Object Iteration

Examples:

Simple 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.

<?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

Object Iteration implementing Iterator

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:

Object Iteration implementing IteratorAggregate

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:

Links:

http://php.net/manual/en/language.oop5.iterations.php

doc_php

2025-01-10 15:47:30

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