source: NonGTP/Boost/boost/parameter/aux_/unwrap_cv_reference.hpp @ 857

Revision 857, 2.5 KB checked in by igarcia, 19 years ago (diff)
Line 
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
14namespace boost { template<class T> class reference_wrapper; }
15
16namespace 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
27template <class U>
28yes_tag is_cv_reference_wrapper_check(reference_wrapper<U> const volatile*);
29no_tag is_cv_reference_wrapper_check(...);
30
31template <class T>
32struct 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#if BOOST_WORKAROUND(MSVC, == 1200)
48template <>
49struct is_cv_reference_wrapper<int>
50  : mpl::false_ {};
51#endif
52
53// Needed for unwrap_cv_reference below. T might be const, so
54// eval_if might fail because of deriving from T const on EDG.
55template <class T>
56struct get_type
57{
58    typedef typename T::type type;
59};
60
61#if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
62template <class T, class is_reference_wrapper = typename is_cv_reference_wrapper<T>::type>
63struct unwrap_cv_reference
64{
65    typedef T type;
66};
67
68template <class T>
69struct unwrap_cv_reference<T const, mpl::false_>
70{
71    typedef T const type;
72};
73
74template <class T>
75struct unwrap_cv_reference<T, mpl::true_>
76  : T
77{};
78
79#else
80// Produces the unwrapped type to hold a reference to in named<>
81// Can't use boost::unwrap_reference<> here because it
82// doesn't handle the case where T = reference_wrapper<U> cv
83template <class T>
84struct unwrap_cv_reference
85{
86    typedef typename mpl::eval_if<
87        is_cv_reference_wrapper<T>
88      , get_type<T>
89      , mpl::identity<T>
90    >::type type;
91};
92#endif
93
94}}} // namespace boost::parameter::aux
95
96#endif // UNWRAP_CV_REFERENCE_050328_HPP
97
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