Multidimensional slice

[Remi Thebault via Digitalmars-d-learn]

Hello D-community

Sorry to dig an old post, but I have the exact same need.
I have C++ background and I started to use D a few days ago only
(a pity I didn't start sooner!)

My needs are mostly around numerical calculations. I have a safe
and efficient matrix type in C++ that I am porting to D.

Implementation is really easier, no doubt.
I have coded slicing following this page
http://dlang.org/operatoroverloading.html#Slice
but the code doesn't compile.

here is a reduced and simplified code:



struct slice
{
      uint start;
      uint size;
}


struct Example
{
      int[] array;
      uint rows;
      uint cols;

      uint start;
      uint stride;


      this(int[] array, uint rows, uint cols, uint start=0, uint
stride=uint.max)
      {
          this.array = array;
          this.rows = rows;
          this.cols = cols;
          this.start = start;
          this.stride = stride == uint.max ? cols : stride;
      }


      uint opDollar(uint dim)()
      {
          static assert(dim <= 1);
          static if (dim == 0) return rows;
          else return cols;
      }

      slice opSlice(uint from, uint to)
      {
          return slice(from, to-from);
      }


      int opIndex(uint r, uint c) {
          return array[start + r*stride + c];
      }

//    int[] opIndex(slice rs, uint c) {
//        // ...
//    }

//    int[] opIndex(uint r, slice cs) {
//        // ...
//    }

      Example opIndex(slice rs, slice cs)
      {
          uint r = rs.size;
          uint c = cs.size;
          uint s = start + rs.start*stride + cs.start;

          return Example(array, r, c, s, stride);
      }

}



int main() {


      auto m = Example([  11, 12, 13, 14,
                          21, 22, 23, 24,
                          31, 32, 33, 34,
                          41, 42, 43, 44,
                          51, 52, 53, 54 ],
                      5, 4);

      assert (m[3, 2] == 43);


      auto m2 = m[slice(2, 3), slice(2, 2)];  // <- this is the
construct I use in C++
      assert (m2[1, 0] == 43);
      assert (m2.rows == 3 && m2.cols == 2);

      // m3 should refer to the same slice as m2
      auto m3 = m[2..5, 2..4];   // <- compiler syntax error is 
here
      assert (m3[1, 0] == 43);
      assert (m3.rows == 3 && m3.cols == 2);

      return 0;

}

the compiler kicks me out with a syntax error:
Error: found ',' when expecting ']'
Error: semicolon expected following auto declaration, not '2'
Error: found '..' when expecting ';' following statement
Error: found ']' when expecting ';' following statement


Have I done something wrong?
Or may be has the documentation been quicker than the compiler
implementation?
Or a compiler bug?


thanks
Rémi