[boost] [preprocessor] seq/size.hpp BOOST_PP_SEQ_SIZE MSVC empty list warning

Subject: [boost] [preprocessor] seq/size.hpp BOOST_PP_SEQ_SIZE MSVC empty list warning
From: damien benoist (damien_benoist_at_[hidden])
Date: 2011-04-19 11:29:10

Hello,

It seems that BOOST_PP_SEQ_SIZE generates a warning
with empty sequences under MSVC (vs 2010/boost 1.46.1).
The same call works with gcc.
The tests are available below.

I've also put a patch but:
- I'm really not sure of it (I have never been as
far with preproceesor as in boost/preprocesor/)
- I only tested it with BOOST_PP_CONFIG_MSVC
(it should also be tested with BOOST_PP_CONFIG_EDG)

And anyway this warning will likely appear with all
macros manipulating sequences.
Should this warning just be ignored or disabled
with MSVC?

More general question:

I'm discovering boost.
I'm really impressed by the macros in boost/preprocessor.
It makes a lot of things possible.
But it provides features the preprocessor was not
meant for. For that, it uses a lot of tricks.

How portable is it?
How many architectures is it known to work/not work with?
Can we be confident that it should work with any preprocessor?

Thanks for your help.



$ cat lstsz2.h
#include "boost/preprocessor/seq/size.hpp"

#define lst0
#define lst1 (a)
#define lst2 (a)(b)
#define lst3 (a)(b)(c)

BOOST_PP_SEQ_SIZE(lst0)
BOOST_PP_SEQ_SIZE(lst1)
BOOST_PP_SEQ_SIZE(lst2)
BOOST_PP_SEQ_SIZE(lst3)
$ cpp -I ~/wh/softs/boost/1.46.1 < lstsz2.h
...
0
1
2
3
$ cl -I `cygpath -d "$HOME/wh/softs/boost/1.46.1"` /E lstsz2.h
...
0
1
2
3
lstsz2.h(8) : warning C4003: not enough actual parameters for macro  'BOOST_PP_SEQ_SIZE_I'



$ diff -u 1.46.1/boost/preprocessor/seq/size.hpp.old 1.46.1/boost/preprocessor/seq/size.hpp
--- 1.46.1/boost/preprocessor/seq/size.hpp.old  2005-06-21 09:55:15.000000000 +0200
+++ 1.46.1/boost/preprocessor/seq/size.hpp      2011-04-19 14:42:02.218750000 +0200
@@ -13,6 +13,7 @@
# define BOOST_PREPROCESSOR_SEQ_SIZE_HPP
#
# include <boost/preprocessor/cat.hpp>
+# include <boost/preprocessor/empty.hpp>
# include <boost/preprocessor/config/config.hpp>
# include <boost/preprocessor/tuple/eat.hpp>
#
@@ -21,7 +22,7 @@
#    define BOOST_PP_SEQ_SIZE_I(par) BOOST_PP_SEQ_SIZE_II ## par
#    define BOOST_PP_SEQ_SIZE_II(seq) BOOST_PP_CAT(BOOST_PP_SEQ_SIZE_, BOOST_PP_SEQ_SIZE_0 ## seq)
# elif BOOST_PP_CONFIG_FLAGS() & BOOST_PP_CONFIG_EDG() || BOOST_PP_CONFIG_FLAGS() & BOOST_PP_CONFIG_MSVC()
-#    define BOOST_PP_SEQ_SIZE(seq) BOOST_PP_SEQ_SIZE_I(seq)
+#    define BOOST_PP_SEQ_SIZE(seq) BOOST_PP_SEQ_SIZE_I(seq BOOST_PP_EMPTY())
#    define BOOST_PP_SEQ_SIZE_I(seq) BOOST_PP_CAT(BOOST_PP_SEQ_SIZE_, BOOST_PP_SEQ_SIZE_0 seq)
# elif defined(__IBMC__) || defined(__IBMCPP__)
#    define BOOST_PP_SEQ_SIZE(seq) BOOST_PP_CAT(BOOST_PP_SEQ_SIZE_, BOOST_PP_CAT(BOOST_PP_SEQ_SIZE_0, seq))