code: public function addArgument(ArgumentInterface $argument)
  	{
  		$this->argumentPositions[$argument->getPosition()] = $argument;
  		$this->argumentNames[$argument->getName()] = $argument;
  		if ($argument->isClass()) {
  			$this->argumentClasses[$argument->getClass()] = $argument;
  		}
  		return $argument;
  	}
docs: Add an argument to the factory definition.
  
  @param ArgumentInterface $argument