how can i use the derive-hierarchy at runtime for typechecking?

[Jarrett Billingsley]

"Chris Nicholson-Sauls" <ibisbasenji at gmail.com> wrote in message 
news:fcupko$kh7$2 at digitalmars.com...

> void ifIs (S, T) (S obj, void delegate(T) dg) {
>   if (auto casted = cast(T) obj) dg(casted);
> }

Or you could skip Downs' confusing way of writing code entirely ( ;) ) and 
just use:

if(auto b = cast(B)foo)
{
    // do stuff with b
}