s iterable,
converts each one to a <a href="dart-core/String-class.html">String</a> by calling <a href="dart-collection/SetMixin/toString.html">Object.toString</a>,
and then concatenates the strings, with the
<code>separator</code> string interleaved between the elements.</p>
    </section>
    
    <section class="summary source-code" id="source">
      <h2><span>Implementation</span></h2>
      <pre class="language-dart"><code class="language-dart">String join([String separator = &quot;&quot;]) {
  Iterat