Re: [boost] For Boost PP: IF_NONEMPTY(), IS_NONEMPTY

Subject: Re: [boost] For Boost PP: IF_NONEMPTY(), IS_NONEMPTY
From: Daniel Santos (danielfsantos_at_[hidden])
Date: 2012-05-09 16:21:02

On 05/08/2012 12:12 PM, Daniel James wrote:
> There's BOOST_PP_IS_EMPTY in
> <boost/preprocessor/facilities/is_empty.hpp> although it isn't
> publicized as it won't work on some preprocessors. I haven't look
> closely enough to see how it compares.
Cool, thanks!  This one really does a lot of compiler checks and mine is
gcc-specific.  I came up with a much better variation (below).  As far
as the standards, I think an empty pre-processor parameter is only
well-formed in C++03 or 11 and in C99 and later.

#define __JUNK junk,
#define _iff_empty(arg1_or_junk, t, f) __iff_empty(arg1_or_junk, f, t)
#define __iff_empty(__ignored1, __ignored2, result, ...) result
#define IFF_EMPTY(test, t, f) _iff_empty(__JUNK##test, t, f)

#define IS_EMPTY(test)    IFF_EMPTY(test, 1, 0)

While this works in gcc, it doesn't deal with any compiler quirks &
differences, sorry.
Daniel