Re: [Boost-users] [preprocessor] BOOST_PP_IF with BOOST_PP_SEQ_ENUM as then-argument

Peter Bartlett schrieb:

Quoting Maximilian Matthe :

...

Hello!

#define seq (int)(int)

BOOST_PP_IF(1, BOOST_PP_SEQ_ENUM(seq), BOOST_PP_EMTPY)

does not expand to what i want: it should be int, int . G++ gives the following error:

test.cpp:20:1: macro "BOOST_PP_IIF" passed 4 arguments, but takes just 3 BOOST_PP_IIF

which is logical, because SEQ_ENUM expands to int, int and so if gets 4 arguments. I tried to surround SEQ_ENUM with IDENTITY but it's the same problem. Only surrounding SEQ_ENUM with () works, but then I have the () in the code, which I do not want. How can I solve this problem?

Max

You need to delay the evaluation of the SEQ_ENUM til after the IF:

#define DO_NOTHING(seq)

BOOST_PP_IF(1, BOOST_PP_SEQ_ENUM , DO_NOTHING)()

Ah thank you. This is quite tricky :-)