n class="special">{</span>
            <span class="identifier">BOOST_CONTRACT_ASSERT</span><span class="special">(</span><span class="identifier">x</span> <span class="special">==</span> <span class="special">*</span><span class="identifier">old_x</span> <span class="special">+</span> <span class="number">1</span><span class="special">);</span> <span class="comment">// Line 20.</span>
        <span class="special">})</span>
    <span class="special">;</span>

    <span class="special">++</span><span class=