[boost] Re: [preprocessor] BOOST_PP_IS_UNARY for Borland

From: Daniel James (daniel_at_[hidden])
Date: 2004-08-16 04:17:25

Paul Mensonides wrote:
> I see no problem with adding the functionality, but the macros still cannot
> safely be made public.  On other compilers (besides Borland), their use causes
> stability problems.  Using something like the above doesn't help (it would
> actually be slightly worse) because of the reliance on intermediates in the
> argument--which requires that expansion order proceed as it should (which is not
> the case on some preprocessors).

That's a shame. I find it very useful.

>>Also, with a full working BOOST_PP_IS_UNARY, I 
>>think it should be possible to make BOOST_PP_SEQ_NIL act as 
>>an empty sequence, if I write a patch to do that would it be accepted?
> 
> It is already possible because the identifier is known.

I should have realised that, since that's how lists work.

> Lack of a nil sequences
> (until we get placemarkers) was a conscience decision.  An important property of
> sequences is the ability to directly append.  By definition, if A and B are both
> sequences, then A B is also a sequence.

That makes sense. I guess my version isn't that useful then. But, it's a 
nice trick and I can use it in my own stuff, which will probably never 
work on preprocessors where BOOST_PP_IS_UNARY is unstable.

thanks,

Daniel