Introduction
Iterator interface extends abstract Traversable interface. PHP provides many built-in iterators (called SPL iterators) for many routine functionalities. Examples are ArrayIterator, DirectoryIterator etc. A user class that implements Iterator interface should implement abstract methods as defined in it.
Syntax
Iterator extends Traversable {
/* Methods */
abstract public current ( void ) : mixed
abstract public key ( void ) : scalar
abstract public next ( void ) : void
abstract public rewind ( void ) : void
abstract public valid ( void ) : bool
}Methods
Iterator::current — Return the current element
Iterator::key — Return the key of the current element
Iterator::next — Move forward to next element
Iterator::rewind — Rewind the Iterator to the first element
Iterator::valid — Checks if current position is valid
When implementing IteratorAggregate or Iterator interface which extends Traversable, they must be listed before its name in the implements clause.
Iterator Example
In following PHP script, a class that implements Interface contains an array as private variable. Implementing abstract methods of Iterator, we can traverse the array using foreach loop as well with next() method.
Example
<?php
class myIterator implements Iterator {
private $index = 0;
private $arr = array(10,20,30,40);
public function __construct() {
$this->index = 0;
}
public function rewind() {
$this->index = 0;
}
public function current() {
return $this->arr[$this->index];
}
public function key() {
return $this->index;
}
public function next() {
++$this->index;
}
public function valid() {
return isset($this->arr[$this->index]);
}
}
?>Using foreach loop, we can iterate over array property of MyIterator object
$it = new myIterator();
foreach($it as $key => $value) {
echo "$key=>". $value ."\n";
}Iteration can also be performed by clling next() method in a while loop. Make sure to rewind the iterator before commencing loop
Example
$it->rewind();
do {
echo $it->key() . "=>" .$it->current() . "\n";
$it->next();
}
while ($it->valid());Output
On both occasions, traversal of array property shows following result
0=>10 1=>20 2=>30 3=>40