Appending static arrays

[Nordlöw via Digitalmars-d-learn]

On Monday, 17 July 2017 at 20:10:31 UTC, H. S. Teoh wrote:
> On Mon, Jul 17, 2017 at 08:11:03PM +0000, Nordlöw via 
> Digitalmars-d-learn wrote: [...]
>> Does this have a place in Phobos?
>
> Never know till you try. :-D
>
>
>> If so,
>> 
>> - under what name: append, concat or cat?
>
> I'd vote for concat.
>
>
>> - where: std.algorithm or std.array?
>
> std.array, IMO, since it's specific to static arrays.
>
>
> T

Made some adjustments with working unittest and put it up on

https://github.com/nordlow/phobos-next/blob/master/src/algorithm_ex.d#L2467

I had to special-case foreach body for `i == 0` since 
`sumOfLengths` couldn't instantiate with empty tuple `()`.

Further, should `concat` support `CommonType`? That is, should

     int[2] x = [1, 2];
     const double[2] y = [3, 4];
     auto z = concat(x, y);
     static assert(is(typeof(z) == double[4]));

be allowed?