
      next($this->_items); 
    }
 
    public function key() {
      // 由于 key() 函数执行在 current() 函数之后
      // 所以在 current() 函数切换执行环境 , 会导致切换之前的执行环境最后一个 key
      // 变成切换之后的key , 所以 $this->_old_items 保存一下切换之前的执行环境
      // 防止key打印出错
      return $this->_old_items ? key($this->_old_items) : key($this->_items);
    }
 
    public function rewind() {
      reset($this->_items);
    }
 
    public function valid() {                                      
      return $this->_isset();
    }
  }

$test_arr = array(1,2,3,array(4,'aa'=>5,6,array(7,'bb'=>8),9,10),11,12);
$iteriter = new foreachPrintfArr($test_arr);
foreach ($iteriter as $key => $val){
  echo $key.'=>'.$val;
}
//结果：
/*
0=>1
1=>2
2=>3
0=>4
aa=>5
2=>6
0=>7
bb=>8
4=>9
5=>10
4=>11
5=>12
*/