Why does it expand to BOOST_VERSION_NUMBER_AVAILABLE?

[vinipsmaker]

Boost.Predef macros (e.g. BOOST_OS_WINDOWS) expand to BOOST_VERSION_NUMBER_AVAILABLE instead of 1 or 0. Why is that?

By expanding to BOOST_VERSION_NUMBER_AVAILABLE I can't use these macros in Boost.PP. For instance, I recently had to use code like:

BOOST_PP_IF(
    BOOST_OS_UNIX,
    lua_pushcfunction(L, tcp_socket_assign),
    lua_pushcfunction(L, throw_enosys));

But it failed to compile because BOOST_OS_UNIX doesn't expand to 1 or 0. Instead, it expands to a complex expression that can't be used in preprocessor metaprogramming.

Could we offer BOOST_OS_UNIX10 (and the equivalent to other macros as well) that expand to 1 or 0 instead of a complex expression? Or, alternatively, modify these macros to expand to 1 or 0 already?

[grafikrobot]

Does using BOOST_OS_UNIX() or BOOST_PP_EXPAND(BOOST_OS_UNIX) work?

[vinipsmaker]

Does using BOOST_OS_UNIX() or BOOST_PP_EXPAND(BOOST_OS_UNIX) work?

No.

The output for BOOST_PP_IF(BOOST_PP_EXPAND(BOOST_OS_UNIX), a, b) is:

BOOST_PP_IIF_BOOST_PP_BOOL_BOOST_PP_EXPAND(( (((0)%100)*10000000) + (((0)%100)*100000) + ((1)%100000) ))(a, b)

If BOOST_PP_IF(BOOST_PP_EXPAND(BOOST_OS_UNIX), a, b) is given as input.