ion, which performs a copy and is thus correct.</p>

<p>Assuming unique ownership of strings that are not string
    literals, but are (partly) built from string literals, is also
    incorrect. For example, mutating <code class="code">unsafe_of_string&nbsp;(<span class="string">"foo"</span>&nbsp;^&nbsp;s)</code>
    could mutate the shared string <code class="code"><span class="string">"foo"</span></code> -- assuming a rope-like
    representation of strings. More generally, functions operating on
    stri