above example, <code class="computeroutput"><span class="identifier">expression1</span></code>
            and <code class="computeroutput"><span class="identifier">expression2</span></code> have
            result type <code class="computeroutput"><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</span></code>
            and <code class="computeroutput"><span class="keyword">decltype</span><span class="special">(</span><span class="