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

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

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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

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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.

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