Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
![[Home]](../mpl_logo.jpg){kind=logo}
at
template<
typename Sequence
, typename N
>
struct at
{
typedef unspecified type;
};
Returns a type identical to the N-th element from the beginning of the sequence.
#include "boost/mpl/at.hpp"
| Parameter | Requirement | Description |
|---|---|---|
Sequence | A model of Forward Sequence | A sequence to be examined. |
N | A model of Integral Constant | The offset from the beginning of the sequence that specifies the element to be retrieved. |
| Expression | Expression type | Precondition | Semantics | Postcondition |
|---|---|---|---|---|
typedef at<Sequence,N>::type t; | A type | 0 <= N::value < size<Sequence>::type::value | Equivalent to typedef advance< begin<Sequence>::type,N >::type::type t; |
Depends on the implementation of the particular sequence it is applied to. Linear in the worst case, or amortized constant time.
typedef range_c<long,10,50> range; BOOST_STATIC_ASSERT(at< range, int_<0> >::type::value == 10); BOOST_STATIC_ASSERT(at< range, int_<10> >::type::value == 20); BOOST_STATIC_ASSERT(at< range, int_<40> >::type::value == 50);
Forward Sequence, at_c, front, back