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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 10.22. 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 10.23. 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 10.24. 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.