ceph/src/boost/libs/mpl/doc/src/refmanual/at_c.rst

   1 .. Sequences/Intrinsic Metafunctions//at_c
   2
   3 at_c
   4 ====
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     template<
  12           typename Sequence
  13         , long n
  14         >
  15     struct at_c
  16     {
  17         typedef |unspecified| type;
  18     };
  19
  20
  21
  22 Description
  23 -----------
  24
  25 Returns a type identical to the ``n``\ th element from the beginning of
  26 the sequence. ``at_c<Sequence,n>::type`` is a shorcut notation for
  27 ``at< Sequence, long_<n> >::type``.
  28
  29
  30 Header
  31 ------
  32
  33 .. parsed-literal::
  34
  35     #include <boost/mpl/at.hpp>
  36
  37
  38
  39 Parameters
  40 ----------
  41
  42 +---------------+-----------------------------------+-----------------------------------------------+
  43 | Parameter     | Requirement                       | Description                                   |
  44 +===============+===================================+===============================================+
  45 | ``Sequence``  | |Forward Sequence|                | A sequence to be examined.                    |
  46 +---------------+-----------------------------------+-----------------------------------------------+
  47 | ``n``         | A compile-time integral constant  | An offset from the beginning of the sequence  |
  48 |               |                                   | specifying the element to be retrieved.       |
  49 +---------------+-----------------------------------+-----------------------------------------------+
  50
  51
  52 Expression semantics
  53 --------------------
  54
  55
  56 .. parsed-literal::
  57
  58     typedef at_c<Sequence,n>::type t;
  59
  60 :Return type:
  61     A type
  62
  63 :Precondition:
  64     ``0 <= n < size<Sequence>::value``
  65
  66 :Semantics:
  67     Equivalent to
  68
  69     .. parsed-literal::
  70
  71        typedef at< Sequence, long_<n> >::type t;
  72
  73
  74 Complexity
  75 ----------
  76
  77 +-------------------------------+-----------------------------------+
  78 | Sequence archetype            | Complexity                        |
  79 +===============================+===================================+
  80 | |Forward Sequence|            | Linear.                           |
  81 +-------------------------------+-----------------------------------+
  82 | |Random Access Sequence|      | Amortized constant time.          |
  83 +-------------------------------+-----------------------------------+
  84
  85
  86 Example
  87 -------
  88
  89 .. parsed-literal::
  90
  91     typedef range_c<long,10,50> range;
  92     BOOST_MPL_ASSERT_RELATION( (at_c< range,0 >::type::value), ==, 10 );
  93     BOOST_MPL_ASSERT_RELATION( (at_c< range,10 >::type::value), ==, 20 );
  94     BOOST_MPL_ASSERT_RELATION( (at_c< range,40 >::type::value), ==, 50 );
  95
  96
  97 See also
  98 --------
  99
 100 |Forward Sequence|, |Random Access Sequence|, |at|, |front|, |back|
 101
 102
 103 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
 104    Distributed under the Boost Software License, Version 1.0. (See accompanying
 105    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)