Matrix.opApply

{
      auto m = Matrix3i
      (
           3, -1, 6,
           2,  1, 5,
          -3,  1, 0
      );

      // Let's iterate matrix by element number
      size_t index;
      foreach (i, ref element; m)
      {
          if (element == 5)
          {
              index = i;
              break;
          }
      }
      assert (index == 5);

      // Let's iterate matrix with line and column number
      size_t line, col;
      foreach (i, j, ref element; m)
      {
          if (element == 5)
          {
              line = i;
              col = j;
              break;
          }
      }
      assert (line == 1 && col == 2);