Why does a class that implements ArrayAccess, Iterator, and Countable not work with array_filter()?

Question

I have the following class:

<?php

/*
* Abstract class that, when subclassed, allows an instance to be used as an array.
* Interfaces `Countable` and `Iterator` are necessary for functionality such as `foreach`
*/
abstract class AArray implements ArrayAccess, Iterator, Countable
{
    private $container = array();

    public function offsetSet($offset, $value) 
    {
        if (is_null($offset)) {
            $this->container[] = $value;
        } else {
            $this->container[$offset] = $value;
        }
    }

    public function offsetExists($offset) 
    {
        return isset($this->container[$offset]);
    }

    public function offsetUnset($offset) 
    {
        unset($this->container[$offset]);
    }

    public function offsetGet($offset) 
    {
        return isset($this->container[$offset]) ? $this->container[$offset] : null;
    }

    public function rewind() {
            reset($this->container);
    }

    public function current() {
            return current($this->container);
    }

    public function key() {
            return key($this->container);
    }

    public function next() {
            return next($this->container);
    }

    public function valid() {
            return $this->current() !== false;
    }   

    public function count() {
     return count($this->container);
    }

}

?>

Then, I have another class that sub-classes AArray:

<?php

require_once 'AArray.inc';

class GalleryCollection extends AArray { }

?>

When I fill a GalleryCollection instance with data and then try to use it in array_filter(), in the first argument, I get the following error:

Warning: array_filter() [function.array-filter]: The first argument should be an array in

Answer 1

Because array_filter only works with arrays.

Look at other options, like FilterIterator, or create an array from your object first.