Boost C++ Libraries

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at
Description

Returns the N-th element from the beginning of the sequence.

Synopsis
template <typename N, typename Sequence>
typename result_of::at<Sequence, N>::type
at(Sequence& seq);

template <typename N, typename Sequence>
typename result_of::at<Sequence const, N>::type
at(Sequence const& seq);
Parameters

Parameter

Requirement

Description

seq

Model of Random Access Sequence

The sequence we wish to investigate.

N

An MPL Integral Constant

An index from the beginning of the sequence.

Expression Semantics
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)))
Header
#include <boost/fusion/sequence/intrinsic/at.hpp>
#include <boost/fusion/include/at.hpp>
Example
vector<int, int, int> v(1, 2, 3);
assert(at<mpl::int_<1> >(v) == 2);

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