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

   1 .. Macros/Introspection//BOOST_MPL_HAS_XXX_TEMPLATE_DEF
   2
   3 .. Copyright Daniel Walker 2007.
   4 .. Distributed under the Boost
   5 .. Software License, Version 1.0. (See accompanying
   6 .. file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   7
   8 BOOST_MPL_HAS_XXX_TEMPLATE_DEF
   9 ==============================
  10
  11 Synopsis
  12 --------
  13
  14 .. parsed-literal::
  15
  16     #define BOOST_MPL_HAS_XXX_TEMPLATE_DEF(name) \\
  17         |unspecified-token-seq| \\
  18     /\*\*/
  19
  20
  21 Description
  22 -----------
  23
  24 Expands into the definition of a boolean |Metafunction| ``has_name``
  25 such that for any type ``x`` ``has_name<x>::value == true`` if and
  26 only if ``x`` is a class type and has a nested template member
  27 ``x::template name`` with no more than
  28 |BOOST_MPL_LIMIT_METAFUNCTION_ARITY| parameters.
  29
  30 On deficient compilers not capable of performing the detection,
  31 ``has_name<x>::value`` is always ``false``. A boolean configuration
  32 macro, |BOOST_MPL_CFG_NO_HAS_XXX_TEMPLATE|, is provided to signal or
  33 override the "deficient" status of a particular compiler.
  34
  35 |Note:| |BOOST_MPL_HAS_XXX_TEMPLATE_DEF| is a simplified front end to
  36 the |BOOST_MPL_HAS_XXX_TEMPLATE_NAMED_DEF| introspection macro |-- end
  37 note|
  38
  39
  40 Header
  41 ------
  42
  43 .. parsed-literal::
  44
  45     #include <boost/mpl/has_xxx.hpp>
  46
  47
  48 Parameters
  49 ----------
  50
  51
  52 +---------------+-------------------------------+---------------------------------------------------+
  53 | Parameter     | Requirement                   | Description                                       |
  54 +===============+===============================+===================================================+
  55 | ``name``      | A legal identifier token      | A name of the template member being detected.     |
  56 +---------------+-------------------------------+---------------------------------------------------+
  57
  58
  59 Expression semantics
  60 --------------------
  61
  62 For any legal C++ identifier ``name``:
  63
  64 .. parsed-literal::
  65
  66     BOOST_MPL_HAS_XXX_TEMPLATE_DEF(name)
  67
  68 :Precondition:
  69     Appears at namespace scope.
  70
  71 :Return type:
  72     None.
  73
  74 :Semantics:
  75     Equivalent to
  76
  77     .. parsed-literal::
  78
  79         BOOST_MPL_HAS_XXX_TEMPLATE_NAMED_DEF(
  80               BOOST_PP_CAT(has\_,name), name, false
  81             )
  82
  83
  84 Example
  85 -------
  86
  87 .. parsed-literal::
  88
  89     BOOST_MPL_HAS_XXX_TEMPLATE_DEF(xxx)
  90
  91     struct test1  {};
  92     struct test2  { void xxx(); };
  93     struct test3  { int xxx; };
  94     struct test4  { static int xxx(); };
  95     struct test5  { typedef int xxx; };
  96     struct test6  { struct xxx; };
  97     struct test7  { typedef void (\*xxx)(); };
  98     struct test8  { typedef void (xxx)(); };
  99     struct test9  { template< class T > struct xxx {}; };
 100
 101     BOOST_MPL_ASSERT_NOT(( has_xxx<test1> ));
 102     BOOST_MPL_ASSERT_NOT(( has_xxx<test2> ));
 103     BOOST_MPL_ASSERT_NOT(( has_xxx<test3> ));
 104     BOOST_MPL_ASSERT_NOT(( has_xxx<test4> ));
 105     BOOST_MPL_ASSERT_NOT(( has_xxx<test5> ));
 106     BOOST_MPL_ASSERT_NOT(( has_xxx<test6> ));
 107     BOOST_MPL_ASSERT_NOT(( has_xxx<test7> ));
 108     BOOST_MPL_ASSERT_NOT(( has_xxx<test8> ));
 109
 110     #if !defined(BOOST_MPL_CFG_NO_HAS_XXX_TEMPLATE)
 111     BOOST_MPL_ASSERT(( has_xxx<test9> ));
 112     #endif
 113
 114     BOOST_MPL_ASSERT(( has_xxx<test9, true\_> ));
 115
 116
 117 See also
 118 --------
 119
 120 |Macros|, |BOOST_MPL_HAS_XXX_TEMPLATE_NAMED_DEF|,
 121 |BOOST_MPL_CFG_NO_HAS_XXX_TEMPLATE|, |BOOST_MPL_LIMIT_METAFUNCTION_ARITY|
 122