title: PHP Constant doesn't exist: Notice
body: <p>I'd like to use constants as config variables within my PHP applications, only when a constant doesn't exist (for whatever reason) it throws me a notice but I'd like that to be an error (or exception), just like when I try to echo a not existing variable.</p>
  
  <p>Is that possible without using a separate function for getting constant values, something like this:</p>
  
  <pre><code>echo $non_existing_variable; // Error
  echo NON_EXISTING_CONSTANT; // Now also an error
  </code></pre>
  
  <p>Been searching around a bit but couldn't find anything.</p>
  
  <p>Seems kind of logical to me, when I try to use a variable that doesn't exist code execution quits immediately and throws an error, why isn't that with constants?</p>