Unwrap variadic template into vararg of pointers of the same types

[wjoe]

On Friday, 8 July 2022 at 12:20:13 UTC, ryuukk_ wrote:
> I'm not sure how to phrase it so it'll try with code
>
> I have this piece of code that i would like to improve, right 
> now i have to create bunch of duplicates
>
> ```D
>     void view_it(A, B)(void function(entity_t, A*, B*) cb)
>     {
>         foreach(it, e; view!(Includes!(A, B)))
>         {
>             auto a = it.get!(A)(e);
>             auto b = it.get!(B)(e);
>             cb(e, a, b);
>         }
>     }
> ```
>
> The problem when i try to introduce variadic template, is i 
> can't seem to understand how to unwrap the parameter as pointer 
> type T -> T*
>
>
> ```D
> struct Includes(Args...) { alias args = Args; }
>
> void view_it(Includes)(void function(entity_t, Includes.args* ) 
> cb)
> {
>     // do stuff
> }
>
> ```
>
> I get the following:
>
> ```Error: cannot have pointer to `(EEntityRemoved)```
>
> Anyone got an idea?
>
> Thanks!

I suppose you could do something like this:

```d
template Includes(Args...)
{
    template Recurse(Arg...)
    {
       import std.meta: AliasSeq;
       static if (1 == Arg.length)
         alias Recurse = AliasSeq!(Arg[0]*);
       else
         alias Recurse = AliasSeq!(Arg[0]*, Recurse!(Arg[0..$]);
    }

    alias Includes = Includes!(Args);
}
void view_it(Args...)(void function(entity_t, Includes!(Args) )
```