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

   1 .. Sequences/Intrinsic Metafunctions//has_key
   2
   3 has_key
   4 =======
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     template<
  12           typename Sequence
  13         , typename Key
  14         >
  15     struct has_key
  16     {
  17         typedef |unspecified| type;
  18     };
  19
  20
  21
  22 Description
  23 -----------
  24
  25 Returns a true-valued |Integral Constant| if ``Sequence`` contains an element
  26 with key ``Key``.
  27
  28
  29 Header
  30 ------
  31
  32 .. parsed-literal::
  33
  34     #include <boost/mpl/has_key.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 has_key<s,key>::type c;
  63
  64 :Return type:
  65     Boolean |Integral Constant|.
  66
  67 :Semantics:
  68     ``c::value == true`` if ``key`` is in ``s``'s set of keys; otherwise
  69     ``c::value == false``.
  70
  71
  72 Complexity
  73 ----------
  74
  75 Amortized constant time.
  76
  77
  78 Example
  79 -------
  80
  81 .. parsed-literal::
  82
  83     typedef map< pair<int,unsigned>, pair<char,long> > m;
  84     BOOST_MPL_ASSERT_NOT(( has_key<m,long> ));
  85
  86     typedef insert< m, pair<long,unsigned long> > m1;
  87     BOOST_MPL_ASSERT(( has_key<m1,long> ));
  88
  89
  90 See also
  91 --------
  92
  93 |Associative Sequence|, |count|, |insert|, |erase_key|
  94
  95
  96 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
  97    Distributed under the Boost Software License, Version 1.0. (See accompanying
  98    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)