Why is the const&& overload of as_const deleted? : <p>On a <a href="http://talesofcpp.fusionfenix.com/post-23/interlude" rel="noreferrer">blog on the progress of C++17</a> I read the following:</p>

<blockquote>
  <p><code>P0007</code> proposes a helper function template <code>as_const</code>, which simply
  takes a reference and returns it as a reference to <code>const</code>.</p>

<pre><code>template &lt;typename T&gt; std::add_const_t&lt;T&gt;&amp; as_const(T&amp; t) { return t }
template &lt;typename T&gt; void as_const(T const&amp;&amp;) = delete;
</code></pre>
</blockquote>

<p>Why is the <code>const&amp;&amp;</code> overload deleted?</p>
