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

    function rewind() {
        var_dump(__METHOD__);
        $this->position = 0;
    }

    function current() {
        var_dump(__METHOD__);
        return $this->array[$this->position];
    }

    function key() {
        var_dump(__METHOD__);
        return $this->position;
    }

    function next() {
        var_dump(__METHOD__);
        ++$this->position;
    }

    function valid() {
        var_dump(__METHOD__);
        return isset($this->array[$this->position]);
    }
}

$it = new myIterator;

foreach($it as $key => $value) {
 echo '輸出鍵值：';
    var_dump($key, $value);
 //echo $key;
    echo "\n";
}

string(16) "myIterator::next"
string(17) "myIterator::valid"
string(19) "myIterator::current"
string(15) "myIterator::key"
輸出鍵值：int(1)
string(14) "second_element"

string(16) "myIterator::next"
string(17) "myIterator::valid"
string(19) "myIterator::current"
string(15) "myIterator::key"
輸出鍵值：int(2)
string(12) "last_element"

string(16) "myIterator::next"
string(17) "myIterator::valid"

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

     public function rewind() {
         echo "倒回第一個(gè)元素\n";
        reset($this->var);
     }

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

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

     public function next() {
        $var = next($this->var);
         echo "移向下一個(gè)元素: $var\n";
         return $var;
     }

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

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

foreach ($it as $k => $v) {
     print "此時(shí)鍵值對(duì) -- key $k: value $v\n\n";
}

移向下一個(gè)元素: 2
當(dāng)前元素: 2
檢查有效性: 1
當(dāng)前元素: 2
當(dāng)前元素的鍵: 1
此時(shí)鍵值對(duì) -- key 1: value 2

移向下一個(gè)元素: 3
當(dāng)前元素: 3
檢查有效性: 1
當(dāng)前元素: 3
當(dāng)前元素的鍵: 2
此時(shí)鍵值對(duì) -- key 2: value 3

移向下一個(gè)元素:
當(dāng)前元素:
檢查有效性: