PHP基础之类和对象14——遍历对象

PHP 5 提供了一种定义对象的方法使其可以通过单元列表来遍历，例如用 foreach 语句。默认情况下，所有可见属性都将被用于遍历。
Example #1 简单的对象遍历

class MyClass
{
    public $var1 = 1;
    public $var2 = 2;
    public $var3 = 3;
    protected $protected = 'protected var';

    private $private = 'private var';

    function iterateVisible(){
        echo "MyClass::iterateVisible:<br>";
        foreach($this as $key => $value){
            print "$key=>$value<br>";
        }
    }
} 

$class = new MyClass();

foreach($class as $key => $value){
    print "$key => $value<br>";
}

echo "<br>";
$class->iterateVisible();

输出结果：
var1 => 1
var2 => 2
var3 => 3
MyClass::iterateVisible:
var1=>1
var2=>2
var3=>3
protected=>protected var
private=>private var
如上所示，foreach 遍历了所有其能够访问的可见属性。
更进一步，可以实现 Iterator接口。可以让对象自行决定如何遍历以及每次遍历时那些值可用。

class MyIterator implements Iterator{
    private $var = array();
    public function __construct($array)
    {
        if(is_array($array)){
            $this->var = $array;
        }
    }

    public function rewind(){
        echo "rewinding<br>";
        reset($this->var);
    }

    public function current(){
        $var = current($this->var);
        echo "current:$var<br>";
        return $var;
    }

    public function key(){
        $var = key($this->var);
        echo "key:$var<br>";
        return $var;
    }

    public function next(){
        $var = next($this->var);
        echo "next:$var<br>";
        return $var;
    }

    public function valid(){
        $var = $this->current()!==false;
        echo "valid:$var<br>";
        return $var;
    }
}

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

foreach($it as $a => $b){
    print "$a:$b<br>";
}

输出结果：
rewinding
current:1
valid:1
current:1
key:0
0:1
next:2
current:2
valid:1
current:2
key:1
1:2
next:3
current:3
valid:1
current:3
key:2
2:3
next:
current:
valid:
可以用 IteratorAggregate接口以替代实现所有的 Iterator 方法。IteratorAggregate 只需要实现一个方法 IteratorAggregate::getIterator()，其应返回一个实现了 Iterator 的类的实例。
Example #3 通过实现 IteratorAggregate 来遍历对象

include_once('class2.php');

class MyCollection implements IteratorAggregate
{
    private $items = array();
    private $count = 0;

    public function getIterator(){
       return new MyIterator($this->items);
    }

    public function add($value){
        $this->items[$this->count++] = $value;
    }
}

$coll = new MyCollection();
$coll -> add('1');
$coll -> add('2');
$coll -> add('3');

foreach($coll as $k => $v){
    echo "key/value:[$k->$v]<br><br>";
}

输出结果：
rewinding
current:1
valid:1
current:1
key:0
key/value:[0->1]


next:2
current:2
valid:1
current:2
key:1
key/value:[1->2]


next:3
current:3
valid:1
current:3
key:2
key/value:[2->3]

next:
current:
valid: