able to selectively enable or disable
                    certain specializations of <code class="computeroutput"><span class="identifier">clear_value</span></code>
                    utilizing SFINAE (i.e. <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">enable_if</span></code>
                    or <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">disable_if</s