70   public function offsetExists($offset)  argument
72     if (!is_numeric($offset)) {
73       return parent::offsetExists($offset);
75     return isset($this->{$this->collection_key}[$offset]);
79   public function offsetGet($offset)  argument
81     if (!is_numeric($offset)) {
82       return parent::offsetGet($offset);
84     $this->coerceType($offset);
85     return $this->{$this->collection_key}[$offset];
89   public function offsetSet($offset, $value)  argument
91     if (!is_numeric($offset)) {
92       parent::offsetSet($offset, $value);
94     $this->{$this->collection_key}[$offset] = $value;
98   public function offsetUnset($offset)  argument
100     if (!is_numeric($offset)) {
101       parent::offsetUnset($offset);
103     unset($this->{$this->collection_key}[$offset]);
106   private function coerceType($offset)  argument
109     if ($keyType && !is_object($this->{$this->collection_key}[$offset])) {
110       $this->{$this->collection_key}[$offset] =
111           new $keyType($this->{$this->collection_key}[$offset]);