Re: [Boost-users] [fusion] Compile Error using BOOST_FUSION_DEFINE_STRUCT_INLINE with VC10 and GCC 4.2.1

Subject: Re: [Boost-users] [fusion] Compile Error using BOOST_FUSION_DEFINE_STRUCT_INLINE with VC10 and GCC 4.2.1
From: Nathan Ridge (zeratul976_at_[hidden])
Date: 2012-10-24 18:25:26

> > If anyone can suggest a workaround for these compiler bugs, I am
> > happy to
> > implement them.
> I have tried to understand what the macro generates and maybe we can
> fix it by using fusion/mpl instead of partial template specialization. I
> don't fully understand the macro, but maybe i am not too far off, so
> that my solution might still work.
>
> the need for partial template spcialization arised because basically
> the type/member list (A1, a1)(A2,a2)... is translated into
>
> typedef A1 t1_type;
> typedef A2 t2_type;
> ...
> t1_type& t1;//linked to a1
> t2_type& t2;//linked to a2
> ...
>
> or something very similar to it.
>
> thus you need to specialize deref to do something roughly like( i
> simplyfy here because i am too lazy to look up the original solution):
>
> template<int>
> struct deref{};
> template<>
> struct deref<1>{
> typedef t1_type& type;
> type call(Sequence& seq){
> return seq.t1;
> }
> };
> ...
>
> now think about the following:
> typedef boost::fusion::vector<A1&,A2&,...AN&> t_seq;
> t_seq t;//tied to a1...an
> template<int N>
> struct deref{
> typedef result_of::at_c<t_types,N> type;
> type call(Sequence& seq){
> return at_c<N>(seq.t);
> }
> };
>
> could this work? Of course this is detrimental to the compil times
> since fusion::vector needs to be itnroduced and instantiated. However
> this might just be the solution used for GCC<4.5 and MSVC, in this cas
> "slow" is better than "compiler gives up".

Nice idea! I think that would work.

Could you please file a Trac ticket for this with your example code?
I will post a patch there once I've implemented the workaround.

Regards,
Nate