/**
  * Constructor
  *
  * @param  int $index
  * @param  int $size
  * @param  parent $backing
  */
 public function __construct($index, $size, parent $backing)
 {
     parent::__construct($backing->variables, $backing->parent);
     $this->index = $index;
     $this->last = $size - 1;
     $this->backing = $backing;
 }
 /**
  * Constructor
  *
  * @param  string $key
  * @param  bool $first
  * @param  parent $backing
  */
 public function __construct($key, $first, parent $backing)
 {
     parent::__construct($backing->variables, $backing->parent);
     $this->key = $key;
     $this->first = $first;
     $this->backing = $backing;
 }