n class="n">num_dimensions</span><span class="p">;</span> <span class="c1">// dimensionality of the locator</span>
  <span class="n">where</span> <span class="n">num_dimensions</span> <span class="o">=</span> <span class="n">point_t</span><span class="o">::</span><span class="n">num_dimensions</span><span class="p">;</span>

  <span class="c1">// The difference_type and iterator type along each dimension. The iterators may only differ in</span>
  <span class="c1">// difference_type. Their value_type must be