How to identify types in boost fusion vector

Question

How would one go about identifying the types inside a boost::fusion vector?

e.g.

fusion::vector<int, double, string> v;

then something that would let me identify v[0] as being type int, v[1] as type double and v[2] as type string.

Thanks.

There is no such thing as `v[0]` as I remember, because you need a compile-time construct. What did you try and what are you trying to do ? — Matthieu M., Oct 27 '12 at 14:32

score 6 · Accepted Answer · edited Mar 05 '14 at 19:18

6

In order to extract an element from a boost::fusion::vector you need to use boost::fusion::at_c, like this:

boost::fusion::vector<int, std::string> v(1, "hello");
std::cout << boost::fusion::at_c<0>(v) << std::endl; // prints 1

The type at position N is:

boost::fusion::result_of::at_c<boost::fusion::vector<int, std::string>, 1>::type

edited Mar 05 '14 at 19:18

answered Oct 27 '12 at 14:36

mauve

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arlogb · Answer 2 · 2012-10-27T14:41:55.097

0

This link describes what I was trying to do.

In detail, the following is what I was trying to achieve:

template<int N, typename T>
struct a_struct{
typedef typename T::value_type etype;
typedef typename boost::fusion::result_of::value_at<etype, boost::mpl::int_<N> >::type a_type;
};

Where T is a std::vector of boost::fusion vectors.

edited Oct 27 '12 at 14:41

answered Oct 27 '12 at 14:34

arlogb

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1
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How to identify types in boost fusion vector

2 Answers2