Per-type %destructor?

[Bart Samwel]

Hi everybody,

I've just picked up bison 2.1, and I read in the manual that feedback on 
the %destructor feature was wanted. I do have one issue with the way it 
is implemented, and I didn't find any discussions in the archives that 
mentioned this, so here I am to report. If this has already been 
resolved or rejected earlier, please forgive my ignorance. :-)

My issue with the 2.1 %destructor feature is that destructors are only 
specifiable on a per-symbol basis, while I would like to specify them 
per *type*. I am building a parser that simply generates an AST, using 
something like this:

%union {
   Element *elem;
   SomeOtherType *blah;
}

%type <elem> almost all of my symbols go here
%type <blah> a couple of symbols go here

All of the elem types are "owned" by their tokens, while the blah types 
are *not* the owners of the SomeOtherType objects that the blah value 
points to. So I would like to specify something like:

%destructor <elem> { delete $$; }

And leave the <blah>-typed symbols without a destructor. But no, I 
apparently have to specify:

%destructor { delete $$; } almost all of my symbols go here

So, I have to redundantly specify every symbol that has type <elem>. If 
I make one mistake in the list, I'm screwed:

1. If I mistakenly include a blah-typed symbol, the destructor will 
delete the SomeOtherType that the symbol didn't own. And it will compile 
cleanly. :-(

2. If I mistakenly forget an elem-typed symbol (for instance because I 
added a new one), then its destructor won't get called, and I have a 
memory leak.

So, is there any chance that a type-wide %destructor specification will 
appear in bison? Without it, I'm afraid that I'm not going to use the 
feature, as I'm quite sure that someone on my team will forget to keep 
the lists in sync at some point. :-) Thanks in advance for your thoughts.

Cheers,
Bart