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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 #1 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 of the visible properties that could be accessed.

To take it a step further, the Iterator interface may be implemented. This allows the object to dictate how it will be iterated and what values will be available on each iteration.

Example #2 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()
    {
        
$key key($this->var);
        
$var = ($key !== NULL && $key !== 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
valid: 1
current: 1
key: 0
0: 1
next: 2
valid: 1
current: 2
key: 1
1: 2
next: 3
valid: 1
current: 3
key: 2
2: 3
next:
valid: 

The IteratorAggregate interface can be used as an alternative to implementing all of the Iterator methods. IteratorAggregate only requires the implementation of a single method, IteratorAggregate::getIterator, which should return an instance of a class implementing Iterator.

Example #3 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.

Note:

Users of PHP 5.5 and later may also want to investigate generators, which provide an alternative way of defining iterators.

PHP Manual