dupping to allow vector operation?

[via Digitalmars-d-learn]

On Thursday, 9 October 2014 at 11:29:14 UTC, bearophile wrote:
> Observe:
>
> void main() {
>      int[3] a1 = [1, 3, 6];
>      int[]  a2 = a1[] * 3;       // line 3, Error
>      int[]  a3 = a1.dup[] *= 3;  // line 4, OK?
>      int[]  a4 = (a1[] * 3).dup; // line 5, Error
> }
>
>
> Currently the operation in line 4 is accepted:
>
> test.d(3,17): Error: array operation a1[] * 3 without 
> destination memory not allowed
> test.d(5,18): Error: array operation a1[] * 3 without 
> destination memory not allowed
>
> Is it a good idea to support something like line 5?

It's equivalent to:

     int[] tmp = a1[] * 3;
     int[] a4 = tmp.dup;

The first part is of course identical to line 3, so this should 
be an error, too. Normal rules for evaluation order require `a1[] 
* 3` to be evaluated before `(...).dup`, so where is it supposed 
to store the intermediate result?