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

   1 .. Sequences/Intrinsic Metafunctions//order
   2
   3 order
   4 =====
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     template<
  12           typename Sequence
  13         , typename Key
  14         >
  15     struct order
  16     {
  17         typedef |unspecified| type;
  18     };
  19
  20
  21
  22 Description
  23 -----------
  24
  25 Returns a unique unsigned |Integral Constant| associated with the key ``Key`` in
  26 ``Sequence``.
  27
  28
  29 Header
  30 ------
  31
  32 .. parsed-literal::
  33
  34     #include <boost/mpl/order.hpp>
  35
  36
  37 Model of
  38 --------
  39
  40 |Tag Dispatched Metafunction|
  41
  42
  43 Parameters
  44 ----------
  45
  46 +---------------+---------------------------+-----------------------------------------------+
  47 | Parameter     | Requirement               | Description                                   |
  48 +===============+===========================+===============================================+
  49 | ``Sequence``  | |Associative Sequence|    | A sequence to query.                          |
  50 +---------------+---------------------------+-----------------------------------------------+
  51 | ``Key``       | Any type                  | The queried key.                              |
  52 +---------------+---------------------------+-----------------------------------------------+
  53
  54
  55 Expression semantics
  56 --------------------
  57
  58 For any |Associative Sequence| ``s``, and arbitrary type ``key``:
  59
  60 .. parsed-literal::
  61
  62     typedef order<s,key>::type n;
  63
  64 :Return type:
  65     Unsigned |Integral Constant|.
  66
  67 :Semantics:
  68     If ``has_key<s,key>::value == true``, ``n`` is a unique unsigned
  69     |Integral Constant| associated with ``key`` in ``s``; otherwise,
  70     ``n`` is identical to ``void_``.
  71
  72
  73 Complexity
  74 ----------
  75
  76 Amortized constant time.
  77
  78
  79 Example
  80 -------
  81
  82 .. parsed-literal::
  83
  84     typedef map< pair<int,unsigned>, pair<char,long> > m;
  85
  86     BOOST_MPL_ASSERT_NOT(( is_same< order<m,int>::type, void\_ > ));
  87     BOOST_MPL_ASSERT(( is_same< order<m,long>::type,void\_ > ));
  88
  89
  90
  91 See also
  92 --------
  93
  94 |Associative Sequence|, |has_key|, |count|, |map|
  95
  96
  97 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
  98    Distributed under the Boost Software License, Version 1.0. (See accompanying
  99    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)