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

24 Sep 2012

      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 iterator;
		typedef ProxyIterator 
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/s...
[2]
http://www.boost.org/doc/libs/1_45_0/libs/fusion/doc/html/fusion/extension/i...
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Re: [Boost-users] [fusion] making an inner struct boost fusion compatible?

Oswin Krause