tuple parameter fwd

[kdmult]

On Tuesday, 6 August 2013 at 09:53:33 UTC, Ali Çehreli wrote:
> Do you mean that when P[0] is already an instance of A, then R 
> should be P[0]. Otherwise, R should be A!P? If so, the 
> following works:
>
> class A(P...)
> {
>     pragma(msg, "\nA: " ~ P.stringof);
> }
>
> class BImpl(R, P...)
> {
>     pragma(msg, "R: " ~ R.stringof ~ ", P: " ~ P.stringof);
> }
>
> template B(P...)
> {
>     static if (is (P[0] == A!U, U)) {
>         /* The first type is already an A instance. Accept the 
> types as is. */
>         alias B = BImpl!P;
>
>     } else {
>         /* The first type is not an A instance. Inject one. */
>         alias B = BImpl!(A!P, P);
>     }
> }
>
> void main()
> {
>     auto b0 = new B!(int, double, char);
>     auto b1 = new B!(A!long, int, double);
> }
>
> Ali

Great! Thanks Ali.