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<?php class foo implements ArrayAccess { private $container = array(); public function __construct() { $this->container = array(); } public function offsetSet($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; } } $foo = new foo(); $foo['bar'] = 1; var_dump(array_key_exists('bar', $foo));

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