"special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">use_default</span><span class="special">,</span> 
         <span class="keyword">typename</span> DifferenceType <span class="special">=</span> <span class="special">::</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">ptrdiff_t</span><span class="special">,</span> 
         <span class="keyword">typename</span> ValueType <span class="special">=</span>