at

template<
    typename Seq,
    typename M>
struct at
{
    typedef unspecified type;
};

Table 1.28. Parameters

Parameter	Requirement	Description
`Seq`	A model of Random Access Sequence	Argument sequence
`M`	An MPL Integral Constant	Index of element

result_of::at<Seq, M>::type

Return type: Any type.

Precondition: 0 <= M::value < result_of::size<Seq>::value (where Seq is not Unbounded Sequence)

Semantics: Returns the result type of using at to access the Mth element of Seq.

#include <boost/fusion/sequence/intrinsic/at.hpp>
#include <boost/fusion/include/at.hpp>

typedef vector<int,float,char> vec;
BOOST_MPL_ASSERT((boost::is_same<result_of::at<vec, boost::mpl::int_<1> >::type, float&>));

^[7] result_of::at reflects the actual return type of the function at. Sequence(s) typically return references to its elements via the at function. If you want to get the actual element type, use result_of::value_at

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