CODEWITHSUNDEEP
c++boostboost-fusion
arlogb
arlogb

Reputation: 681

How to identify types in boost fusion vector

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.

Upvotes: 4

Views: 1136

Answers (2)

mauve
mauve

Reputation: 2016

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

Upvotes: 6

arlogb
arlogb

Reputation: 681

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.

Upvotes: 0

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