How to expand an expression along with a parameter tuple?

[TommiT]

On Monday, 17 June 2013 at 13:59:34 UTC, Artur Skawina wrote:
>
> Another solution would be to have the following hidden in some 
> lib:
>
>    struct _ForEach(alias MAP, TS...) {
>       NTup!(TS.length, typeof(MAP(TS[0].init))) tuple;
>
>       this(TS values) {
>          foreach (i, ref v; values)
>             tuple[i] = MAP(v);
>       }
>    }
>
>    auto ForEach(alias MAP, TS...)(TS ts) {
>       return _ForEach!(MAP, TS)(ts);
>    }
> 
> Then 'bar' becomes just:
>
>    void bar(T...)(T values) {
>       foo(ForEach!(a=>arr[a]*10)(values).tuple);
>    }
>
> Yes, this is not as concise as '...' would be. But, with a bit 
> more
> tuple support in the language, the '.tuple' part wouldn't be
> necessary, and then it's just
>
>       foo(ForEach!(a=>arr[a]*10)(values));
> vs
>       foo((arr[values] * 10)...);
>
> artur

Now, this is pretty cool. But I wonder a couple of things:
1) What kind of an impact does this have on compilation times 
compared to having this new ellipsis syntax which would allow the 
compiler to do a simple rewrite.
2) I wonder if the compiler can optimize that _ForEach struct 
away.