On 08/05/2013 11:45 AM, kdmult wrote:
> Hi,
>
> I would like to use a tuple template parameter in the default value of
> another template parameter in the same class declaration as follows.
>
> class A(P...) {}
>
> class B(R = A!P, P...) {}
>
> P... should be rightmost, so how can I use it in the preceding parameter?
>
> Thanks.
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
