pan class="keyword">typename</span> <span class="identifier">T</span><span class="special">::</span><span class="identifier">difference_type</span><span class="special">;</span>

<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_detected_exact_v</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">ptrdiff_t</span><s