Understanding Templates: why can't anybody do it?

[Nick Sabalausky]

"H. S. Teoh" <hsteoh at quickfur.ath.cx> wrote in message 
news:mailman.834.1332023905.4860.digitalmars-d at puremagic.com...
>
> (Not to mention, D templates can do some stuff that no OO can hope to
> attain. But it goes both ways. Templates can't do runtime polymorphism
> either.)
>

Combined with compile-time reflection, I'm sure they could be used to create 
a runtime polymorphism tool, even multiple dispatch. Like I mentioned 
recently in a seperate thread, you'd just need to use templates/ctfe to 
automate/genericize this:

void singleDispatch(Object o)
{
    if(auto derived = cast(DerivedClassA)o)
        derived.foo();
    else if(auto derived = cast(DerivedClassB)o)
        derived.foo();
    else if(auto derived = cast(DerivedClassC)o)
        derived.foo();
    //etc...
}

Although I guess *technically* you're still relying on OO polymorphism (in 
the form of downcasting) to achieve this. OTOH, you could still base it on 
Variant or Algebraic instead of (or in addition to) Object. Then you'd have 
built runtime polymorphism out of templates (among other things) without 
relying on OO.