| .. Sequences/Intrinsic Metafunctions//at_c |
| |
| at_c |
| ==== |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| template< |
| typename Sequence |
| , long n |
| > |
| struct at_c |
| { |
| typedef |unspecified| type; |
| }; |
| |
| |
| |
| Description |
| ----------- |
| |
| Returns a type identical to the ``n``\ th element from the beginning of |
| the sequence. ``at_c<Sequence,n>::type`` is a shorcut notation for |
| ``at< Sequence, long_<n> >::type``. |
| |
| |
| Header |
| ------ |
| |
| .. parsed-literal:: |
| |
| #include <boost/mpl/at.hpp> |
| |
| |
| |
| Parameters |
| ---------- |
| |
| +---------------+-----------------------------------+-----------------------------------------------+ |
| | Parameter | Requirement | Description | |
| +===============+===================================+===============================================+ |
| | ``Sequence`` | |Forward Sequence| | A sequence to be examined. | |
| +---------------+-----------------------------------+-----------------------------------------------+ |
| | ``n`` | A compile-time integral constant | An offset from the beginning of the sequence | |
| | | | specifying the element to be retrieved. | |
| +---------------+-----------------------------------+-----------------------------------------------+ |
| |
| |
| Expression semantics |
| -------------------- |
| |
| |
| .. parsed-literal:: |
| |
| typedef at_c<Sequence,n>::type t; |
| |
| :Return type: |
| A type |
| |
| :Precondition: |
| ``0 <= n < size<Sequence>::value`` |
| |
| :Semantics: |
| Equivalent to |
| |
| .. parsed-literal:: |
| |
| typedef at< Sequence, long_<n> >::type t; |
| |
| |
| Complexity |
| ---------- |
| |
| +-------------------------------+-----------------------------------+ |
| | Sequence archetype | Complexity | |
| +===============================+===================================+ |
| | |Forward Sequence| | Linear. | |
| +-------------------------------+-----------------------------------+ |
| | |Random Access Sequence| | Amortized constant time. | |
| +-------------------------------+-----------------------------------+ |
| |
| |
| Example |
| ------- |
| |
| .. parsed-literal:: |
| |
| typedef range_c<long,10,50> range; |
| BOOST_MPL_ASSERT_RELATION( (at_c< range,0 >::type::value), ==, 10 ); |
| BOOST_MPL_ASSERT_RELATION( (at_c< range,10 >::type::value), ==, 20 ); |
| BOOST_MPL_ASSERT_RELATION( (at_c< range,40 >::type::value), ==, 50 ); |
| |
| |
| See also |
| -------- |
| |
| |Forward Sequence|, |Random Access Sequence|, |at|, |front|, |back| |
| |
| |
| .. copyright:: Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |