span><span class="p">:</span> <span class="kt">Element</span><span class="p">,</span> <span class="nv">willChange</span><span class="p">:</span> <span class="p">((</span><span class="kt">Element</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="kt">Void</span><span class="p">)?</span> <span class="o">=</span> <span class="kc">nil</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="kt">ReplayLastSubjectType</span><span class="o">&lt;</span><span class="kt">Element<