CODEWITHSUNDEEP
c++boost-variant
surfcode
surfcode

Reputation: 465

How to declare a boost recursive variant in mpl::list?

How can I make this recursive variant work? I'd like to have a container of variant, or container of container of variant.

template <class T>
class A 
{ 
    // ...
    T t_;
};

template <class T>
class AVariant
{
    typedef typename boost::make_variant_over<T>::type Type;
    Type t;

    // ...
};

template <class Container>
class Composite
{
    typedef typename Container::value_type T;
    Container container_of_any_;

    // ....
};

In main.cpp:

typedef AVariant<boost::mpl::list<
    A<int>,
    A<long>,
    boost::recursive_wrapper<Composite<std::vector<Any> > > // Compile error: 'Any' is not declared in this scope
> > Any;

I understand that Compoiste > is not right, but not sure how?

Edit: I've changed the following:

template <class T>
class AVariant
{
    typedef typename boost::make_recursive_variant_over<T>::type Type;
    Type t_;

    // ...

    template <class Archive>
    class SerializeVisitor : public boost::static_visitor<>
    {
        SerializeVisitor( Archive& ar ) : ar_(ar) {}
        template <typename U>
        void operator()( const U& t ) const
        {
            ar_ & BOOST_SERIALIZATION_NVP( t );
        }
    };

    friend class boost::serialization::access;
    template<class Archive>
    void serialize( Archive& ar, const unsigned int version )
    {
        boost::apply_visitor( SerializeVisitor<Archive>( ar ), t_ );
    }

};

Then instantiate using:

typedef AVariant<boost::mpl::list<
    A<double>,
    A<int>,
    std::vector<boost::recursive_variant_> // to make the recursion slightly simplier
> > Any;

And my AVariant has a visitor to serialize as above. It still gives compile error when serialization is invoked in main(). It seems to look for serialize() function for the class std::vector in the error:

const class std::vector<boost::variant<boost::detail::variant::recursive_flag<boost::detail::variant::over_sequence<boost::mpl::vector<A<double>, A<long int>, A, std::vector<boost::recursive_variant_, std::allocator<boost::recursive_variant_> >, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na> > >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>, std::allocator<boost::variant<boost::detail::variant::recursive_flag<boost::detail::variant::over_sequence<boost::mpl::vector<A<double>, A<long int>, A, std::vector<boost::recursive_variant_, std::allocator<boost::recursive_variant_> >, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na> > >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_> > >' has no member named 'serialize'

Upvotes: 0

Views: 600

Answers (1)

user1744056
user1744056

Reputation:

You need to use boost::make_recursive_variant instead of boost::recursive_wrapper with boost::recursive_variant_ in it.So you should try this:

typedef AVariant<boost::mpl::list<
A<int>,
A<long>,
boost::make_recursive_variant<Composite<std::vector<boost::recursive_variant_> > 
  >::type > > Any;

This can help you.

You should refer here: http://www.boost.org/doc/libs/1_54_0/doc/html/variant/tutorial.html#variant.tutorial.recursive.recursive-variant and here http://www.boost.org/doc/libs/1_54_0/boost/variant/recursive_variant.hpp for more information about recursive variants. If you want to serialize variant you should better use boost::variant visitation mechanism to write out the actual type contained in the variant:

 variant_serializer ser;
 boost::apply_visitor( ser, your_variant);

Upvotes: 1

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