What is the best way to inject a logger?

I'm working on several projects right now that I'd like to be able to generate logs from.

The problem is that logging isn't required for the code to work, so how do I configure it?

I see three possibilities:

Required in Constructor

use Psr\Log\LoggerInterface;
class MyClass {
  private $logger;
  public function __construct(LoggerInterface $logger) {
  }
}

Pros

Cleanest implementation

Cons

Requires user to pass in a logger even if they don't want to log anything

Optional in Constructor

use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
class MyClass {
  private $logger;
  public function __construct(LoggerInterface $logger = null) {
    if (is_null($logger)) {
    }
    $this->logger = $logger;
  }
}

Pros

No longer requires the user to pass in a logger

Cons

Clutters up the constructor
I consider using null a code smell

Optional setLogger Method

use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
class MyClass {
  private $logger;
  public function __construct() {
  }
  public function setLogger(LoggerInterface $logger) {
  }
}

Pros

Clean constructor
No nulls

Cons

Instantiating with a logger requires two statements

Summary

I'm leaning toward the third method for my packages even though it doesn't feel like an ideal solution. It just feels better than the other two.

How are you handling injecting an optional logger? Let me know in the comments.

Published March 6, 2017