Extracting template parameters

[Joseph Rushton Wakeling]

On 11/06/2012 04:20 PM, Joseph Rushton Wakeling wrote:
> The use-case I'm thinking of is a function something like this (somewhat
> pseudo-code-y):
>
>      auto fooToBar(FooInstance f)
>      {
>          Bar!(f.T1, f.T2, f.T3) b;
>          // set values etc.
>          return b;
>      }
>
> Of course the f.T1 notation is my fiction, but it gives the idea of what is
> needed -- is there a means to extract and use template parameters in this way? I
> assume something from std.traits but it's not entirely clear what or how ...

Ideally this solution would work for non-identical lists of template parameters. 
  E.g. for

     Foo(T1, T2, T3, T4)
     {
     }

     Bar(X1, X2)
     {
     }

I'd like to be able to instantiate something like: Bar!(f.T2, f.T4) [again, 
using my fictional notation].