Extracting template parameters

[Dan]

On Tuesday, 6 November 2012 at 15:20:43 UTC, Joseph Rushton 
Wakeling wrote:

> 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 ...

Would something like this be what you are after?

import std.stdio;

struct Foo(_T1, _T2, _T3)
{
   alias _T1 T1;
   alias _T2 T2;
   alias _T2 T3;
}

struct Bar(_T1, _T2, _T3)
{
   alias _T1 T1;
   alias _T2 T2;
   alias _T2 T3;
}

auto fooToBar(F)(F f) {
   Bar!(F.T1, F.T2, F.T3) b;
   writeln("I have a ", typeid(typeof(b)));
   return b;
}
void main() {
   alias Foo!(int, string, char) X;
   X x;
   fooToBar(x);
}

Thanks
Dan