span class="keyword">typename</span> T<span class="special">&gt;</span> <a class="link" href="mean.html" title="Class template mean">mean</a> <span class="special">&amp;</span> <a class="link" href="mean.html#idm45106007683664-bb"><span class="keyword">operator</span><span class="special">+=</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="mean.html" title="Class template mean">mean</a><span class="special">&lt;</span> <span class="identifier">T</span> <span c