gistfile1.php

<?php

class LogManager {
    protected $logger;
    public function __construct($logger) {
        $this->logger = $loggervar;
    }

    public function log($msg, $level)
    {
        $this->logger->write($msg,$level);
    }
}

class FileLogger {
    public function write($msg, $level)
    {
        File::wite($msg, $level);
    }
}

class RedisLogger {
    public function write($msg, $level)
    {
        Redis::write($msg,$level);
    }
}

class NullLogger {
    public function write()
    {
        // Do nothing
    }
}

$logManager = new LogManager(new FileLogger);
$logManager->log('Log to file', 'ALERT');

$logManager = new LogManager(new MemoryLogger);
$logManager->log('Log to redis memory', 'ALERT');

$logManager = new LogManager(new NullLogger);
$logManager->log('Do nothing', 'ALERT');