迭代器或类的接口。

Iterator extends Traversable  
{  
    //返回当前索引游标指向的元素  
    abstract public mixed current(void)  
    //返回当前索引游标指向的元素的键名  
    abstract public scalar key(void)  
    //移动当前索引游标指向下一元素  
    abstract public void next(void)  
    //重置索引游标的指向第一个元素  
    abstract public void rewind(void)  
    //判断当前索引游标指向的是否是一个元素，常常在调用 rewind()或 next()使用  
    abstract public boolean valid(void)  
} 

scalar 标准变量 整型、字符串、浮点型等

$a="hello word";
$obj=(object)$a;
echo $obj->scalar;
//输出 "hello word"

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 => $value) {
    echo "{$key}|{$value}";
    echo "\n";    
}

输出结果：

0|firstelement
1|secondelement
2|lastelement

Traversable 预定义接口

Traversable {

}

作用：检测一个类是否可以使用 foreach 进行遍历的接口。
php代码中不能用。只有内部的PHP类（用C写的类）才可以直接实现Traversable接口

IteratorAggregate
预定义接口（对Iterator的委托）

class myDataArray implements IteratorAggregate {
    private $_d = array('a','b','c','d');

    public function __construct() {
        $this->_d[] =   "last property";
    }

    public function getIterator() {
        return new ArrayIterator($this->_d);
    }
}

$obj = new myDataArray;

foreach($obj as $key => $value) {
    var_dump($key, $value);
    echo "\n";
}

ArrayAccess

PHP的ArrayAccess接口 像数组一样来访问你的PHP对象

class Test implements ArrayAccess {
        
    private $elements;
    
    public function offsetExists($offset){
        return isset($this->elements[$offset]);
    }
    
    public function offsetSet($offset, $value){
        $this->elements[$offset] = $value;
    }
    
    public function offsetGet($offset){
        return $this->elements[$offset];
    }
    
    public function offsetUnset($offset){
        unset($this->elements[$offset]);
    }
}

$test = new Test();
$test['test'] = 'test';//自动调用offsetSet
if(isset($test['test']))//自动调用offsetExists
{
    echo $test['test'];//自动调用offsetGet
    echo '<br />';
    unset($test['test']);//自动调用offsetUnset
    var_dump($test['test']);
}

Lararel中常常使用比如$this['config']

SeekableIterator 预定义接口

对接口Iterator的扩展
在接口中可以 seek

SeekableIterator extends Iterator {
/* 方法 */
abstract public void seek ( int $position )
/* 继承的方法 */
abstract public mixed Iterator::current ( void )
abstract public scalar Iterator::key ( void )
abstract public void Iterator::next ( void )
abstract public void Iterator::rewind ( void )
abstract public boolean Iterator::valid ( void )

Serializable

扩展接口，对类序列化就是对类内对应方法数据序列反序列化

class obj implements Serializable {
    private $data;
    public function __construct() {
        $this->data = ["My private data"];
    }
    public function serialize() {
        return serialize($this->data);
    }
    public function unserialize($data) {
        $this->data = unserialize($data);
    }
    public function getData() {
        return $this->data;
    }
}

$obj = new obj;
$ser = serialize($obj);

$newobj = unserialize($ser);

var_dump($newobj->getData());

Countable

能够对对象实现count操作

class  Basket implements Countable{
    private $fruits =array('apple','banna','pear','orange','watermelon');
    public function count(){
        return count($this->fruits);
    }
}
$basket = new Basket();
var_dump(count($basket));