The BOOST_PP_DEDUCE_D macro manually deduces the state of the BOOST_PP_WHILE construct.

This macro is intended to avoid the use of automatic-recursion at deep expansion depths.  Automatic-recursion at such depths can be inefficient on some preprocessors.  It is not intended to be used directly with the invocation of macros with a _D suffix such as: If it is used in this context, the _D macro will fail.  The _D macros directly concatenate to the d parameter that is passed to them, which would prevent BOOST_PP_DEDUCE_D() from expanding.  Furthermore, it is pointless to use this macro in a situation such as this because it would already be too late to gain any efficiency.

Header:  <boost/preprocessor/control/deduce_d.hpp>

#include <boost/preprocessor/arithmetic/add.hpp>
#include <boost/preprocessor/arithmetic/inc.hpp>
#include <boost/preprocessor/arithmetic/sub.hpp>
#include <boost/preprocessor/control/deduce_d.hpp>
#include <boost/preprocessor/punctuation/comma_if.hpp>
#include <boost/preprocessor/repetition/repeat.hpp>
#include <boost/preprocessor/tuple/elem.hpp>

#define RANGE(first, last) \
   BOOST_PP_REPEAT( \
      BOOST_PP_INC( \
         BOOST_PP_SUB(last, first) \
      ), \
      RANGE_M, \
      (first, BOOST_PP_DEDUCE_D()) \
   ) \
   /**/

#define RANGE_M(z, n, data) \
   RANGE_M_2( \
      n, \
      BOOST_PP_TUPLE_ELEM(2, 0, data), \
      BOOST_PP_TUPLE_ELEM(2, 1, data) \
   ) \
   /**/

#define RANGE_M_2(n, first, d) \
   BOOST_PP_COMMA_IF(n) BOOST_PP_ADD_D(d, n, first) \
   /**/

RANGE(5, 10) // expands to 5, 6, 7, 8, 9, 10

© Copyright Housemarque Oy 2002
© Copyright Paul Mensonides 2002

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at www.boost.org/LICENSE_1_0.txt)