title: What does a plus sign mean in a hash?
body: <p>I have the following piece of Perl code, but I can't understand what its doing.</p>
  
  <pre><code>use constant ANIMAL =&gt; 'rabbit'; 
  if ($self-&gt;{+ANIMAL}) {
      # Do something here
  }
  </code></pre>
  
  <p>What does the <code>+</code> sign before the constant <code>ANIMAL</code> mean?</p>