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

   1 .. Metafunctions/Logical Operations//or_ |20
   2
   3 or\_
   4 ====
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     template<
  12           typename F1
  13         , typename F2
  14         |...|
  15         , typename F\ *n* = |unspecified|
  16         >
  17     struct or\_
  18     {
  19         typedef |unspecified| type;
  20     };
  21
  22
  23
  24 Description
  25 -----------
  26
  27 Returns the result of short-circuit *logical or* (``||``) operation on its arguments.
  28
  29
  30 Header
  31 ------
  32
  33 .. parsed-literal::
  34
  35     #include <boost/mpl/or.hpp>
  36     #include <boost/mpl/logical.hpp>
  37
  38
  39 Parameters
  40 ----------
  41
  42 +---------------+---------------------------+-----------------------------------------------+
  43 | Parameter     | Requirement               | Description                                   |
  44 +===============+===========================+===============================================+
  45 | |F1...Fn|     | Nullary |Metafunction|    | Operation's arguments.                        |
  46 +---------------+---------------------------+-----------------------------------------------+
  47
  48
  49 Expression semantics
  50 --------------------
  51
  52 For arbitrary nullary |Metafunction|\ s |f1...fn|:
  53
  54 .. parsed-literal::
  55
  56     typedef or_<f1,f2,\ |...|\ ,f\ *n*\>::type r;
  57
  58 :Return type:
  59     |Integral Constant|.
  60
  61 :Semantics:
  62     ``r`` is ``true_`` if either of ``f1::type::value``, ``f2::type::value``,...
  63     ``fn::type::value`` expressions evaluates to ``true``, and ``false_`` otherwise;
  64     guarantees left-to-right evaluation; the operands subsequent to the first
  65     ``f``\ *i* metafunction that evaluates to ``true`` are not evaluated.
  66
  67 .. ..........................................................................
  68
  69 .. parsed-literal::
  70
  71     typedef or_<f1,f2,\ |...|\ ,f\ *n*\> r;
  72
  73 :Return type:
  74     |Integral Constant|.
  75
  76 :Semantics:
  77     Equivalent to
  78
  79     .. parsed-literal::
  80
  81         struct r : or_<f1,f2,\ |...|\ ,f\ *n*\>::type {};
  82
  83
  84 Example
  85 -------
  86
  87 .. parsed-literal::
  88
  89     struct unknown;
  90
  91     BOOST_MPL_ASSERT(( or_< true\_,true\_ > ));
  92     BOOST_MPL_ASSERT(( or_< false\_,true\_ > ));
  93     BOOST_MPL_ASSERT(( or_< true\_,false\_ > ));
  94     BOOST_MPL_ASSERT_NOT(( or_< false\_,false\_ > ));
  95     BOOST_MPL_ASSERT(( or_< true\_,unknown > )); // OK
  96     BOOST_MPL_ASSERT(( or_< true\_,unknown,unknown > )); // OK too
  97
  98
  99 See also
 100 --------
 101
 102 |Metafunctions|, |Logical Operations|, |and_|, |not_|
 103
 104
 105 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
 106    Distributed under the Boost Software License, Version 1.0. (See accompanying
 107    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)