Re: [Boost-users] Variant and Fusion

On Wed, Mar 10, 2010 at 01:46:30PM -0800, Steven Watanabe wrote:

Can you give an example of the kind of recursive variant and the sequence(s) that you want to get out of it?

Let this be the variant type typedef boost::make_recursive_variant< int, double, std::vectorboost::recursive_variant_ >::type variant; and this an instance of it std::vector<variant> vec; vec.push_back(42); vec.push_back(4.2); vec.push_back(vec); variant v = vec;

In particular how are the runtime values of the elements of the sequence to be determined?

Conceptually, I am thinking of a visitor that goes over the variant and flattens it. In the above example, the corresponding sequence would be [42, 4.2, 42, 4.2] which corresponds to a fusion::vector. Practically, I don't see a way how to get the type of the vector at runtime unless knowing in advance the type of the fusion vector (which could be a potential assumption). I was also talking about "chopping" the variant in disjunct sequences. By this, I mean that a visitor goes over the variant and creates several sequences, say [42] [4.2, 42] [42] for the above example. That's the scenario I ultimately target. Ideally, these sequences are only views (tiers) of the original variant.

Depending on what you're doing, you might be able to use the nested types typedef of variant, which is an MPL sequence.

Are you referring to the variant<T>::types MPL sequence? Matthias -- Matthias Vallentin vallentin@icsi.berkeley.edu http://www.icir.org/matthias