title: Can I find out if a filtered iterator is empty?
body: <p>I have a filtered iterator like so:</p>
  
  <pre><code>let filt_it = a_vector.iter().filter(|x| condition_on_x);
  </code></pre>
  
  <p>Is there a way I can find out whether it's empty?</p>
  
  <p>I need the iterator to <strong>stay an iterator</strong> for later use and it doesn't seem possible to clone filtered iterators.</p>