Consumer.php

<?php


class Tx_MocBeer_Domain_Model_Consumer {

	/**
	 * @var Tx_MocBeer_Domain_Service_InventoryService
	 * @inject
	 */
	protected $inventoryService;

	/**
	 * @param Tx_MocBeer_Domain_Service_InventoryService $service
	 */
	public function injectInventoryService(Tx_MocBeer_Domain_Service_InventoryService $service) {
		$this->inventoryService = $service;
	}

	/**
	 * @param Tx_MocBeer_Domain_Model_Beer $beer
	 * @return void
	 */
	public function drinkBeer(Tx_MocBeer_Domain_Model_Beer $beer) {
		$beer->open();
		//@todo: Do actual drinking...
		$this->inventoryService->removeBeerFromInventory($beer);
	}
}

InventoryService.php

<?php


class Tx_MocBeer_Domain_Service_InventoryService implements t3lib_Singleton {

	/**
	 * @param Tx_MocBeer_Domain_Model_Beer $beer
	 */
	public function removeBeerFromInventory(Tx_MocBeer_Domain_Model_Beer $beer) {
		$message = date("d/m-Y H:i") . "\t" . $beer->getName() . ' removed from inventory';
		file_put_contents(PATH_site . 'typo3temp/moc_beer.log', $message . PHP_EOL, FILE_APPEND);
	}

}