code: public function addOptionalScalarArgument($name, $type, $default)
  	{
  		return $this->addArgument(new ScalarArgument($this->argumentPosition++, $name, $type, false, $default));
  	}
docs: Add an optional scalar argument to the factory definition.
  
  @param string  $name
  @param string  $type    int, string, object, etc.
  @param mixed   $default