Polymorphism in regular variadic function

[Jarrett Billingsley]

"Bill Baxter" <wbaxter at gmail.com> wrote in message 
news:el2iq4$2gb3$1 at digitaldaemon.com...
> Is there any way to check if an argument is type T or anything derived 
> from it using the TypeInfo?
>
> Basically I want this:
>
> class Foo { int x = 3; }
> class Bar : Foo { long y = 4; }
>
> void printargs(...)
> {
>     printf("%d arguments\n", _arguments.length);
>     for (int i = 0; i < _arguments.length; i++)
>     {   _arguments[i].print();
>
>         // Want to accept Foo or anything derived from Foo here!
> if (_arguments[i] == typeid(Foo))
> {
>     Foo f = *cast(Foo*)_argptr;
>     _argptr += Foo.sizeof;
>     printf("\t%p\n", f);
> }
> else
>     assert(0);
>     }
> }
>
>
> --bb

Heheh.. I did something like:

TypeInfo ti = _arguments[i];
TypeInfo_Class tic = cast(TypeInfo_Class)ti;

if(tic)
{
    ClassInfo ci = tic.info;

    for( ; ci !is null; ci = ci.base)
        if(ci == Foo.classinfo)
        {
            // it's derived, do what you will
        }

    if(ci is null)
    {
        // we got to the base without finding Foo,
        // it's not derived from Foo
    }
}

I wonder if there's any way to take advantage of the internal casting 
functions (which are used whenever you do a dynamic downcast).  Well, now 
that I think about it, you might be able to replace the above condition 
with:

if(tic)
{
    Object o = va_arg!(Object)(_argptr);
    Foo f = cast(Foo)o;

    if(f !is null)
    {
        // it's a Foo
    }
}

Which .. would probably work.  Give it a shot.