Re: too many warnings from Bison CVS for Pike

[Akim Demaille]

Le 21 févr. 06 à 19:34, Joel E. Denny a écrit :

> On Tue, 21 Feb 2006, Akim Demaille wrote:
>
> > People, like me
> > years ago, know that you can have C code manipulate C++ structures
> > properly as long as they are PODs.  Trying to use non PODs in
> > yacc.c is not supported, that's the role of lalr1.cc.  I'll
> > write a piece of documentation about this.
>
> Section `10.1.2 C++ Semantic Values' explains that only *pointers* to
> non-POD types can be used in %union for "lalr1.cc" and that % 
> destructor is
> needed to prevent memory leaks.

That's because we are using a union underneath.  So we inherit
the same limitations.

> I've been doing the same for "yacc.c".
> I've talked to others who do this as well, but I've not searched for
> online references to this usage.  If this usage is somehow an abuse of
> "yacc.c", a note about it might be helpful in the documentation.
>
> If this usage is fine, then I wonder how "lalr1.cc" supports non- 
> POD types
> more than "yacc.c".  A footnote in the same section says that
> `pseudo-unions' may alleviate this need for pointers in the  
> future.  So,
> are you referring to future plans rather than current support?

Yes.  Supporting non-PODs is really tough to do properly.  We need
something like Boost's variants.

http://www.boost.org/doc/html/variant.html

The portability issues are a bit frightening :(  If you care to read the
excellent material from A. Alexandrescu, you'll see what I mean.
Fortunately we need something less advanced than this, so it should be
really doable, but does require some time.

http://www.cuj.com/documents/s=7984/cujcexp2004alexandr/
http://www.cuj.com/documents/s=7982/cujcexp2006alexandr/
http://www.cuj.com/documents/s=7980/cujcexp2008alexandr/