Object Iteration

PHP 5 provides a way for objects to be defined so it is possible to iterate through a list of items, with, for example a foreach statement. By default, all visible properties will be used for the iteration.

Example 19-20. Simple Object Iteration


<?php

class MyClass

{

    public $var1 = 'value 1';

    public $var2 = 'value 2';

    public $var3 = 'value 3';



    protected $protected = 'protected var';

    private   $private   = 'private var';



    function iterateVisible() {

       echo "MyClass::iterateVisible:\n";

       foreach($this as $key => $value) {

           print "$key => $value\n";

       }

    }

}



$class = new MyClass();



foreach($class as $key => $value) {

    print "$key => $value\n";

}

echo "\n";





$class->iterateVisible();



?>

The above example will output:


var1 => value 1

var2 => value 2

var3 => value 3



MyClass::iterateVisible:

var1 => value 1

var2 => value 2

var3 => value 3

protected => protected var

private => private var

As the output shows, the foreach iterated through all visible variables that can be accessed. To take it a step further you can implement one of PHP 5's internal interface named Iterator. This allows the object to decide what and how the object will be iterated.

Example 19-21. Object Iteration implementing Iterator


<?php

class MyIterator implements Iterator

{

    private $var = array();



    public function __construct($array)

    {

        if (is_array($array)) {

            $this->var = $array;

        }

    }



    public function rewind() {

        echo "rewinding\n";

        reset($this->var);

    }



    public function current() {

        $var = current($this->var);

        echo "current: $var\n";

        return $var;

    }



    public function key() {

        $var = key($this->var);

        echo "key: $var\n";

        return $var;

    }



    public function next() {

        $var = next($this->var);

        echo "next: $var\n";

        return $var;

    }



    public function valid() {

        $var = $this->current() !== false;

        echo "valid: {$var}\n";

        return $var;

    }

}



$values = array(1,2,3);

$it = new MyIterator($values);



foreach ($it as $a => $b) {

    print "$a: $b\n";

}

?>

The above example will output:


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 also define your class so that it doesn't have to define all the Iterator functions by simply implementing the PHP 5 IteratorAggregate interface.

Example 19-22. Object Iteration implementing IteratorAggregate


<?php

class MyCollection implements IteratorAggregate

{

    private $items = array();

    private $count = 0;



    // Required definition of interface IteratorAggregate

    public function getIterator() {

        return new MyIterator($this->items);

    }



    public function add($value) {

        $this->items[$this->count++] = $value;

    }

}



$coll = new MyCollection();

$coll->add('value 1');

$coll->add('value 2');

$coll->add('value 3');



foreach ($coll as $key => $val) {

    echo "key/value: [$key -> $val]\n\n";

}

?>

The above example will output:


rewinding

current: value 1

valid: 1

current: value 1

key: 0

key/value: [0 -> value 1]



next: value 2

current: value 2

valid: 1

current: value 2

key: 1

key/value: [1 -> value 2]



next: value 3

current: value 3

valid: 1

current: value 3

key: 2

key/value: [2 -> value 3]



next:

current:

valid:

Note: For more examples of iterators, see the SPL Extension.

User Contributed Notes
Object Iteration

elias at need dot spam
10-Apr-2005 06:15


The MyIterator::valid() method above ist bad, because it

breaks on entries with 0 or empty strings, use key() instead:



<?php

public function valid()

{

    return ! is_null(key($this->var));

}

?>



read about current() drawbacks:

http://php.net/current

strrev('ed.relpmeur@ekneos');
01-Mar-2005 05:25


Use the SPL ArrayAccess interface to call an object as array:



http://www.php.net/~helly/php/ext/spl/interfaceArrayAccess.html

phpnet at nicecupofteaandasitdown dot com
22-Feb-2005 11:09


You should be prepared for your iterator's current method to be called before its next method is ever called. This certainly happens in a foreach loop. If your means of finding the next item is expensive you might want to use something like this



private $item;

        

function next() {

    $this->item = &$this->getNextItem();

    return $this->item;

}

    

public function current() {

     if(!isset($this->item)) $this->next();

    return $this->item;

}

knj at aider dot dk
18-Dec-2004 10:19


if you in a string define classes that implements IteratorAggregate.

you cant use the default;

<?

...

public function getIterator() {

       return new MyIterator($this-><What ever>);

}

..

?>

at least not if you want to use eval(<The string>).

You have to use:

<?

...

public function getIterator() {

      $arrayObj=new ArrayObject($this-><What ever>);

      return $arrayObj->getIterator();

}

...

?>

php at moechofe dot com
13-Dec-2004 06:27


<?php



class MyIterator implements Iterator {



  private $var = array();



  public function __construct() {

    $this->var = array( 1,2,3,4 ); }



  public function rewind() { reset($this->var); }

  public function current() { return current($this->var); }

  public function key() { return key($this->var); }

  public function next() { return next($this->var); }

  public function valid() { return $this->current() !== false; }



  }



$it = new MyIterator();



// dont work :(

echo $it[0];



?>