de">f</code> as it could escape this way and be
   mutated in the future -- <code class="code">string_init</code> would give up ownership of
   <code class="code">s</code> to pass it to <code class="code">f</code>, and could not call <code class="code">unsafe_to_string</code>
   safely.</p>

<p>We have provided the <a href="String.html#VALinit"><code class="code"><span class="constructor">String</span>.init</code></a>, <a href="String.html#VALmap"><code class="code"><span class="constructor">String</span>.m