title: reprex can't find the ref() function
body: <pre class="lang-r prettyprint-override"><code>x &lt;- list(1:10)
  ref(x)
  #&gt; Error in ref(x): could not find function "ref"
  
  tracemem(x)
  #&gt; [1] "&lt;0000000017E74B50&gt;"
  
  x[[2]] &lt;- x
  #&gt; tracemem[0x0000000017e74b50 -&gt; 0x00000000164836e8]:
  
  ref(x)
  #&gt; Error in ref(x): could not find function "ref"
  </code></pre>
  
  <p>I wanted to make a reproducible example with reprex. But it can't find the function ref. I loaded the lobstr package. Why is that happening can you tell me? </p>