ceph/src/boost/libs/parameter/include/boost/parameter/aux_/unwrap_cv_reference.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 UNWRAP_CV_REFERENCE_050328_HPP
   7 #define UNWRAP_CV_REFERENCE_050328_HPP
   8
   9 #include <boost/parameter/aux_/yesno.hpp>
  10 #include <boost/mpl/bool.hpp>
  11 #include <boost/mpl/identity.hpp>
  12 #include <boost/mpl/eval_if.hpp>
  13
  14 namespace boost { template<class T> class reference_wrapper; }
  15
  16 namespace boost { namespace parameter { namespace aux {
  17
  18 //
  19 // reference_wrapper support -- because of the forwarding problem,
  20 // when passing arguments positionally by non-const reference, we
  21 // ask users of named parameter interfaces to use ref(x) to wrap
  22 // them.
  23 //
  24
  25 // is_cv_reference_wrapper returns mpl::true_ if T is of type
  26 // reference_wrapper<U> cv
  27 template <class U>
  28 yes_tag is_cv_reference_wrapper_check(reference_wrapper<U> const volatile*);
  29 no_tag is_cv_reference_wrapper_check(...);
  30
  31 template <class T>
  32 struct is_cv_reference_wrapper
  33 {
  34     BOOST_STATIC_CONSTANT(
  35         bool, value = (
  36             sizeof(is_cv_reference_wrapper_check((T*)0)) == sizeof(yes_tag)
  37         )
  38     );
  39
  40     typedef mpl::bool_<
  41 #if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
  42         is_cv_reference_wrapper::
  43 #endif
  44     value> type;
  45 };
  46
  47 // Needed for unwrap_cv_reference below. T might be const, so
  48 // eval_if might fail because of deriving from T const on EDG.
  49 template <class T>
  50 struct get_type
  51 {
  52     typedef typename T::type type;
  53 };
  54
  55 #if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
  56 template <class T, class is_reference_wrapper = typename is_cv_reference_wrapper<T>::type>
  57 struct unwrap_cv_reference
  58 {
  59     typedef T type;
  60 };
  61
  62 template <class T>
  63 struct unwrap_cv_reference<T const, mpl::false_>
  64 {
  65     typedef T const type;
  66 };
  67
  68 template <class T>
  69 struct unwrap_cv_reference<T, mpl::true_>
  70   : T
  71 {};
  72
  73 #else
  74 // Produces the unwrapped type to hold a reference to in named<>
  75 // Can't use boost::unwrap_reference<> here because it
  76 // doesn't handle the case where T = reference_wrapper<U> cv
  77 template <class T>
  78 struct unwrap_cv_reference
  79 {
  80     typedef typename mpl::eval_if<
  81         is_cv_reference_wrapper<T>
  82       , get_type<T>
  83       , mpl::identity<T>
  84     >::type type;
  85 };
  86 #endif
  87
  88 }}} // namespace boost::parameter::aux
  89
  90 #endif // UNWRAP_CV_REFERENCE_050328_HPP
  91