Q:

PHP implements ArrayAccess

I have two Classes viz foo & Bar
class bar extends foo
{

    public $element = null;

    public function __construct()
    {
    }
}

and the Class foo goes as 
class foo implements ArrayAccess
{

    private $data = [];
    private $elementId = null;

    public function __call($functionName, $arguments)
    {
        if ($this->elementId !== null) {
            echo "Function $functionName called with arguments " . print_r($arguments, true);
        }
        return true;
    }

    public function __construct($id = null)
    {
        $this->elementId = $id;
    }

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

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

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

    public function offsetGet($offset)
    {
        if (!$this->offsetExists($offset)) {
            $this->$offset = new foo($offset);
        }
    }
} 

i want that when i run the below piece of code:
$a = new bar();
$a['saysomething']->sayHello('Hello Said!');

should return Function sayHello Called with arguments Hello Said! from foo's __call magic method.
Here, i want to say is saysomething should be passed in $this->elementId from foo's __construct function and sayHello should be taken as method and Hello Said should be taken as parameters for sayHello Function which would be rendered from __call magic method.
Also, need to chain methods like:
$a['saysomething']->sayHello('Hello Said!')->sayBye('Good Bye!');

A:

If I'm not mistaken, you should change foo::offsetGet() to this:
public function offsetGet($offset)
{
    if (!$this->offsetExists($offset)) {
        return new self($this->elementId);
    } else {
        return $this->data[$offset];
    }
}

It returns an instance of itself if there's no element at the given offset.
That said, foo::__construct() should be called from bar::__construct() as well and be passed a value other than null:
class bar extends foo
{

    public $element = null;

    public function __construct()
    {
        parent::__construct(42);
    }
}

Update
To chain calls, you need to return the instance from __call():
public function __call($functionName, $arguments)
{
    if ($this->elementId !== null) {
        echo "Function $functionName called with arguments " . print_r($arguments, true);
    }
    return $this;
}

