"Indirect modification of overloaded element of SplFixedArray has no effect"

First, the problem is related to all classes which implement ArrayAccess it is not a special problem of SplFixedArray only.

When you accessing elements from SplFixedArray using the [] operator it behaves not exactly like an array. Internally it's offsetGet() method is called, and will return in your case an array - but not a reference to that array. This means all modifications you make on $a[0] will get lost unless you save it back:

Workaround:

$a = new SplFixedArray(5);$a[0] = array(1, 2, 3); // get element$element = $a[0];// modify it$element[0] = 12345;// store the element again$a[0] = $element;var_dump($a);

Here is an example using a scalar which fails too - just to show you that it is not related to array elements only.

This is actually fixable if you slap a & in front of offsetGet (assuming you have access to the internals of your ArrayAccess implementation):

class Dict implements IDict {    private $_data = [];    /**     * @param mixed $offset     * @return bool     */    public function offsetExists($offset) {        return array_key_exists(self::hash($offset), $this->_data);    }    /**     * @param mixed $offset     * @return mixed     */    public function &offsetGet($offset) {        return $this->_data[self::hash($offset)];    }    /**     * @param mixed $var     * @return string     */    private static function hash($var) {        return is_object($var) ? spl_object_hash($var) : json_encode($var,JSON_UNESCAPED_SLASHES);    }    /**     * @param mixed $offset     * @param mixed $value     */    public function offsetSet($offset, $value) {        $this->_data[self::hash($offset)] = $value;    }    /**     * @param mixed $offset     */    public function offsetUnset($offset) {        unset($this->_data[self::hash($offset)]);    }}

Adding my experience with the same error, in case it helps anyone:

I recently imported my code into a framework with a low error-tolerance (Laravel). As a result, my code now throws an exception when I try to retrieve a value from an associative array using a non-existent key. In order to deal with this I tried to implement my own dictionary using the ArrayAccess interface. This works fine, but the following syntax fails:

$myDict = new Dictionary();$myDict[] = 123;$myDict[] = 456;

And in the case of a multimap:

$properties = new Dictionary();$properties['colours'] = new Dictionary();$properties['colours'][] = 'red';$properties['colours'][] = 'blue';

I managed to fix the problem with the following implementation:

<?phpuse ArrayAccess;/** * Class Dictionary * * DOES NOT THROW EXCEPTIONS, RETURNS NULL IF KEY IS EMPTY * * @package fnxProdCrawler */class Dictionary implements ArrayAccess{    // FOR MORE INFO SEE: http://alanstorm.com/php_array_access    protected $dict;    function __construct()    {        $this->dict = [];    }    // INTERFACE IMPLEMENTATION - ArrayAccess    public function offsetExists($key)    {        return array_key_exists($key, $this->dict);    }    public function offsetGet($key)    {        if ($this->offsetExists($key))            return $this->dict[$key];        else            return null;    }    public function offsetSet($key, $value)    {        // NOTE: THIS IS THE FIX FOR THE ISSUE "Indirect modification of overloaded element of SplFixedArray has no effect"        // NOTE: WHEN APPENDING AN ARRAY (E.G. myArr[] = 5) THE KEY IS NULL, SO WE TEST FOR THIS CONDITION BELOW, AND VOILA        if (is_null($key))        {            $this->dict[] = $value;        }        else        {            $this->dict[$key] = $value;        }    }    public function offsetUnset($key)    {        unset($this->dict[$key]);    }}

Hope it helps.