php traverse objects

PHP 5 provides a way to define objects so that they can be traversed through a list of cells, such as using the foreach statement. By default, all visible properties will be used for traversal.

Example #1 Simple object traversal

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();

Output result:

var1 => 1

var2 => 2

var3 => 3

MyClass::iterateVisible:

var1=>1

var2=>2

var3=>3

protected=>protected var

private=>private var

As shown above, foreach traverses all the visible properties it can access.

Going a step further, you can implement the Iterator interface. You can let the object decide for itself how to traverse and which values ​​are available each time it is traversed.

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>";
}

Output result:

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:

You can use the IteratorAggregate interface instead of implementing all Iterator methods. IteratorAggregate only needs to implement one method, IteratorAggregate::getIterator(), which should return an instance of the class that implements Iterator.

Example #3 Traverse objects by implementing IteratorAggregate

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>";
}

Output result:

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: