Variadic grouping

[John Colvin]

On Monday, 29 July 2013 at 13:23:23 UTC, JS wrote:
> Sometimes it's nice to be able to have groups of variadic 
> parameters:
>
> template t(T1..., T2...)
>
> ...
>
> t!(a, b, c; d, e, f);
>
> so that a,b,c are for T1 and d,e,f are for T2.
>
> This can be done by making a symbol and breaking up a single 
> variadic but is messy.
>
> I doubt such a feature will ever get added but who knows...

I was initially unimpressed, but after some recent work I would 
really like this feature. I have been using
   struct Group(T...)
   {
       alias Ungroup = T;
   }
but, useful as it is, this feels like something that should have 
some sugar on it.

   template A(T0 ..., T1 ...)
   {
   // use T0 & T1
   }

   A!(int, long, double; Point, int)

is so much nicer than

   template A(T0, T1)
   if(isGroup!T0 && isGroup!T1)
   {
       alias t0 = T0.Ungroup;
       alias t1 = T1.Ungroup;

       //use t0 && t1
   }

   A!(Group!(int, long, double), Group!(Point, int))