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.
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Document created the 30/01/2003, last modified the 26/10/2018
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References
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