title: purrr::map_int: Can't coerce element 1 from a double to a integer
body: <p>I am having the weirdest bug with <code>map_int</code> from the <code>purrr</code> package. </p>
  
  <pre class="lang-r prettyprint-override"><code># Works as expected
  purrr::map_int(1:10, function(x) x)
  #&gt;  [1]  1  2  3  4  5  6  7  8  9 10
  
  # Why on earth is that not working?
  purrr::map_int(1:10, function(x) 2*x)
  #&gt; Error: Can't coerce element 1 from a double to a integer
  
  # or that?
  purrr::map_int(1:10, round)
  #&gt; Error: Can't coerce element 1 from a double to a integer
  </code></pre>
  
  <p><sup>Created on 2019-03-28 by the <a href="https://reprex.tidyverse.org" rel="nofollow noreferrer">reprex package</a> (v0.2.1)</sup></p>
  
  <p>I run 3.5.2 in rocker container (Debian) with the latest github version of everything:</p>
  
  <pre class="lang-r prettyprint-override"><code>sessioninfo::package_info("purrr")
  #&gt;  package  * version    date       lib source                             
  #&gt;  magrittr   1.5.0.9000 2019-03-28 [1] Github (tidyverse/magrittr@4104d6b)
  #&gt;  purrr      0.3.2.9000 2019-03-28 [1] Github (tidyverse/purrr@25d84f7)   
  #&gt;  rlang      0.3.2.9000 2019-03-28 [1] Github (r-lib/rlang@9376215)       
  #&gt; 
  #&gt; [1] /usr/local/lib/R/site-library
  #&gt; [2] /usr/local/lib/R/library
  </code></pre>