ceph/src/boost/libs/parameter/include/boost/parameter/keyword.hpp

   1 // Copyright Daniel Wallin, David Abrahams 2005. Use, modification and
   2 // distribution is subject to the Boost Software License, Version 1.0. (See
   3 // accompanying file LICENSE_1_0.txt or copy at
   4 // http://www.boost.org/LICENSE_1_0.txt)
   5
   6 #ifndef KEYWORD_050328_HPP
   7 #define KEYWORD_050328_HPP
   8
   9 #include <boost/parameter/aux_/unwrap_cv_reference.hpp>
  10 #include <boost/parameter/aux_/tag.hpp>
  11 #include <boost/parameter/aux_/default.hpp>
  12
  13 namespace boost { namespace parameter {
  14
  15 // Instances of unique specializations of keyword<...> serve to
  16 // associate arguments with parameter names.  For example:
  17 //
  18 //    struct rate_;           // parameter names
  19 //    struct skew_;
  20 //    namespace
  21 //    {
  22 //      keyword<rate_> rate;  // keywords
  23 //      keyword<skew_> skew;
  24 //    }
  25 //
  26 //    ...
  27 //
  28 //    f(rate = 1, skew = 2.4);
  29 //
  30 template <class Tag>
  31 struct keyword
  32 {
  33     template <class T>
  34     typename aux::tag<Tag, T>::type const
  35     operator=(T& x) const
  36     {
  37         typedef typename aux::tag<Tag, T>::type result;
  38         return result(x);
  39     }
  40
  41     template <class Default>
  42     aux::default_<Tag, Default>
  43     operator|(Default& default_) const
  44     {
  45         return aux::default_<Tag, Default>(default_);
  46     }
  47
  48     template <class Default>
  49     aux::lazy_default<Tag, Default>
  50     operator||(Default& default_) const
  51     {
  52         return aux::lazy_default<Tag, Default>(default_);
  53     }
  54
  55     template <class T>
  56     typename aux::tag<Tag, T const>::type const
  57     operator=(T const& x) const
  58     {
  59         typedef typename aux::tag<Tag, T const>::type result;
  60         return result(x);
  61     }
  62
  63     template <class Default>
  64     aux::default_<Tag, const Default>
  65     operator|(const Default& default_) const
  66     {
  67         return aux::default_<Tag, const Default>(default_);
  68     }
  69
  70     template <class Default>
  71     aux::lazy_default<Tag, Default>
  72     operator||(Default const& default_) const
  73     {
  74         return aux::lazy_default<Tag, Default>(default_);
  75     }
  76
  77  public: // Insurance against ODR violations
  78
  79     // People will need to define these keywords in header files.  To
  80     // prevent ODR violations, it's important that the keyword used in
  81     // every instantiation of a function template is the same object.
  82     // We provide a reference to a common instance of each keyword
  83     // object and prevent construction by users.
  84     static keyword<Tag> const instance;
  85
  86     // This interface is deprecated
  87     static keyword<Tag>& get()
  88     {
  89         return const_cast<keyword<Tag>&>(instance);
  90     }
  91 };
  92
  93 template <class Tag>
  94 keyword<Tag> const keyword<Tag>::instance = {};
  95
  96 // Reduces boilerplate required to declare and initialize keywords
  97 // without violating ODR.  Declares a keyword tag type with the given
  98 // name in namespace tag_namespace, and declares and initializes a
  99 // reference in an anonymous namespace to a singleton instance of that
 100 // type.
 101
 102 #define BOOST_PARAMETER_KEYWORD(tag_namespace,name)                 \
 103     namespace tag_namespace                                         \
 104     {                                                               \
 105       struct name                                                   \
 106       {                                                             \
 107           static char const* keyword_name()                         \
 108           {                                                         \
 109               return #name;                                         \
 110           }                                                         \
 111       };                                                            \
 112     }                                                               \
 113     namespace                                                       \
 114     {                                                               \
 115        ::boost::parameter::keyword<tag_namespace::name> const& name \
 116        = ::boost::parameter::keyword<tag_namespace::name>::instance;\
 117     }
 118
 119 }} // namespace boost::parameter
 120
 121 #endif // KEYWORD_050328_HPP
 122