Strange error: "Couldn't find constant Logger::DEBUG" when using Monolog in Laravel

Question

I've got a simple class that allows me to write to any log file:

use Monolog\Logger;
use Monolog\Handler\StreamHandler;

class Mylog
{
   public function __construct($log, $level = 'debug')
   {
      $this->monolog = new Logger($log);

      $level = constant('Logger::'.strtoupper($level));

      $this->monolog->pushHandler(new StreamHandler(storage_path('logs/'.$log.'-'.date('Y-m-d').'.txt')), $level);
   }

   public function __call($method, $arguments)
   {
      $this->monolog->{$method}($arguments[0]);
   }
}

This gives me the error: constant(): Couldn't find constant Logger::DEBUG

However, when pushing the handler, if I replace $level with simply Logger::DEBUG, it works. Why is it not finding the constant when it does, in fact, exist?

Answer 1

The class name inside a string like in the argument to the constant() function must be fully qualified. When you do Logger::DEBUG it works because the class is use'd, so it resolves as Monolog\Logger::DEBUG but in the string it just remains Logger::DEBUG and that obviously does not exist.

Therefore the solution is simply to use the fully qualified name within strings, i.e.

$level = constant('Monolog\Logger::'.strtoupper($level));