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.
<?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.
<?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.
<?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:
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