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

   1 .. Macros/Introspection//BOOST_MPL_HAS_XXX_TRAIT_DEF
   2
   3 BOOST_MPL_HAS_XXX_TRAIT_DEF
   4 ===========================
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     #define BOOST_MPL_HAS_XXX_TRAIT_DEF(name) \\
  12         |unspecified-token-seq| \\
  13     /\*\*/
  14
  15
  16 Description
  17 -----------
  18
  19 Expands into a definition of a boolean unary |Metafunction| ``has_name``
  20 such that for any type ``x`` ``has_name<x>::value == true`` if and only
  21 if ``x`` is a class type and has a nested type memeber ``x::name``.
  22
  23 On the deficient compilers not capabale of performing the detection,
  24 ``has_name<x>::value`` always returns ``false``. A boolean configuraion
  25 macro, |BOOST_MPL_CFG_NO_HAS_XXX|, is provided to signal or override
  26 the "deficient" status of a particular compiler.
  27
  28 |Note:| |BOOST_MPL_HAS_XXX_TRAIT_DEF| is a simplified front end to
  29 the |BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF| introspection macro |-- end note|
  30
  31
  32 Header
  33 ------
  34
  35 .. parsed-literal::
  36
  37     #include <boost/mpl/has_xxx.hpp>
  38
  39
  40 Parameters
  41 ----------
  42
  43
  44 +---------------+-------------------------------+---------------------------------------------------+
  45 | Parameter     | Requirement                   | Description                                       |
  46 +===============+===============================+===================================================+
  47 | ``name``      | A legal identifier token      | A name of the member being detected.              |
  48 +---------------+-------------------------------+---------------------------------------------------+
  49
  50
  51 Expression semantics
  52 --------------------
  53
  54 For any legal C++ identifier ``name``:
  55
  56 .. parsed-literal::
  57
  58     BOOST_MPL_HAS_XXX_TRAIT_DEF(name)
  59
  60 :Precondition:
  61     Appears at namespace scope.
  62
  63 :Return type:
  64     None.
  65
  66 :Semantics:
  67     Equivalent to
  68
  69     .. parsed-literal::
  70
  71         BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF(
  72               BOOST_PP_CAT(has\_,name), name, false
  73             )
  74
  75
  76 Example
  77 -------
  78
  79 .. parsed-literal::
  80
  81     BOOST_MPL_HAS_XXX_TRAIT_DEF(xxx)
  82
  83     struct test1 {};
  84     struct test2 { void xxx(); };
  85     struct test3 { int xxx; };
  86     struct test4 { static int xxx(); };
  87     struct test5 { template< typename T > struct xxx {}; };
  88     struct test6 { typedef int xxx; };
  89     struct test7 { struct xxx; };
  90     struct test8 { typedef void (\*xxx)(); };
  91     struct test9 { typedef void (xxx)(); };
  92
  93     BOOST_MPL_ASSERT_NOT(( has_xxx<test1> ));
  94     BOOST_MPL_ASSERT_NOT(( has_xxx<test2> ));
  95     BOOST_MPL_ASSERT_NOT(( has_xxx<test3> ));
  96     BOOST_MPL_ASSERT_NOT(( has_xxx<test4> ));
  97     BOOST_MPL_ASSERT_NOT(( has_xxx<test5> ));
  98
  99     #if !defined(BOOST_MPL_CFG_NO_HAS_XXX)
 100     BOOST_MPL_ASSERT(( has_xxx<test6> ));
 101     BOOST_MPL_ASSERT(( has_xxx<test7> ));
 102     BOOST_MPL_ASSERT(( has_xxx<test8> ));
 103     BOOST_MPL_ASSERT(( has_xxx<test9> ));
 104     #endif
 105
 106     BOOST_MPL_ASSERT(( has_xxx<test6,true\_> ));
 107     BOOST_MPL_ASSERT(( has_xxx<test7,true\_> ));
 108     BOOST_MPL_ASSERT(( has_xxx<test8,true\_> ));
 109     BOOST_MPL_ASSERT(( has_xxx<test9,true\_> ));
 110
 111
 112 See also
 113 --------
 114
 115 |Macros|, |BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF|, |BOOST_MPL_CFG_NO_HAS_XXX|
 116
 117
 118 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
 119    Distributed under the Boost Software License, Version 1.0. (See accompanying
 120    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)