Re: [Boost-users] [fusion] probably a bug in result_of::join

Subject: Re: [Boost-users] [fusion] probably a bug in result_of::join
From: Christopher Schmidt (mr.chr.schmidt_at_[hidden])
Date: 2009-10-14 09:27:04

Yeah, this is a major issue of the current fusion implementation. The 
result_of::-metafunctions do not regard that the actual functions take 
const-qualified arguments only. On top of that the documentation is 
outdated and misleading.

In your particular case

result_of::join< vector<> const, vector<> const>::type j = join(v1, v2);

should work fine.

My C++0x port of fusion introduces non-const arguments for the algorithm 
functions and a new result_of::-concept which allows passing 
(optionally) cv and ref qualified types.

-Christopher

jl schrieb:
> This is nearly a copy-paste from the doc (and agrees with intuition):
> #include <boost/fusion/algorithm/transformation/join.hpp>
> #include <boost/fusion/include/vector.hpp>
> #include <boost/fusion/include/join.hpp>
> void foo() {
>  using namespace boost::fusion;
>  vector<> v1, v2;
>  result_of::join< vector<>, vector<> >::type j = join(v1, v2);
> }
> ...but it doesn't compile (msvc9, boost 1.40):
> c:\UserTemp\x54209\BoostTests\Any\main.cpp(20) : error C2440: 
> 'initializing' : cannot convert from 
> 'boost::fusion::result_of::join<LhSequence,RhSequence>::type' to 
> 'boost::fusion::joint_view<Sequence1,Sequence2>'
>        with
>        [
>            LhSequence=const boost::fusion::vector<>,
>            RhSequence=const boost::fusion::vector<>
>        ]
>        and
>        [
>            Sequence1=boost::fusion::vector<>,
>            Sequence2=boost::fusion::vector<>
>        ]
>        No constructor could take the source type, or constructor 
> overload resolution was ambiguous
> J-L