 class="c1">// same as Loc, but operating over immutable values</span>
  <span class="k">typename</span> <span class="n">cached_location_t</span><span class="p">;</span> <span class="c1">// type to store relative location (for efficient repeated access)</span>
  <span class="k">typename</span> <span class="n">point_t</span>  <span class="o">=</span> <span class="n">difference_type</span><span class="p">;</span>

  <span class="k">static</span> <span class="k">const</span> <span class="kt">size_t</span> <spa