[boost] Re: Re: Novelty: automatically assigning unique integraltype ids

From: Jonathan Turkanis (technews_at_[hidden])
Date: 2004-12-06 15:58:32

"Jody Hagins" <jody-boost-011304_at_[hidden]> wrote in message
news:20041206153207.0dd11478.jody-boost-011304_at_atdesk.com...
> On Sat, 4 Dec 2004 23:44:46 -0700
> "Jonathan Turkanis" <technews_at_[hidden]> wrote:
>
>
> > You don't need typeid -- you can just do:
> >
> >    template<typename T>
> >    struct unique_id_holder {
> >        static char val;
> >    };
> >
> >    template<typename T>
> >    char unique_id_holder::val;
> >
> >    template<typename T>
> >    int unique_id()
> >    {
> >        return reinterpret_cast<int>(&unique_id_holder::val);
> >    }
>
>
> For "better" portability, you should make that "int" a "long."

True. Daryle mentioned the problems about the size of integral types, and I was
taking it for granted. The reason it doesn't matter much is that the
applications which could benifit from a compile-time type id could do just as
well if the id were split into several components.

> Specifically, each of the above will get a
> different ID when calling unique_id<T>() with modifiers and references,
> but they will get the "same" std::type_info for those calls.

Yes, good point. It would be nice, for several purposes, if typeid were less
forgetful.

Jonathan