Overloading
This is what seems to work for checking isFirst() and isLast() on a class implementing the Iterator interface - without destroying the internal array pointer:
<?php
// Let $this->_elements be your internal array with
// array("one", "two", "three")
public function isFirst()
{
$hasPrevious = prev($this->_elements);
// now undo
if ($hasPrevious) {
next($this->_elements);
} else {
reset($this->_elements);
}
return !$hasPrevious;
}
public function isLast()
{
$hasNext = next($this->_elements);
// now undo
if ($hasNext) {
prev($this->_elements);
} else {
end($this->_elements);
}
return !$hasNext;
}
// usage
foreach ($myInterator as $value) {
echo $value;
if ($myInterator->isFirst()) {
echo " (first)";
}
if ($myInterator->isLast()) {
echo " (last)";
}
echo " - value is still the same: ", $value, "<br />";
}
?>
output:
one (first) - value is still the same: one
two - value is still the same: two
three (last) - value is still the same: three
This can be helpfull for designing CSS elements where the first or last element must have a different padding/margin than the others.
Objektiteration
PHP 5 bietet eine Möglichkeit, Objekte so zu definieren, dass es möglich ist, eine Liste von Elementen zu durchlaufen, z.B. mit dem foreach Schlüsselwort. Standardmäßig werden alle sichtbaren Eigenschaften für die Iteration benutzt.
Beispiel #1 Einfache Objektiteration
<?php
class MyClass
{
public $var1 = 'Wert 1';
public $var2 = 'Wert 2';
public $var3 = 'Wert 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();
?>
Das oben gezeigte Beispiel erzeugt folgende Ausgabe:
var1 => Wert 1 var2 => Wert 2 var3 => Wert 3 MyClass::iterateVisible: var1 => Wert 1 var2 => Wert 2 var3 => Wert 3 protected => protected var private => private var
Wie die Ausgabe zeigt, lief das foreach über alle sichtbaren Variablen, auf die zugegriffen werden kann. Um es einen Schritt weiter zu treiben, kann man eines der PHP 5 internen Interfaces, nämlich Iterator, implementieren. Das erlaubt dem Objekt zu entscheiden was und wie das Objekt iteriert wird.
Beispiel #2 Objektiteration mit implementiertem Iterator
<?php
class MyIterator implements Iterator
{
private $var = array();
public function __construct($array)
{
if (is_array($array)) {
$this->var = $array;
}
}
public function rewind() {
echo "zurückspulen\n";
reset($this->var);
}
public function current() {
$var = current($this->var);
echo "aktuell: $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 "nächstes: $var\n";
return $var;
}
public function valid() {
$var = $this->current() !== false;
echo "gültig: {$var}\n";
return $var;
}
}
$values = array(1,2,3);
$it = new MyIterator($values);
foreach ($it as $a => $b) {
print "$a: $b\n";
}
?>
Das oben gezeigte Beispiel erzeugt folgende Ausgabe:
zurückspulen aktuell: 1 gültig: 1 aktuell: 1 key: 0 0: 1 nächstes: 2 aktuell: 2 gültig: 1 aktuell: 2 key: 1 1: 2 nächstes: 3 aktuell: 3 gültig: 1 aktuell: 3 key: 2 2: 3 nächstes: aktuell: gültig:
Man kann eine Klasse ebenfalls so definieren, dass diese nicht alle Funktionen von Iterator definieren muss, indem man einfach das PHP 5 IteratorAggregate Interface implementiert.
Beispiel #3 Objektiteration mit implementiertem IteratorAggregate
<?php
class MyCollection implements IteratorAggregate
{
private $items = array();
private $count = 0;
// benötigte Funktion des IteratorAggregate Interface
public function getIterator() {
return new MyIterator($this->items);
}
public function add($value) {
$this->items[$this->count++] = $value;
}
}
$coll = new MyCollection();
$coll->add('Wert 1');
$coll->add('Wert 2');
$coll->add('Wert 3');
foreach ($coll as $key => $val) {
echo "key/value: [$key -> $val]\n\n";
}
?>
Das oben gezeigte Beispiel erzeugt folgende Ausgabe:
zurückspulen aktuell: Wert 1 gültig: 1 aktuell: Wert 1 key: 0 key/value: [0 -> Wert 1] nächstes: Wert 2 aktuell: Wert 2 gültig: 1 aktuell: Wert 2 key: 1 key/value: [1 -> Wert 2] nächstes: Wert 3 aktuell: Wert 3 gültig: 1 aktuell: Wert 3 key: 2 key/value: [2 -> Wert 3] nächstes: aktuell: gültig:
Hinweis: Für mehr Beispiele für die Benutzung von Iteratoren siehe auch SPL Erweiterung.
add a note
User Contributed NotesObjektiteration
Peter 'the Pete' de Pijd
01-Jul-2009 05:12
01-Jul-2009 05:12
hlegius at gmail dot com
15-Oct-2008 12:06
15-Oct-2008 12:06
Iterator interface usign key() next() rewind() is MORE slow than extends ArrayIterator with ArrayIterator::next(), ArrayIterator::rewind(), etc.,
wavetrex A(nospam)T gmail DOT com
01-Mar-2008 10:50
01-Mar-2008 10:50
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.
doctorrock83_at_gmail.com
18-May-2007 10:10
18-May-2007 10:10
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
artur at jedlinski dot pl
22-Apr-2007 07:38
22-Apr-2007 07:38
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
rune at zedeler dot dk
28-Feb-2007 04:00
28-Feb-2007 04:00
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.
baldurien at bbnwn dot eu
10-Aug-2006 01:01
10-Aug-2006 01:01
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...
chad 0x40 herballure 0x2e com
05-May-2006 01:46
05-May-2006 01:46
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);
}
?>
markushe at web dot de
06-Aug-2005 06:05
06-Aug-2005 06:05
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()
just_somedood at yahoo dot com
27-Jun-2005 07:20
27-Jun-2005 07:20
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 $aContact->get_name() . "\r\n";
}
?>
Would work just fine. This makes code so much simpler and easy to follow, it's great. This is exactly the direction I had hoped PHP5 was going!
PrzemekG_ at poczta dot onet dot pl
27-May-2005 11:20
27-May-2005 11:20
If you want to do someting like this:
<?php
foreach($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 ¤t()
{
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.
elias at need dot spam
10-Apr-2005 10:15
10-Apr-2005 10:15
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
strrev('ed.relpmeur@ekneos');
01-Mar-2005 10:25
01-Mar-2005 10:25
Use the SPL ArrayAccess interface to call an object as array:
http://www.php.net/~helly/php/ext/spl/interfaceArrayAccess.html
phpnet at nicecupofteaandasitdown dot com
22-Feb-2005 04:09
22-Feb-2005 04:09
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 $this->item;
}
knj at aider dot dk
19-Dec-2004 03:19
19-Dec-2004 03:19
if you in a string define classes that implements IteratorAggregate.
you cant use the default;
<?
...
public function getIterator() {
return new MyIterator($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();
}
...
?>