# Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world.

### boost/vmd/is_empty.hpp


//  (C) Copyright Edward Diener 2011-2015,2019
//  Use, modification and distribution are subject to the Boost Software License,
//  Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at

#if !defined(BOOST_VMD_IS_EMPTY_HPP)
#define BOOST_VMD_IS_EMPTY_HPP

#include <boost/vmd/detail/setup.hpp>

#include <boost/preprocessor/punctuation/is_begin_parens.hpp>
#include <boost/vmd/detail/is_empty.hpp>

/*

The succeeding comments in this file are in doxygen format.

*/

/** \file
*/

/** \def BOOST_VMD_IS_EMPTY(...)

\brief Tests whether its input is empty or not.

The macro checks to see if the input is empty or not.
It returns 1 if the input is empty, else returns 0.

The macro is a variadic macro taking any input.
For the VC++8 compiler (VS2005) the macro takes a single parameter of input to check.

For all levels of C++ prior to C++20 the macro is not perfect,
and can not be so. The problem area is if the input to be
checked is a function-like macro name, in which case either
a compiler error can result or a false result can occur.

For C++20, with its support for the new __VA_OPT__ preprocessor
construct, the macro will always work correctly no matter what
the variadic input, and is therefore 100% reliable.

This macro is a replacement, using variadic macro support,
for the undocumented macro BOOST_PP_IS_EMPTY in the Boost
PP library. The code is taken from a posting by Paul Mensonides
of a variadic version for BOOST_PP_IS_EMPTY, and changed
in order to also support VC++. The code for the C++20
implementation of the macro, using the __VA_OPT__ preprocessor
construct, is the author's own and reuses code added to the
Boost preprocessor library by this author.

... = variadic input, for VC++8 this must be a single parameter

returns = 1 if the input is empty, 0 if it is not

It is recommended to append BOOST_PP_EMPTY() to whatever input
is being tested in order to avoid possible warning messages
from some compilers about no parameters being passed to the macro
when the input is truly empty.

*/

#if BOOST_VMD_MSVC_V8

#define BOOST_VMD_IS_EMPTY(sequence) \
BOOST_VMD_DETAIL_IS_EMPTY_IIF \
( \
BOOST_PP_IS_BEGIN_PARENS \
( \
sequence \
) \
) \
( \
BOOST_VMD_DETAIL_IS_EMPTY_GEN_ZERO, \
BOOST_VMD_DETAIL_IS_EMPTY_PROCESS \
) \
(sequence) \
/**/

#else

# if defined(__cplusplus) && __cplusplus > 201703L
#include <boost/preprocessor/facilities/is_empty.hpp>
#define BOOST_VMD_IS_EMPTY(...) \
BOOST_VMD_DETAIL_IS_EMPTY_IIF \
( \
) \
( \
BOOST_PP_IS_EMPTY_OPT, \
BOOST_VMD_IS_EMPTY_NO_OPT \
) \
(__VA_ARGS__) \
/**/
# else
#define BOOST_VMD_IS_EMPTY(...) \
BOOST_VMD_IS_EMPTY_NO_OPT(__VA_ARGS__) \
/**/
# endif
#define BOOST_VMD_IS_EMPTY_NO_OPT(...) \
BOOST_VMD_DETAIL_IS_EMPTY_IIF \
( \
BOOST_PP_IS_BEGIN_PARENS \
( \
__VA_ARGS__ \
) \
) \
( \
BOOST_VMD_DETAIL_IS_EMPTY_GEN_ZERO, \
BOOST_VMD_DETAIL_IS_EMPTY_PROCESS \
) \
(__VA_ARGS__) \
/**/
#endif /* BOOST_VMD_MSVC_V8 */