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