• via Digitalmars-d-bugs (45/45) Sep 24 2016 https://issues.dlang.org/show_bug.cgi?id=16537

via Digitalmars-d-bugs <digitalmars-d-bugs puremagic.com> writes:

https://issues.dlang.org/show_bug.cgi?id=16537

          Issue ID: 16537
           Summary: [ndslice] cannot use slice as in function parameter,
                    error on opIndex
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: major
          Priority: P1
         Component: phobos
          Assignee: nobody puremagic.com
          Reporter: clumsycodemonkey gmail.com

The operators of an ndslice object don't handle const very well, which makes it
difficult to write functions that take slices as in parameters. See sum slice
functions below, the one that takes in parameters requires casts to work!

--------------------------------
alias MyMatrix = Slice!(2,double*);

MyMatrix sumSlice(MyMatrix a, MyMatrix b)
{
  assert(a.shape == b.shape);

  auto rows = a.shape[0];
  auto cols = a.shape[1];
  auto result = (new double[a.elementsCount]).sliced(rows, cols);

  foreach(r; 0..rows) foreach(c; 0..cols) result[r,c] = a[r,c] + b[r,c];

  return result;
}

MyMatrix sumSlice2(in MyMatrix a, in MyMatrix b)
{
  assert(a.shape == b.shape);

  auto rows = a.shape[0];
  auto cols = a.shape[1];
  auto result = (new double[a.elementsCount]).sliced(rows, cols);

  foreach(r; 0..rows) 
    foreach(c; 0..cols) 
      // Casts required to compile!!
      result[r,c] = (cast()a)[r,c] + (cast()b)[r,c];

  return result;
}
--------------------------------

I was using ndslice as a matrix and trying to write functions to do matrix
factorizations where I did not destroy the original matrix. So it makes sense
to be able to use opIndex in this way.

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