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Returns the N-th element from the beginning of the sequence.
template <typename N, typename Sequence> typenameresult_of::at<Sequence, N>::type at(Sequence& seq); template <typename N, typename Sequence> typenameresult_of::at<Sequence const, N>::type at(Sequence const& seq);
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Parameter |
Requirement |
Description |
|---|---|---|
|
|
Model of Random Access Sequence |
The sequence we wish to investigate. |
|
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An index from the beginning of the sequence. |
at<N>(seq);
Return type: Returns a reference to
the N-th element from the beginning of the sequence seq
if seq is mutable and
e =
o, where e
is the N-th element from the beginning of the sequence, is a valid expression.
Else, returns a type convertable to the N-th element from the beginning
of the sequence.
Precondition: 0
<= N::value <
size(s)
Semantics: Equivalent to
deref(advance<N>(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);