is(T t == U!n, U, int n)

[Simen Kjærås]

On Wednesday, 13 June 2018 at 09:41:45 UTC, Luís Marques wrote:

> ...why can't I generalize it to match U!n, for some U, int n?
>
>     template X(T)
>     {
>         static if(is(T t == U!n, U, int n))

U needs to be alias U, since S is not a type, but a template. 
This works:

template X(T)
{
     static if(is(T t == U!n, alias U, int n))
     {
         static if(n == 0)
             alias X = AliasSeq!();
         else
             alias X = U!0;
     }
     else
     {
         static assert(0);
     }
}

class S(int n) { }

pragma(msg, X!(S!3));

Also, you might want to consider the Learn forum for these kinds 
of questions in the future. :)

--
   Simen