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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 |