On 13-08-09 04:40 AM, Mathias Gaunard wrote:
On 07/08/13 22:25, Eric Niebler wrote:
On 13-08-07 12:58 PM, paul Fultz wrote:
As others have stated, `BOOST_PP_SEQ_FOR_EACH` is not reentrant. One simple workaround is to use deferred expressions, like this:
#define BOOST_PP_SEQ_FOR_EACH_R_ID() BOOST_PP_SEQ_FOR_EACH_R #define DEFER(x) x BOOST_PP_EMPTY()
#define S0 (0)(1)(2)(3) #define S1 (5)(6)(7)(8) #define M4(R, DATA, ELEM) (DATA,ELEM) #define M2(R, DATA, ELEM) DEFER(BOOST_PP_SEQ_FOR_EACH_R_ID)()(R, M4, ELEM, S1); BOOST_PP_EXPAND(BOOST_PP_SEQ_FOR_EACH_R(1, M2, ~, S0))
If more depths are needed, just add more `BOOST_PP_EXPAND` macros. Also, you can reuse the recursion state so you could write `M2` like this:
#define M2(R, DATA, ELEM) DEFER(BOOST_PP_SEQ_FOR_EACH_R_ID)()(1, M4, ELEM, S1);
or like this, if you don't know the original recursion state:
#define M2(R, DATA, ELEM) DEFER(BOOST_PP_SEQ_FOR_EACH_R_ID)()(BOOST_PP_DEC(R), M4, ELEM, S1);
I won't pretend to understand how this works, but it does. Thanks!
Why not just use BOOST_PP_REPEAT otherwise? It's simple and it always works.
Just replace ELEM by BOOST_PP_SEQ_ELEM(N, S0)
Isn't accessing the Nth element of a PP sequence O(N)? Seems to me that what Paul posted would be more efficient. -- Eric Niebler Boost.org