看看PHP迭代器的内部执行过程

 1 class myIterator implements Iterator {
 2     private $position = 0;
 3     private $array = array(
 4         "first_element",
 5         "second_element",
 6         "last_element",
 7     );  
 8 
 9     public function __construct() {
10         $this->position = 0;
11     }
12 
13     function rewind() {
14         var_dump(__METHOD__);
15         $this->position = 0;
16     }
17 
18     function current() {
19         var_dump(__METHOD__);
20         return $this->array[$this->position];
21     }
22 
23     function key() {
24         var_dump(__METHOD__);
25         return $this->position;
26     }
27 
28     function next() {
29         var_dump(__METHOD__);
30         ++$this->position;
31     }
32 
33     function valid() {
34         var_dump(__METHOD__);
35         return isset($this->array[$this->position]);
36     }
37 }
38 
39 $it = new myIterator;
40 
41 foreach($it as $key => $value) {
42     echo ‘输出键值：‘;
43     var_dump($key, $value);
44     //echo $key;
45     echo "\n";
46 }

/**
* 
*/
class MyIterator implements Iterator
{
     private $var = array();

     public function __construct($array)
     {
         if (is_array($array)) {
            $this->var = $array;
         }
     }

     public function rewind() {
         echo "倒回第一个元素\n";
        reset($this->var);
     }

     public function current() {
        $var = current($this->var);
         echo "当前元素: $var\n";
         return $var;
     }

     public function key() {
        $var = key($this->var);
         echo "当前元素的键: $var\n";
         return $var;
     }

     public function next() {
        $var = next($this->var);
         echo "移向下一个元素: $var\n";
         return $var;
     }

     public function valid() {
        $var = $this->current() !== false;
         echo "检查有效性: {$var}\n";
         return $var;
     }
}

$values = array(1,2,3);
$it = new MyIterator($values);

foreach ($it as $k => $v) {
     print "此时键值对 -- key $k: value $v\n\n";
}