Initializing static array with contents of (static and dynamic) arrays

[Johannes Loher via Digitalmars-d-learn]

Am 05.07.2016 um 17:12 schrieb Johannes Loher:
> Am 05.07.2016 um 16:39 schrieb Rene Zwanenburg:
>> On Tuesday, 5 July 2016 at 12:34:20 UTC, Johannes Loher wrote:
>>> I tried this, but it does not work correctly with slices.
>>
>> The length of a slice is a runtime value, which is why it can't be used
>> to set static array size. What were you trying to achieve? Avoid copying
>> the input arrays, or accepting any slice?
>>
>> In case of the first, you can put ref in front of the Args:
>> auto combineArrays(Args...)(ref Args args)
>>
>> The second case will be a bit harder to solve nicely..
> 
> I would like to be able, to accept any slice. In the example in my first
> post, I need this for key[0..16] and key[16..$] (which are slices).
> Strangely enough, the solution I am leaning towards at the moment also
> uses length, but it does work for slices of static arrays (i.e. key[0..16]):
> 
> template expand(alias A)
> {
>     auto ref M(alias I)() @property { return A[I]; }
>     mixin(q{alias expand = TypeTuple!(}
>         ~ iota(A.length).map!(a => "M!" ~ a.to!string).join(",")
>         ~ q{);});
> }
> 
> ubyte[64] buf = [expand!sigma0,
>                  expand!key[0..16],
>                  expand!sigma1,
>                  expand!n,
>                  expand!sigma2,
>                  expand!key[16..$],
>                  expand!sigma3];
> 
> I suppose this is because the length of those slices is actually known
> at copiletime, but it looks a bit strange to me...
> 
> I was trying to write another template that takes several arrays and
> expands all of them:
> 
> template expand(Args...)
> {
>     mixin(q{alias expand = TypeTuple!(}
>         ~ iota(Args.length).map!(a => "expand!(Args[" ~ a.to!string ~
> "])").join(",")
>         ~ q{);});
> }
> 
> It works for static arrays, but not for slices, because the template
> parameters are not alias parameters, so the length is then not "known"
> at compile time (at least that's what I think why it fails). Is there a
> way to specify variadic templates taking any number of alias template
> parameters?
> 

Well, I just realized my method does not work in the case that I want to
use expand on static arrays, which are returned from template functions...