Simple example of prototype OOP in PHP.

example.php

<?php

// Create and spec a new prototype for animals.

$animal = new Object;
$animal->is_animal = true;

// Create and spec a new prototype for dogs.

$dog = new Object($animal);
$dog->bark = function () {
  echo 'Woof!', PHP_EOL;
};

// Create our useful object.

$lucky = new Object($dog);
$lucky->name = 'Lucky';

echo $lucky->name, PHP_EOL; // Lucky

$lucky->bark(); // Woof!

if ($lucky->is_animal) // true
  echo 'Hooray!';

Prototype.php

<?php

/**
 * The prototype class.
 */
class Object
{
  /**
   * The object's data.
   */
  private $__hash = [];
  
  /**
   * The object's prototype.
   */
  private $prototype = null;
  
  /**
   * Make a blank prototype by default.
   */
  public function __construct($prototype = null)
  {
    $this->prototype = $prototype ?? new stdClass;
  }

  /**
   * Get a property.
   * @param string $name
   */
  public function __get(string $key)
  {
    return $this->__hash[$key] ?? $this->prototype->$key ?? null;
  }

  /**
   * Add a new variable, function or otherwise.
   * @param string $name The variable's name.
   * @param callable $function
   */
  public function __set(string $name, $value)
  {
    $this->__hash[$name] = $value;
  }

  /**
   * Call a method in the prototype.
   * @param string $function
   * @param array $params
   * @return mixed
   */
  public function __call($function, array $params)
  {
    if (!is_callable($this->$function))
      throw new \InvalidArgumentException;

    return $this->$function->call($this, ...$params);
  }

  /**
   * Resets this object's prototype.
   * @param Object $that
   * @return Object $this
   */
  public function extend(Object $that)
  {
    $this->prototype = $that;
  }
}