title: Laravel in_array validation rule
body: <p>I have defined an array</p>
  
  <pre><code>$this-&gt;allslots=array('10:00:00', '10:10:00', '10:20:00', '10:30:00', '10:40:00', '10:50:00', '11:00:00', '11:10:00', '11:20:00', '11:30:00', '11:40:00', '11:50:00', '12:00:00', '12:10:00', '12:20:00', '12:30:00', '12:40:00', '12:50:00', '13:00:00', '13:10:00', '13:20:00', '13:30:00', '13:40:00', '13:50:00', '14:00:00', '14:10:00', '14:20:00', '14:30:00', '14:40:00', '14:50:00', '15:00:00', '15:10:00', '15:20:00', '15:30:00', '15:40:00', '15:50:00', '16:00:00', '16:10:00', '16:20:00', '16:30:00', '16:40:00', '16:50:00');
  </code></pre>
  
  <p>Now, I want to validate before saving data to database that, if a given input matches one of the value of the above array. For this I'm doing</p>
  
  <pre><code>$this-&gt;validate($request, [
  
          'field' =&gt; 'required|in_array:$this-&gt;allslots',
      ]);
  </code></pre>
  
  <p>But, this returns validation error for every input. So, how can I do this?</p>