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Returns the M-th element from the beginning of the sequence.
template <typename M, typename Sequence> typenameresult_of::at<Sequence, N>::type at(Sequence& seq); template <typename M, typename Sequence> typenameresult_of::at<Sequence const, N>::type at(Sequence const& seq);
| Parameter | Requirement | Description | 
|---|---|---|
| 
                       | Model of Random Access Sequence | The sequence we wish to investigate. | 
| 
                       | An index from the beginning of the sequence. | 
at<M>(seq);
            Return type: Returns a reference to
            the M-th element from the beginning of the sequence seq
            if seq is mutable and
            e =
            o, where e
            is the M-th element from the beginning of the sequence, is a valid expression.
            Else, returns a type convertible to the M-th element from the beginning
            of the sequence.
          
            Precondition: 0
            <= M::value < 
            (where size(seq)seq is not Unbounded Sequence)
          
Semantics: Equivalent to
deref(advance<M>(begin(s)))
#include <boost/fusion/sequence/intrinsic/at.hpp> #include <boost/fusion/include/at.hpp>
vector<int, int, int> v(1, 2, 3);
assert(at<mpl::int_<1> >(v) == 2);