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

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:

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.