PHP 5.4.33 Released

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();

?>

Exemplul de mai sus va afișa:

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";
}
?>

Exemplul de mai sus va afișa:

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";
}
?>

Exemplul de mai sus va afișa:

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:

Notă:

For more examples of iterators, see the SPL Extension.

Notă:

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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User Contributed Notes 16 notes

up
11
php dot net dot nsp at cvogt dot org
2 years ago
there is still an open bug about using current() etc. with iterators
https://bugs.php.net/bug.php?id=49369
up
4
baldurien at bbnwn dot eu
8 years ago
Beware of how works iterator in PHP if you come from Java!

In Java, iterator works like this :
<?php
interface Iterator<O> {
 
boolean hasNext();
 
O next();
 
void remove();
}
?>
But in php, the interface is this (I kept the generics and type because it's easier to understand)

<?php
interface Iterator<O> {
 
boolean valid();
 
mixed key();
 
O current();
 
void next();
 
void previous();
 
void rewind();
}
?>

1. valid() is more or less the equivalent of hasNext()
2. next() is not the equivalent of java next(). It returns nothing, while Java next() method return the next object, and move to next object in Collections. PHP's next() method will simply move forward.

Here is a sample with an array, first in java, then in php :

<?php
class ArrayIterator<O> implements Iterator<O> {
  private final
O[] array;
  private
int index = 0;

  public
ArrayIterator(O[] array) {
    
this.array = array;
  }
 
  public
boolean hasNext() {
    return
index < array.length;
  } 

  public
O next() {
     if ( !
hasNext())
       throw new
NoSuchElementException('at end of array');
     return array[
index++];
  }

  public
void remove() {
    throw new
UnsupportedOperationException('remove() not supported in array');
  }
}
?>

And here is the same in php (using the appropriate function) :

<?php
/**
* Since the array is not mutable, it should use an internal
* index over the number of elements for the previous/next
* validation.
*/
class ArrayIterator implements Iterator {
  private
$array;
  public function
__construct($array) {
    if ( !
is_array($array))
      throw new
IllegalArgumentException('argument 0 is not an array');
   
$this->array = array;
   
$this->rewind();
  }
  public function
valid() {
    return
current($this->array) !== false;
   
// that's the bad method (should use arrays_keys, + index)
 
}
  public function
key() {
     return
key($this->array);
  }
  public function
current() {
    return
current($this->array);
  }
  public function
next() {
    if (
$this->valid())
      throw new
NoSuchElementException('at end of array');
   
next($this->array);
  }
  public function
previous()  {
   
// fails if current() = first item of array
   
previous($this->array);
  }
  public function
rewind() {
    
reset($this->array);
  }
}
?>

The difference is notable : don't expect next() to return something like in Java, instead use current(). This also means that you have to prefetch your collection to set the current() object. For instance, if you try to make a Directory iterator (like the one provided by PECL), rewind should invoke next() to set the first element and so on. (and the constructor should call rewind())

Also, another difference :

<?php
class ArrayIterable<O> implements Iterable<O> {
  private final
O[] array;

  public
ArrayIterable(O[] array) {
    
this.array = array;
  } 

  public
Iterator<O> iterator() {
     return new
ArrayIterator(array);
  }
}
?>

When using an Iterable, in Java 1.5, you may do such loops :

<?php
for ( String s : new ArrayIterable<String>(new String[] {"a", "b"})) {
  ...
}
?>
Which is the same as :

<?php
Iterator
<String> it = new ArrayIterable<String>(new String[] {"a", "b"});
while (
it.hasNext()) {
 
String s = it.next();
  ...
}
?>
While in PHP it's not the case :
<?php
foreach ( $iterator as $current ) {
  ...
}
?>
Is the same as :

<?php
for ( $iterator->rewind(); $iterator->valid(); $iterator->next()) {
 
$current = $iterator->current();
  ...
}
?>

(I think we may also use IteratorAggregate to do it like with Iterable).

Take that in mind if you come from Java.

I hope this explanation is not too long...
up
1
doctorrock83_at_gmail.com
7 years ago
Please remember that actually the only PHP iterating structure that uses Iterator is foreach().

Any each() or list() applied to an Object implementing iterator will not provide the expected result
up
2
rune at zedeler dot dk
7 years ago
The iterator template from knj at aider dot dk does not yield correct results.
If you do
<?
reset
($a);
next($a);
echo
current($a);
?>
where $a is defined over the suggested template, then the first element will be output, not the second, as expected.
up
2
strrev('ed.relpmeur@ekneos');
9 years ago
Use the SPL ArrayAccess interface to call an object as array:

http://www.php.net/~helly/php/ext/spl/interfaceArrayAccess.html
up
1
wavetrex A(nospam)T gmail DOT com
6 years ago
By reading the posts below I wondered if it really is impossible to make an ArrayAccess implementation really behave like a true array ( by being multi level )

Seems like it's not impossible. Not very preety but usable

<?php

class ArrayAccessImpl implements ArrayAccess {

  private
$data = array();

  public function
offsetUnset($index) {}

  public function
offsetSet($index, $value) {
//    echo ("SET: ".$index."<br>");
   
   
if(isset($data[$index])) {
        unset(
$data[$index]);
    }
   
   
$u = &$this->data[$index];
    if(
is_array($value)) {
       
$u = new ArrayAccessImpl();
        foreach(
$value as $idx=>$e)
           
$u[$idx]=$e;
    } else
       
$u=$value;
  }

  public function
offsetGet($index) {
//    echo ("GET: ".$index."<br>");

   
if(!isset($this->data[$index]))
       
$this->data[$index]=new ArrayAccessImpl();
   
    return
$this->data[$index];
  }

  public function
offsetExists($index) {
//    echo ("EXISTS: ".$index."<br>");
   
   
if(isset($this->data[$index])) {
        if(
$this->data[$index] instanceof ArrayAccessImpl) {
            if(
count($this->data[$index]->data)>0)
                return
true;
            else
                return
false;
        } else
            return
true;
    } else
        return
false;
  }

}

echo
"ArrayAccess implementation that behaves like a multi-level array<hr />";

$data = new ArrayAccessImpl();

$data['string']="Just a simple string";
$data['number']=33;
$data['array']['another_string']="Alpha";
$data['array']['some_object']=new stdClass();
$data['array']['another_array']['x']['y']="LOL @ Whoever said it can't be done !";
$data['blank_array']=array();

echo
"'array' Isset? "; print_r(isset($data['array'])); echo "<hr />";
echo
"<pre>"; print_r($data['array']['non_existent']); echo "</pre>If attempting to read an offset that doesn't exist it returns a blank object! Use isset() to check if it exists!<br>";
echo
"'non_existent' Isset? "; print_r(isset($data['array']['non_existent'])); echo "<br />";
echo
"<pre>"; print_r($data['blank_array']); echo "</pre>A blank array unfortunately returns similar results :(<br />";
echo
"'blank_array' Isset? "; print_r(isset($data['blank_array'])); echo "<hr />";
echo
"<pre>"; print_r($data); echo "</pre> (non_existent remains in the structure. If someone can help to solve this I'll appreciate it)<hr />";

echo
"Display some value that exists: ".$data['array']['another_string'];

?>

(in the two links mentioned below by artur at jedlinski... they say you can't use references, so I didn't used them.
My implementation uses recursive objects)

If anyone finds a better (cleaner) sollution, please e-mail me.
Thanks,
Wave.
up
0
artur at jedlinski dot pl
7 years ago
One should be aware that ArrayAccess functionality described by "just_somedood at yahoo dot com" below is currently broken and thus it's pretty unusable.

Read following links to find more:
http://bugs.php.net/bug.php?id=34783
http://bugs.php.net/bug.php?id=32983
up
0
chad 0x40 herballure 0x2e com
8 years ago
The example code given for valid() will break if the array contains a FALSE value. This code prints out a single "bool(true)" and exits the loop when it gets to the FALSE:

<?php
$A
= array(TRUE, FALSE, TRUE, TRUE);
while(
current($A) !== FALSE) {
 
var_dump(current($A));
 
next($A);
}
?>

Instead, the key() function should be used, since it returns NULL only at the end of the array. This code displays all four elements and then exits:

<?php
$A
= array(TRUE, FALSE, TRUE, TRUE);
while(!
is_null(key($A))) {
 
var_dump(current($A));
 
next($A);
}
?>
up
0
markushe at web dot de
9 years ago
Just something i noticed:
It seems, that when you are implementing the interface Iterator, yout method key() has to return a string or integer.

I was trying to return a object an got this error:
Illegal type returned from MyClass::key()
up
0
just_somedood at yahoo dot com
9 years ago
To clarify on php at moechofe's post, you CAN use the SPL to overide the array operator for a class.  This, with the new features of object, and autoloading (among a buch of other things) has me completely sold on PHP5.  You can also find this information on the SPL portion of the manual, but I'll post it here as well so it isn't passed up.  The below Collection class will let you use the class as an array, while also using the foreach iterator:

<?php

class Collection implements ArrayAccess,IteratorAggregate
{
    public
$objectArray = Array();
   
//**these are the required iterator functions   
   
function offsetExists($offset)
    {         
        if(isset(
$this->objectArray[$offset]))  return TRUE;
        else return
FALSE;         
    }   
   
    function &
offsetGet($offset)
    {  
        if (
$this->offsetExists($offset))  return $this->objectArray[$offset];
        else return (
false);
    }
   
    function
offsetSet($offset, $value)
    {         
        if (
$offset$this->objectArray[$offset] = $value;
        else 
$this->objectArray[] = $value;
    }
   
    function
offsetUnset($offset)
    {
        unset (
$this->objectArray[$offset]);
    }
   
    function &
getIterator()
    {
        return new
ArrayIterator($this->objectArray);
    }
   
//**end required iterator functions

   
public function doSomething()
    {
        echo
"I'm doing something";
    }
}

?>

I LOVE the new SPL stuff in PHP!  An example of usage is below:

<?php
class Contact
{
    protected
$name = NULL;

    public function
set_name($name)
    {
       
$this->name = $name;
    }
   
    public function
get_name()
    {
        return (
$this->name);
    }
}

$bob = new Collection();
$bob->doSomething();
$bob[] = new Contact();
$bob[5] = new Contact();
$bob[0]->set_name("Superman");
$bob[5]->set_name("a name of a guy");

foreach (
$bob as $aContact)
{
     echo
$aContact->get_name() . "\r\n";
}
?>

Would work just fine.  This makes code so much simpler and easy to follow, it's great.  This is exactly the direction I had hoped PHP5 was going!
up
0
elias at need dot spam
9 years ago
The MyIterator::valid() method above ist bad, because it
breaks on entries with 0 or empty strings, use key() instead:

<?php
public function valid()
{
    return !
is_null(key($this->var));
}
?>

read about current() drawbacks:
http://php.net/current
up
0
phpnet at nicecupofteaandasitdown dot com
9 years ago
You should be prepared for your iterator's current method to be called before its next method is ever called. This certainly happens in a foreach loop. If your means of finding the next item is expensive you might want to use something like this

private $item;
       
function next() {
    $this->item = &$this->getNextItem();
    return $this->item;
}
   
public function current() {
     if(!isset($this->item)) $this->next();
    return $this->item;
}
up
-1
hlegius at gmail dot com
5 years ago
Iterator interface usign key() next() rewind() is MORE slow than extends ArrayIterator with ArrayIterator::next(), ArrayIterator::rewind(), etc.,
up
-1
PrzemekG_ at poczta dot onet dot pl
9 years ago
If you want to do someting like this:
<?php
foreach($MyObject as $key => &$value)
  
$value = 'new '.$value;
?>
you must return values by reference in your iterator object:
<?php
class MyObject implements Iterator
{
/* ...... other iterator functions ...... */
/* return by reference */
public function &current()
{
   return
$something;
}
?>

This won't change values:
<?php
foreach($MyObject as $key => $value)
  
$value = 'new '.$value;
?>

This will change values:
<?php
foreach($MyObject as $key => &$value)
  
$value = 'new '.$value;
?>

I think this should be written somewhere in the documentations, but I couldn't find it.
up
-1
knj at aider dot dk
9 years ago
if you in a string define classes that implements IteratorAggregate.
you cant use the default;
<?
...
public function
getIterator() {
       return new
MyIterator(\\$this-><What ever>);
}
..
?>
at least not if you want to use eval(<The string>).
You have to use:
<?
...
public function
getIterator() {
      \\
$arrayObj=new ArrayObject(\\$this-><What ever>);
      return \\
$arrayObj->getIterator();
}
...
?>
up
-4
jille at hexon dot cx
2 years ago
Please note that if you implement your iterator this way instead of with an IteratorAggregate you can not nest foreach-loops. This is because when the inner-loop is done the cursor is beyond the last element, then the outer-loop asks for the next element and finds the cursor beyond the last element as the innter-loop left it there.

<?php
// Wont work!
foreach($collection as $a) {
  foreach(
$collection as $b) {
   
var_dump($a->someFunc($b));
  }
}
?>
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