PHP遍歷接口Iterator詳解

從手冊中查到的解釋是：

Iterator extends Traversable {
/* Methods */
abstract public mixed current ( void )
abstract public scalar key ( void )
abstract public void next ( void )
abstract public void rewind ( void )
abstract public boolean valid ( void )
}

當一個實現了Iterator接口的對象，被foreach遍歷時，會自動調用這些方法。調用的循序是：
rewind() -> valid() -> current() -> key() -> next()

下面來看一下簡單的代碼：

class myIterator implements Iterator {  
    private $position = 0;  
    private $array = array(  
        "firstelement",  
        "secondelement",  
        "lastelement",  
    );    
  
    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 => $value) {  
    var_dump($key, $value);  
    echo '---------------------------'."\n";
}

以上會輸出：

/Users/thanatos/Web/study/blean.php:15:string 'myIterator::rewind' (length=18)
/Users/thanatos/Web/study/blean.php:35:string 'myIterator::valid' (length=17)
/Users/thanatos/Web/study/blean.php:20:string 'myIterator::current' (length=19)
/Users/thanatos/Web/study/blean.php:25:string 'myIterator::key' (length=15)
/Users/thanatos/Web/study/blean.php:43:int 0
/Users/thanatos/Web/study/blean.php:43:string 'firstelement' (length=12)
---------------------------
/Users/thanatos/Web/study/blean.php:30:string 'myIterator::next' (length=16)
/Users/thanatos/Web/study/blean.php:35:string 'myIterator::valid' (length=17)
/Users/thanatos/Web/study/blean.php:20:string 'myIterator::current' (length=19)
/Users/thanatos/Web/study/blean.php:25:string 'myIterator::key' (length=15)
/Users/thanatos/Web/study/blean.php:43:int 1
/Users/thanatos/Web/study/blean.php:43:string 'secondelement' (length=13)
---------------------------
/Users/thanatos/Web/study/blean.php:30:string 'myIterator::next' (length=16)
/Users/thanatos/Web/study/blean.php:35:string 'myIterator::valid' (length=17)
/Users/thanatos/Web/study/blean.php:20:string 'myIterator::current' (length=19)
/Users/thanatos/Web/study/blean.php:25:string 'myIterator::key' (length=15)
/Users/thanatos/Web/study/blean.php:43:int 2
/Users/thanatos/Web/study/blean.php:43:string 'lastelement' (length=11)
---------------------------
/Users/thanatos/Web/study/blean.php:30:string 'myIterator::next' (length=16)
/Users/thanatos/Web/study/blean.php:35:string 'myIterator::valid' (length=17)