Re: [Boost-bugs] [Boost C++ Libraries] #7769: BOOST_MPL_LIMIT_METAFUNCTION_ARITY > 8 causes compilation error on gcc

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #7769: BOOST_MPL_LIMIT_METAFUNCTION_ARITY > 8 causes compilation error on gcc
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-02-08 14:33:17

#7769: BOOST_MPL_LIMIT_METAFUNCTION_ARITY > 8 causes compilation error on gcc
------------------------------------+---------------------------------
  Reporter:  Adam Lach <salvage@…>  |      Owner:  agurtovoy
      Type:  Bugs                   |     Status:  new
 Milestone:  To Be Determined       |  Component:  mpl
   Version:  Boost 1.52.0           |   Severity:  Problem
Resolution:                         |   Keywords:  arity, metafunction
------------------------------------+---------------------------------

Comment (by brunocodutra@…):

 I found the issue to be the definition of BOOST_MPL_PP_RANGE in
 aux_/preprocessor/range.hpp:

 {{{
 #define BOOST_MPL_PP_RANGE(first, length) \
     BOOST_PP_SEQ_SUBSEQ((0)(1)(2)(3)(4)(5)(6)(7)(8)(9), first, length) \
 /**/
 }}}

 It is hardcoded to generate a range of at most 8 elements, hence the
 observed issue when trying to increase BOOST_MPL_LIMIT_METAFUNCTION_ARITY
 past 8.

 A fairly straightforward workaround is to redefine BOOST_MPL_PP_RANGE so
 as to generate a sequence of adequate length using boost preprocessor:


 {{{
 #include <boost/mpl/aux_/preprocessor/range.hpp>
 #include <boost/preprocessor/enum.hpp>
 #include <boost/preprocessor/tuple.hpp>
 #include <boost/preprocessor/arithmetic.hpp>
 #include <boost/preprocessor/punctuation.hpp>

 #define COUNT(z, n, _) n

 #undef BOOST_MPL_PP_RANGE
 #define BOOST_MPL_PP_RANGE(first, length) \
     BOOST_PP_SEQ_SUBSEQ( \
         BOOST_PP_TUPLE_TO_SEQ( \
                 BOOST_PP_ADD(first, length), \
                 BOOST_PP_LPAREN() \
                 BOOST_PP_ENUM(BOOST_PP_ADD(first, length), COUNT, _) \
                 BOOST_PP_RPAREN() \
         ), \
         first, length \
     ) \
 /**/
 }}}


 This compiled just fine on my setup.

 {{{
 3.18.5-1-ARCH #1 SMP PREEMPT Fri Jan 30 07:31:50 CET 2015
 clang version 3.5.1 (tags/RELEASE_351/final)
 Target: x86_64-unknown-linux-gnu
 Thread model: posix
 }}}

 I'd be most pleased to set up a patch for this in case it is required.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7769#comment:1>
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