foreach(i,ref val; ndim_arr)??

[9il via Digitalmars-d-learn]

On Tuesday, 10 May 2016 at 15:18:50 UTC, ZombineDev wrote:
> On Tuesday, 10 May 2016 at 10:21:30 UTC, ZombineDev wrote:
>
> (You can try it at: https://dpaste.dzfl.pl/c0327f067fca)
>
> import std.array : array;
> import std.experimental.ndslice : byElement, indexSlice, sliced;
> import std.range : iota, lockstep, zip;
> import std.stdio : writefln;
>
> void main()
> {
>     // needs .array for ref (lvalue) access
>     // (iota offers only rvalues)
>     auto slice = iota(2 * 3 * 4).array.sliced(2, 3, 4);
>
>     auto indexed_range = lockstep(
>         slice.shape.indexSlice.byElement(),
>         slice.byElement()
>     );
>
>     writefln("%s", slice);
>
>     foreach (idx, ref elem; indexed_range)
>         writefln("Element at %s = %s", idx, ++elem);
> }
>

The code above is slow because it calculates index using multiple 
assembler ops.

Following would be faster:

for(auto elems = slice.byElement; !elems.empty; elems.popFront)
{
     size_t[2] index = elems.index;
     elems.front = index[0] * 10 + index[1] * 3;
}

For really fast code just use multiple foreach loops:

foreach(i; matrix.length)
{
     auto row = matrix[i]; // optional
     foreach(j; matrix.length!1)
     {
         ...
     }
}