PHP Iterable interface

Introduction

Iterator interface extends the abstract Traversable interface. PHP provides a number of built-in iterators (called SPL iterators) for many common functions. For example ArrayIterator, DirectoryIterator, etc. User classes that implement the Iterator interface should implement the abstract methods 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 — Returns the current element

Iterator::key —Returns the key of the current element

Iterator::next — Move to the next element

Iterator::rewind — Rewind the iterator to the first element

Iterator::valid — Check if the current position is valid

When implementing the IteratorAggregate or Iterator interface, they must be listed before their name in the implements clause.

Iterator Example

In the following PHP script, a class that implements an interface contains a private variable as an array. By implementing the abstract method of iterator, we can iterate over the array using the foreach loop and the 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 a foreach loop, we can iterate over the array properties of the MyIterator object

$it = new myIterator();
foreach($it as $key => $value) {
   echo "$key=>". $value ."</p><p>";
}

Iteration can also be done by calling it in a while loopnext() method to execute. Make sure to rewind the iterator before starting the loop.

Example

$it->rewind();
do {
   echo $it->key() . "=>" .$it->current() . "</p><p>";
   $it->next();
}
while ($it->valid());

Output

In both cases, the traversal over the array properties shows the following results

0=>10
1=>20
2=>30
3=>40

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