Can I use static class for my Logger?

Question

Recently I have been told that static class/methods are evil.

Take for example my class Logger:

class Logger{
   private static $logs = array();
   public static function add($msg){
      self::$logs[]=$msg;
   }

   public static function echo(){
       print_r(self::$logs);
   }
}

I can use whenever i want in my appliaction like this:

Logger::add('My log 1');

But reading this developers:

• http://misko.hevery.com/2008/12/15/static-methods-are-death-to-testability/

That Logger class doesn't seem so good.

So: Can I use it statically or I should avoid it at any cost?

Answer 1

Logging classes are the exception.

Since they rarely contain much logic, you don't have the same testing concerns.

Logging is a perfect example of a GOOD place to use static classes.

Think of your alternatives:

• A global instance of a logging object?
• A singleton logging object?
• Pass the logging object around to every single method/class (via in a constructor)?

The above are much worse than using static for logging.

Answer 2

Avoid it. I've seen quite some posts of you now struggling with the issue and people giving you bad advice. I'll repeat what I said in some of my answers/comments.

The way you use static in your logger class is to use it as a globally access point. Whenever you need to logg something you call Logger::log().

1) You will not be able to tell from looking at your class definition that it depends on the Logger class. Change in code thus becomes an adventure: 'I hope I will not break some hidden dependency when I change this tiny little ... OOPS!'.

2) It IS harder to test. You can't realiably test a class that sends a message to the Logger with Logger::log(). When a test fails how will you know it is not because the Logger fails? You would know if you could replace it with a mock, but in your case it is not mockable.

An alternative to explore:

Use the observer pattern and make the Logger an observer, the classes that need logging can be observables. They send messages like $this->observers->nofify('test succeeded').

You could use some other form of events too or dependency injection (automatic or manual). But please please don't call Logger::log() in a method.