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<?php interface CommandInterface {} abstract class AbstractCommand implements CommandInterface {} interface PrefixableCommandInterface { abstract class PrefixableCommand extends AbstractCommand implements PrefixableCommandInterface { } class StringSet extends PrefixableCommand {} interface ConnectionInterface {} class Connection implements ConnectionInterface { public function executeCommand(CommandInterface $command) { echo 'foo connection'; } } class Tester { private $connection; public function __construct() { $this->connection = new Connection(); } public function executeCommand(CommandInterface $command) { $this->connection->executeCommand($command); } } $t = new Tester(); $t->executeCommand(new StringSet);