nnotation">S</span> <span class="parameter-name">previous</span>, </span> <span class="parameter" id="combine-param-element"><span class="type-annotation">T</span> <span class="parameter-name">element</span></span>)</span>)
            <span class="returntype parameter">&#8594; <a href="dart-async/Future-class.html">Future</a><span class="signature">&lt;<wbr><span class="type-parameter">S</span>&gt;</span></span>
          </span>
                  </dt>
        <dd class="inherited">
          Combines a s