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Boost.Fusion Sequence Wrap

I’m looking for a way to create a wrapper for a Boost.Fusion sequence, which itself is a Fusion sequence and forwards all the “calls” to its wrapped sequence. Something in the lines

template< typename Sequence >
struct sequence_wrapper
{
    explicit sequence_wrapper( Sequence const& s ) : seq( s ){}

    Sequence seq;
};

where is sequence_wrapper< Sequence >also a Fusion sequence, and works just like Sequence. The reason I need this is because I have several functions that work with Fusion sequences (where all elements satisfy some special requirements), and I would like to add some syntactic sugar, for which I need a special type to add overloaded operators. I don't need the result of operations on sequence_wrapper to return sequence_wrapper, but only syntax-related sugar-related calls return a (manually) wrapped sequence. For example, adding elements to a sequence using the comma operator (multiple Boost.Assign sequences for Fusion):

template< typename Sequence, typename T >
sequence_wrapper<
    typename boost::fusion::result_of::push_back<
        Sequence const&
      , T
    >::type
> operator ,( Sequence const& seq, T const& v )
{
    return
        sequence_wrapper<
            typename boost::fusion::result_of::push_back<
                Sequence const&
              , T
            >::type
        >( boost::fusion::push_back( seq, v ) )
        ;
}

( )? Fusion , , Fusion. + tag_of , ? , ?

+5
1

:

template<
    typename Derived
  , typename Sequence
  , typename TraversalTag = 
        typename boost::fusion::traits::category_of< Sequence >::type
  , typename IsView =
        typename boost::fusion::traits::is_view< Sequence >::type
>
class fusion_sequence_wrapper
  : public boost::fusion::sequence_facade< Derived, TraversalTag, IsView >
{
    typedef Sequence base_sequence_type;

public:
    explicit fusion_sequence_wrapper( base_sequence_type const& sequence )
      : _seq( sequence )
    {}

    base_sequence_type const& base() const
    {
        return _seq;
    }
    base_sequence_type& base()
    {
        return _seq;
    }

public:
    template< typename Seq >
    struct begin
    {
        typedef
            typename boost::fusion::result_of::begin<
                typename boost::mpl::if_<
                    boost::is_const< Seq >
                  , base_sequence_type const
                  , base_sequence_type
                >::type
            >::type type;

        static type call( Seq& s ){ return boost::fusion::begin( s._seq ); }
    };

    template< typename Seq >
    struct end
    {
        typedef
            typename boost::fusion::result_of::end<
                typename boost::mpl::if_<
                    boost::is_const< Seq >
                  , base_sequence_type const
                  , base_sequence_type
                >::type
            >::type type;

        static type call( Seq& s ){ return boost::fusion::end( s._seq ); }
    };

    template< typename Seq >
    struct size
    {
        typedef
            typename boost::fusion::result_of::size<
                typename boost::mpl::if_<
                    boost::is_const< Seq >
                  , base_sequence_type const
                  , base_sequence_type
                >::type
            >::type type;

        static type call( Seq& s ){ return boost::fusion::size( s._seq ); }
    };

    template< typename Seq >
    struct empty
    {
        typedef
            typename boost::fusion::result_of::empty<
                typename boost::mpl::if_<
                    boost::is_const< Seq >
                  , base_sequence_type const
                  , base_sequence_type
                >::type
            >::type type;

        static type call( Seq& s ){ return boost::fusion::empty( s._seq ); }
    };

    template< typename Seq, typename N >
    struct at
    {
        typedef
            typename boost::fusion::result_of::at<
                typename boost::mpl::if_<
                    boost::is_const< Seq >
                  , base_sequence_type const
                  , base_sequence_type
                >::type
              , N
            >::type type;

        static type call( Seq& s ){ return boost::fusion::at( s._seq ); }
    };

    template< typename Seq, typename N >
    struct value_at
    {
        typedef
            typename boost::fusion::result_of::value_at<
                typename boost::mpl::if_<
                    boost::is_const< Seq >
                  , base_sequence_type const
                  , base_sequence_type
                >::type
              , N
            >::type type;
    };

private:
    base_sequence_type _seq;
};
+4

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