Re: %destructor feedback

[Joel E. Denny]

On Sun, 23 Oct 2005, Frank Heckenbach wrote:

> Joel E. Denny wrote:
>
> > YYUSE is really a no-op.  In other words:
> >
> >    $5;
> >
> > is nearly equivalent to:
> >
> >    YYUSE($5);
> >
> > The first would be compatible with any bison version.
>
> ... and would likely produce a compiler-warning. Exchanging a Bison
> warning for a compiler warning doesn't really gain much.

I clearly didn't think that one through.  Thanks.  I'm not sure why I left 
that in the email given how much more readable it would be for the user to 
write his own macro inside a #ifndef.

> Basically yes. (Though the recent development of YYUSE and your
> following comment seem to show that it isn't quite that easy to
> write a general-purpose warning-free YYUSE ...)

I guess YYUSE was really intended to suppress warnings from the C 
compiler, which may be tricky as you suggest.  Our warnings would come 
from bison, so try this instead:

  #define YYBISON_USE( param ) /* Empty. */

Example usage:

  YYBISON_USE( $1 )
  YYBISON_USE(( $1, $2, $3 ))

Thus, bison sees the $1, $2, and $3, but the C compiler sees nothing after 
preprocessing.

Again, the user himself could write this macro in a #ifndef for 
compatibility with prior bison releases.

> > > OTOH, making the warning optional shouldn't take more than a global
> > > flag in Bison unless I'm missing something.
> >
> > If someone wants to implement the global flag, I won't argue.  I just
> > worry that...
>
> I guess I could write those few lines, if that's the main problem. ;-)

I wasn't trying to argue that it would be difficult to implement the flag. 
I meant to say that I had a small misgiving about the flag that I thought 
ought to be considered, but if anyone proposes a patch to implement the 
flag, I for one won't bother to argue against it.

Joel