Re: [Boost-users] Variant and Fusion

AMDG Matthias Vallentin wrote:

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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).

You have to know the type of the vector at compile time.

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]

I think the easiest way is probably to create a runtime iterator that walks over the vector and recurses into any variants that it contains. Then you can use fusion's algorithms to iterate over the fusion::vector and the vector in parallel.

for the above example. That's the scenario I ultimately target. Ideally, these sequences are only views (tiers) of the original variant.

If you want it to be a view, you can use a fusion vector of references.

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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?

Yes. In Christ, Steven Watanabe