Hello Using the BOOST_PP_IS_EMPTY macro with string literal as parameter causes compiler warning: warning: pasting "BOOST_PP_IS_EMPTY_DEF_" and ""AA"" does not give a valid preprocessing token In order to avoid this warning I have reimplemented this macro as it is shown below. Could something similar be implemented by the preprocessor library. Cheers, Sergei #include <boost/preprocessor/if.hpp> #include <boost/preprocessor/tuple.hpp> #include <boost/preprocessor/facilities/is_empty.hpp> #define MY_BOOST_PP_IS_EMPTY(x) MY_BOOST_PP_IS_EMPTY_I(MY_BOOST_PP_IS_EMPTY_HELPER x) #define MY_BOOST_PP_IS_EMPTY_I(contents) MY_BOOST_PP_IS_EMPTY_II( contents() ) #define MY_BOOST_PP_IS_EMPTY_II(contents) MY_BOOST_PP_IS_EMPTY_III( contents ) #define MY_BOOST_PP_IS_EMPTY_III(contents) BOOST_PP_TUPLE_ELEM( 2, 0, ( MY_BOOST_PP_IS_EMPTY_DEF_ ## contents ) ) #define MY_BOOST_PP_IS_EMPTY_HELPER() MY_BOOST_PP_IS_EMPTY_TRUE #define MY_BOOST_PP_IS_EMPTY_DEF_MY_BOOST_PP_IS_EMPTY_TRUE 1 , #define MY_BOOST_PP_IS_EMPTY_DEF_MY_BOOST_PP_IS_EMPTY_HELPER 0 , #define TEST_CASE_1( x ) BOOST_PP_IF( BOOST_PP_IS_EMPTY( x ), is empty, x ) #define TEST_CASE_2( x ) BOOST_PP_IF( MY_BOOST_PP_IS_EMPTY( x ), is empty, x ) TEST_CASE_1( "" ) TEST_CASE_1( "AA" ) TEST_CASE_1( AA ) TEST_CASE_1( ) TEST_CASE_2( "" ) TEST_CASE_2( "AA" ) TEST_CASE_2( AA ) TEST_CASE_2( )