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 sektionen med navn foreach i Kapitel 11 statement. By default, all public properties will be used for the iteration.

Eksempel 14-14. Simple Object Iteration

<?php

class MyClass {
  
public $var1 = 'value 1';
  
public $var2 = 'value 2';
  
public $var3 = 'value 3';

  
protected $protected = 'protected';
  
private   $private   = 'private';

}

$class = new MyClass();

foreach(
$class as $key => $value) {
  print
"$key => $value\n";
}

Will output:

var1 => value 1
var2 => value 2
var3 => value 3

As the output shows, the sektionen med navn foreach i Kapitel 11 iterated through each public variable that is defined. To take it a step further you can implement one of PHP 5's internal sektionen med navn Object Interfaces named Iterator. This allows the object to decide what and how the object will be iterated.

Eksempel 14-15. Object Iteration implenting 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";
}

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.

Eksempel 14-16. Object Iteration implenting 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";
}

?>
</pre>

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: