f &lt;list&lt;int&gt;&gt; 1
#&gt; $ vctrs_vctr    &lt;vctrs_vc&gt; 1
#&gt; $ quosures      &lt;quos&gt; &lt;~1&gt;</code></pre>
</div>
<div id="implementation" class="section level2">
<h2>Implementation</h2>
<p>The column header is obtained by calling
<code>pillar::type_sum()</code> on the column. This is an S3 method that
can be overridden, but most of the time it is more useful to override
<code>vctrs::vec_ptype_abbr()</code>:</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode r"><code class="sou