Difference between ArrayIterator, ArrayObject and Array in PHP

Question

Can somebody explain clearly the fundamental differences between ArrayIterator, ArrayObject and Array in PHP in terms of functionality and

Answer 1

EDIT:forgot to address the normal array in my answer..

Before you read all this, if your new to php and not trying to do anything tricky just storing values to be used later, then just use the array primitive type.

$data = [1,2,3,4,5];
//or
$data = array(1,2,3,4,5);

Array is the entry point and you should get used to using first them before considering using the others. If you do not understand arrays then you will probably will not understand the benefits of using the others. ( See https://www.w3schools.com/php/php_arrays.asp for a tutorial on arrays. )

Otherwise continue reading...

I have the same question and after coming here decided to just spend some time testing them out and here is my findings and conclusions...

First lets clear up some things that were said by others that I immediately tested.

ArrayObject and ArrayItterator do not protect the data. Both can still be passed by reference in a for-each loop (see down he bottom for example).

Both return true for is_object(), both return false for is_array() and both allow direct access to the values as an array without providing protection for adding values etc. and both can be passed by reference allowing the original data to be manipulated during a foreach loop.

$array = new ArrayIterator();
var_dump(is_array($array)); // false
var_dump(is_object($array)); // true
$array[] = 'value one';
var_dump($array[0]);//string(9) "value one"

$array = new ArrayObject();
var_dump(is_array($array)); // false
var_dump(is_object($array)); // true
$array[] = 'value one';
var_dump($array[0]);//string(9) "value one"

The big difference can be seen in the functions that are available for either of them.

ArrayIteroator has all the functions required to traverse the values such as a foreach loop. ( A foreach loop will call rewind(),valid(),current(),key() methods ) see: https://www.php.net/manual/en/class.iterator.php for an excellent example of the concept (lower level class documentation).

While an ArrayObject can still be iterated over and access values the same way, it does not offer public access to pointer functions.

Object is kind of like adding a wrapper arount the ArrayItterator object and has public getIterator ( void ) : ArrayIterator that will faciliate traversing of the values inside.

You can always get the ArrayItterator From ArrayObject if your really need the added functions.

ArrayItterator is best choice if you have your own pseudo foreach loop for traversing in weird ways and want better control instead of just start to end traversal.

ArrayItterator would also be a good choice for overriding the default array behavior when iterated over by a foreach loop. eg..

//I originally made to this to solve some problem where generic conversion to XML via a foreach loop was used,
//and I had a special case where a particular API wanted each value to have the same name in the XML.
class SameKey extends ArrayIterator{

    public function key()
    {
        return "AlwaysTheSameKey";
    }
}

$extendedArrayIterator =  new SameKey(['value one','value two','value three']);
$extendedArrayIterator[] = 'another item added after construct';
//according to foreach there all the keys are the same
foreach ($extendedArrayIterator as $key => $value){
    echo "$key: ";//key is always the same
    var_dump($value);
}
//can still be access as array with index's if you need to differentiate the values
for ($i = 0; $i < count($extendedArrayIterator); $i++){
    echo "Index [$i]: ";
    var_dump($extendedArrayIterator[$i]);
}

The ArrayObject might be a good choice if you have more high level complexities with itterators going on for example...

//lets pretend I have many custom classes extending ArrayIterator each with a different behavior..
$O = new ArrayObject(['val1','val2','val3']);
//and I want to change the behavior on the fly dynamically by changing the iterator class
if ($some_condition = true) $O->setIteratorClass(SameKey::class);
foreach ($O as $key => $value){
    echo "$key: ";//AlwaysTheSameKey:
    var_dump($value);
}

One example might be changing the output of the same data set such as having a bunch of custom iterators that will return the values in a different format when traversing the same data set. eg...

class AustralianDates extends ArrayIterator{
    public function current()
    {
        return Date('d/m/Y',parent::current());
    }
}
$O = new ArrayObject([time(),time()+37474,time()+37845678]);
//and I want to change the behaviour on the fly dynamically by changing the iterator class
if ($some_condition = true) $O->setIteratorClass(AustralianDates::class);
foreach ($O as $key => $value){
    echo "$key: ";//AlwaysTheSameKey:
    var_dump($value);
}

Obviously there are probably better ways to do this kind of thing.

In short these are the major major advantages differences I can see.

ArrayItorator - lower level ability to control or extend & override traversal behaviors.

VS

ArrayObject - one Container for data but able to change ArrayIterator class.

There are also other differences you might care to inspect but I'd imagine you wont fully grasp them all until you use them extensively.

It appears both objects can be used by reference in a foreach but NOT when using a custom itterator class via an ArrayObject..

//reference test
$I = new ArrayIterator(['mouse','tree','bike']);
foreach ($I as $key => &$value){
    $value = 'dog';
}
var_dump($I);//all values in the original are now 'dog'

$O = new ArrayObject(['mouse','tree','bike']);
foreach ($O as $key => &$value){
    $value = 'dog';
}
var_dump($O);//all values in the original are now 'dog'

$O->setIteratorClass(SameKey::class);
foreach ($O as $key => &$value){//PHP Fatal error:  An iterator cannot be used with foreach by reference
    $value = 'dog';
}
var_dump($O);

Recommendation/Conclusion

Use arrays.

If you want to do something tricky then, I'd recommend always using ArrayIterator to start off with and only move on to ArrayObject if you want to something specific that only ArrayObject can do.

Considering the ArrayObject can make use of any custom ArrayIterators you have created along the way, id say this is the logical path to take.

Hope this helps you as much as it helped me looking into it.

Answer 2

array is one the eight primitive types in PHP. Allthough it comes with a lot of built-in utility functions, but they are all procedural.

Both the ArrayObject and the ArrayIterator allow us to make arrays first class citizens in an object oriented program (OOP).

Difference between ArrayObject and the ArrayIterator is that, since ArrayIterator implements SeekableIterator interface, you can do $myArray->seek(10); with ArrayIterator.

Answer 3

Array is a native php type. You can create one using the php language construct array(), or as of php 5.4 onwards []

ArrayObject is an object that work exactly like arrays. These can be created using new keyword

ArrayIterator is like ArrayObject but it can iterate on itself. Also created using new

---

Comparing Array vs (ArrayObject/ArrayIterator)

They both can be used using the php's array syntax, for eg.

$array[] = 'foo';
$object[] = 'foo';
// adds new element with the expected numeric key

$array['bar'] = 'foo';
$object['bar'] = 'foo';
// adds new element with the key "bar"

foreach($array as $value);
foreach($object as $value);
// iterating over the elements

However, they are still objects vs arrays, so you would notice the differences in

is_array($array); // true
is_array($object); // false

is_object($array); // false
is_object($object); // true

Most of the php array functions expect arrays, so using objects there would throw errors. There are many such functions. For eg.

sort($array); // works as expected
sort($object); // Warning: sort() expects parameter 1 to be array, object given in ......

Finally, objects can do what you would expect from a stdClass object, i.e. accessing public properties using the object syntax

$object->foo = 'bar'; // works
$array->foo = 'bar'; // Warning: Attempt to assign property of non-object in ....

Arrays (being the native type) are much faster than objects. On the other side, the ArrayObject & ArrayIterator classes have certain methods defined that you can use, while there is no such thing for arrays

---

Comparing ArrayObject vs ArrayIterator

The main difference between these 2 is in the methods the classes have.

The ArrayIterator implements Iterator interface which gives it methods related to iteration/looping over the elements. ArrayObject has a method called exchangeArray that swaps it's internal array with another one. Implementing a similar thing in ArrayIterator would mean either creating a new object or looping through the keys & unseting all of them one by one & then setting the elements from new array one-by-one.

Next, since the ArrayObject cannot be iterated, when you use it in foreach it creates an ArrayIterator object internally(same as arrays). This means php creates a copy of the original data & there are now 2 objects with same contents. This will prove to be inefficient for large arrays. However, you can specify which class to use for iterator, so you can have custom iterators in your code.

---

Hope this is helpful. Edits to this answer are welcome.

Answer 4

ArrayObject and array are somewhat alike. Merely a collection of objects (or native types). They have some different methods that you can call, but it mostly boils down to the same thing.

However, an Iterator is something else completely. The iterator design pattern is a way to secure your array (making it only readable). Lets take the next example:

You have a class that has an array. You can add items to that array by using addSomethingToMyArray. Note however, that we do something to item before we actually add it to the array. This could be anything, but lets for a moment act like it is very important that this method is fired for EVERY item that we want to add to the array.

class A
{
    private $myArray;
    public function returnMyArray()
    {
        return $this->myArray;
    }

    public function addSomethingToMyArray( $item )
    {
        $this->doSomethingToItem( $item ); 
        array_push( $item );
    }
}

The problem with this, is that you pass the array by reference here. That means that classes that actually use returnMyArray get the real myArray object. That means that classes other than A can add things to that array, and therefor also change the array inside A without having to use the addSOmethingToMyArray. But we needed to doSOmethingToItem, remember? This is an example of a class not in control of its own inner status.

The solution to this is an iterator. Instead of passing the array, we pass the array to a new object, that can only READ things from the array. The most simple Iterator ever is something like this:

<?php

class MyIterator{

    private $array;
    private $index;

    public function __construct( $array )
    {
        $this->array = $array;
    }

    public function hasNext()
    {
        return count( $this->array ) > $this->index;
    }

    public function next()
    {
        $item = $this->array[ $this->index ];
        this->$index++;

        return $item;
    }       
}

?>

As you can see, i have no way of adding new items to the given array, but i do have posibilities to read the array like this:

while( $iterator->hasNext() )
    $item = $iterator->next();

Now there is again, only one way to add items to myArray in A, namely via the addSomethingToArray method. So that is what an Iterator is, it is somewhat of a shell around arrays, to provide something called encapsulation.

Answer 5

• Arrays

An array in PHP is actually an ordered map. A map is a type that associates values to keys. This type is optimized for several different uses; it can be treated as an array, list (vector), hash table (an implementation of a map), dictionary, collection, stack, queue, and probably more. As array values can be other arrays, trees and multidimensional arrays are also possible.

• The ArrayObject class

This class allows objects to work as arrays.

• The ArrayIterator class

This iterator allows to unset and modify values and keys while iterating over Arrays and Objects.

When you want to iterate over the same array multiple times you need to instantiate ArrayObject and let it create ArrayIterator instances that refer to it either by using foreach or by calling its getIterator() method manually.

Answer 6

An Iterator is an object that enables a programmer to traverse a container, particularly lists. Various types of iterators are often provided via a container's interface.

There is no much difference between ArrayObject and Array as they represent the same things albeit using different object types.

ArrayIterator is an Iterator that iterates over Array-like objects, this includes all objects that implement ArrayAcess and the native Array type. In fact, when you foreach over an array, PHP internally creates ArrayIterator to do the traversing and transform your code to look as if typed this,

for( $arrayIterator->rewind(); $arrayIterator->valid(); $arrayIterator-
>next())
{    $key = $arrayIteartor->key();
     $value = $arrayIterator->current();
}

So you can see, every collection object has an Iterator except for your defined collections which you need to define your own Iterators for.