PHP Iterator like mysql iterator? - php

Question

Already I extended and implemented from SPL iterator.
But if I want to use it, I should use it on a foreach.
I tried to use it in a while like this:
$news = new testClass();
while( $row = $news )
echo $row["name"];
It will create an infinite loop !
But with foreach, it works fine!
Here is top of my class:
class testClass implements \Iterator
Where is the mistake ?

Answer 1

Fist, bravo on using the SPL classes for this type of 'standard' problem. Too often have I seen inexperienced/sloppy developers (or even good ones that simply don't think ahead) reinvent the wheel in these types of situations.
You're missing some very important details about the implementation of the iterator interface.
see PHP:Iterator - Manual for more information, and the reference implementation from below.
First, you need to implement the, rewind, current, key, next, and valid functions. the reference implementation looks like this:
class myIterator implements Iterator {
private $position = 0;
private $array = array(
"firstelement",
"secondelement",
"lastelement",
);
public function __construct() {
$this->position = 0;
}
function rewind() {
var_dump(__METHOD__);
$this->position = 0;
}
function current() {
var_dump(__METHOD__);
return $this->array[$this->position];
}
function key() {
var_dump(__METHOD__);
return $this->position;
}
function next() {
var_dump(__METHOD__);
++$this->position;
}
function valid() {
var_dump(__METHOD__);
return isset($this->array[$this->position]);
}
}
)
And the code for traversing that implementation looks like this:
$it = new myIterator;
foreach($it as $key => $value) {
var_dump($key, $value);
echo "\n";
}

Answer 2

foreach is language construct that iterates through all elements. while executes block of code until given condition is true. To make it work you have to use your own function that checks for valid key and returns current element.

Answer 3

Finally I created a simple example of this:
<?php
/**
* #author Soroush Khosravi
* #copyright 2013
*/
class _Iterator
{
private $array;
public function setArray(array $data)
{
$this->array = $data;
}
public function reader()
{
if (is_null($this->array))
return false;
$elem = array_shift($this->array);
if (count ($this->array) > 0)
return $elem;
return false;
}
}
Class child extends _Iterator
{
function execute()
{
$this->setArray(array(1,2,3,4,5,6));
return $this;
}
}
$obj = new child;
$obj = $obj->execute();
while($row = $obj->reader())
echo $row;
?>