Re: [Boost-users] [fusion] making an inner struct boost fusion compatible?

Subject: Re: [Boost-users] [fusion] making an inner struct boost fusion compatible?
From: Oswin Krause (Oswin.Krause_at_[hidden])
Date: 2012-09-24 05:04:25

Hi,

so after a weekend of thinking about this issue, i am still not much 
nearer to an solution.

Everything begins with that i want to automatically adapt a structure 
to the needs of my library.

which is:
1. it is fusion compatible such that it's elements form a fusion 
seqeunce(easy)
2. there exist a container type storing the structure such, that for 
every element of structure a container exists (also easy).
3. These containers now shall also be a fusion sequence (aparently 
hard).

Th idea is, that one an algorithm can decide to only work on a small 
fraction of the heterogenous data having a nice memory layout at the 
same time.

This is my approach which failed:

//slightly simplified example
struct SomeStruct{
     int a;
     float b;
};
//specialisation for my interface. Will be a macro.
template<>
struct SequenceType<SomeStruct>{//sequence type of the structure i want 
to create

struct type: boost::fusion::sequence_facade<
        type,
        boost::fusion::random_access_traversal_tag
> {
                //create fusion sequence interface
                BOOST_FUSION_DEFINE_STRUCT_MEMBERS_IMPL(type, 
(std::vector<int>,a)(std::vector<float>b))

                //sequence interface
                typedef SomeStruct value_type;
                struct reference{...};//reference to an element
                struct const_reference{...};
                typedef ProxyIterator<type, value_type, reference > iterator;
                typedef ProxyIterator<const type, value_type, const_reference > 
const_iterator;
                iterator begin(){...}//naming collision :(
                const_iterator begin()const{...}//naming collision :(
                iterator end(){...}//naming collision :(
                const_iterator end()const{...}//naming collision :(
};
....
};

so what would be a good solution for my problem?

On 2012-09-21 09:52, Nathan Ridge wrote:
>> thanks for the reply.
>> Is it possible to just copy and rename the macro, or does it depend 
>> on
>> newer features of fusion? I need to be compatible with boost 1.45 so 
>> i
>> can't use it directly (also i need to add a few more functions to 
>> the
>> structure later on)
>
> BOOST_FUSION_DEFINE_STRUCT_INLINE is implemented using the 
> sequence_facade
> and iterator_facade extension mechanisms, which were present in Boost 
> 1.45
> [1] [2]. So, it should be straightforward to back-port the macro to 
> 1.45.
>
> Regards,
> Nate
>
> [1]
> 
> http://www.boost.org/doc/libs/1_45_0/libs/fusion/doc/html/fusion/extension/sequence_facade.html
> [2]
> 
> http://www.boost.org/doc/libs/1_45_0/libs/fusion/doc/html/fusion/extension/iterator_facade.html
>
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