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 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 #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 () {
$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 #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.
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