Re: %union errors that shouldn't be there

[Hans Aberg]

At 14:56 +0100 2005/03/25, Laurence Finston wrote:
>  > This discussion is very confusing, because it mixes two topics:
> >  Extending C++, and what is appropriate for Bison.
>
> This is just my opinion, but I don't think adding type information to `union'
> would be in the spirit of C.  If this feature were added, the first thing I'd
> do would be to look for a way to turn it off.

It would be in the spirit of C++. :-)

>  > As for the latter
> >  question, one would have to give iyt a different name that %union.
> >  But with the %typed and other features suggested here (%define),
> >  that would not be a problem.
>
> No, but what would be the advantage over something like the following?
>
> struct Yystype_Struct
> {
>    unsigned short type;
>
>    void* object;
>
> };

With unions, one wants to avoid dynamic allocations. Each dynamic 
allocation takes several tens, sometimes, hundreds of cycles.

> I don't understand why you would want to use `union' at all.  Of course,
> what's appropriate for Bison is up to the maintainers and developers, so I'll
> stay out of that one.   From my point of view as a user, it's perfectly simple
> to use `void*' in `%union', and I suspect that it will be perfectly simple to
> use it as `YYSTYPE' (I haven't tried it yet).
> So what problem are you trying to solve?

Unions are faster than dynamic allocations, and in the past, it was 
important that they take little space. One example where I have used 
it is a series of function pointer of different type.
--
  Hans Aberg