Re: Formal Review of std.range.ndslice

[Ilya via Digitalmars-d]

On Friday, 11 December 2015 at 22:56:15 UTC, Ilya wrote:

On Friday, 11 December 2015 at 19:31:14 UTC, Stefan Frijters wrote:

Today I've made an abortive attempt at replacing my code's [1] dependence on unstd.multidimarray [2] with ndslice. I'm guessing it's just me being stupid, but could anyone supply with some hints on how to do the conversion with a minimum of fuss?

Basically I have an N-dimensional array (N is known at compile time) of type T wrapped in a struct to carry some additional information. I then address it using size_t[N] fixed-size arrays, and loop over it a lot with foreach, which also uses size_t[N] as index.

So it looks something like this:

struct Field(T, uint N) {

  alias arr this;

MultidimArray!(T, N) arr; // is there any way to supply the correct type here with ndslice? I cannot use auto, right?

    Slice!(N, T*) arr;

  this (in size_t[N] lengths) {
    arr = multidimArray!T(lengths);

      // compute length
      // more flexible construtors would be added after
      // allocatrs support for ndslice
      size_t len = 1;
      foreach(l; lengths)
         len *= l;

      arr = new T[len].sliced(lengths);

  }
}
and then things like

foreach(immutable p, ref pop; someField) {
  pop = foo(someOtherField[bar(p)]);
  ...
}

   std.experimental.ndslice.selection: indexSlice, byElement;

   foreach(p; someField.shape.indexSlice.byElement) {
          someField[p] = foo(someOtherField[bar(p)]);
          ...
   }

faster version:

std.experimental.ndslice.selection: byElement;

for(auto r = someField.arr.byEleemnt; r.popFront) {
        r.front = foo(someOtherField[bar(r.index)]);
        ...
}

where p is of type size_t[N].

Ilya