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1 | // (C) Copyright 2009-2011 Frederic Bron, Robert Stewart, Steven Watanabe & Roman Perepelitsa. |
2 | // | |
3 | // Use, modification and distribution are subject to the Boost Software License, | |
4 | // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at | |
5 | // http://www.boost.org/LICENSE_1_0.txt). | |
6 | // | |
7 | // See http://www.boost.org/libs/type_traits for most recent version including documentation. | |
8 | ||
9 | #include <boost/config.hpp> | |
10 | #include <boost/type_traits/detail/yes_no_type.hpp> | |
11 | #include <boost/type_traits/integral_constant.hpp> | |
12 | #include <boost/type_traits/is_const.hpp> | |
13 | #include <boost/type_traits/is_fundamental.hpp> | |
14 | #include <boost/type_traits/is_integral.hpp> | |
15 | #include <boost/type_traits/is_pointer.hpp> | |
16 | #include <boost/type_traits/is_same.hpp> | |
17 | #include <boost/type_traits/is_void.hpp> | |
18 | #include <boost/type_traits/remove_cv.hpp> | |
19 | #include <boost/type_traits/remove_pointer.hpp> | |
20 | #include <boost/type_traits/remove_reference.hpp> | |
21 | ||
22 | // cannot include this header without getting warnings of the kind: | |
23 | // gcc: | |
24 | // warning: value computed is not used | |
25 | // warning: comparison between signed and unsigned integer expressions | |
26 | // msvc: | |
27 | // warning C4146: unary minus operator applied to unsigned type, result still unsigned | |
28 | // warning C4804: '-' : unsafe use of type 'bool' in operation | |
29 | // cannot find another implementation -> declared as system header to suppress these warnings. | |
30 | #if defined(__GNUC__) | |
31 | # pragma GCC system_header | |
32 | #elif defined(BOOST_MSVC) | |
33 | # pragma warning ( push ) | |
34 | # pragma warning ( disable : 4146 4804 4913 4244) | |
35 | # if BOOST_WORKAROUND(BOOST_MSVC_FULL_VER, >= 140050000) | |
36 | # pragma warning ( disable : 6334) | |
37 | # endif | |
38 | #endif | |
39 | ||
40 | ||
41 | ||
42 | namespace boost { | |
43 | namespace detail { | |
44 | ||
45 | // This namespace ensures that argument-dependent name lookup does not mess things up. | |
46 | namespace BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl) { | |
47 | ||
48 | // 1. a function to have an instance of type T without requiring T to be default | |
49 | // constructible | |
50 | template <typename T> T &make(); | |
51 | ||
52 | ||
53 | // 2. we provide our operator definition for types that do not have one already | |
54 | ||
55 | // a type returned from operator BOOST_TT_TRAIT_OP when no such operator is | |
56 | // found in the type's own namespace (our own operator is used) so that we have | |
57 | // a means to know that our operator was used | |
58 | struct no_operator { }; | |
59 | ||
60 | // this class allows implicit conversions and makes the following operator | |
61 | // definition less-preferred than any other such operators that might be found | |
62 | // via argument-dependent name lookup | |
63 | struct any { template <class T> any(T const&); }; | |
64 | ||
65 | // when operator BOOST_TT_TRAIT_OP is not available, this one is used | |
66 | no_operator operator BOOST_TT_TRAIT_OP (const any&); | |
67 | ||
68 | ||
69 | // 3. checks if the operator returns void or not | |
70 | // conditions: Rhs!=void | |
71 | ||
72 | // we first redefine "operator," so that we have no compilation error if | |
73 | // operator BOOST_TT_TRAIT_OP returns void and we can use the return type of | |
74 | // (BOOST_TT_TRAIT_OP rhs, returns_void_t()) to deduce if | |
75 | // operator BOOST_TT_TRAIT_OP returns void or not: | |
76 | // - operator BOOST_TT_TRAIT_OP returns void -> (BOOST_TT_TRAIT_OP rhs, returns_void_t()) returns returns_void_t | |
77 | // - operator BOOST_TT_TRAIT_OP returns !=void -> (BOOST_TT_TRAIT_OP rhs, returns_void_t()) returns int | |
78 | struct returns_void_t { }; | |
79 | template <typename T> int operator,(const T&, returns_void_t); | |
80 | template <typename T> int operator,(const volatile T&, returns_void_t); | |
81 | ||
82 | // this intermediate trait has member value of type bool: | |
83 | // - value==true -> operator BOOST_TT_TRAIT_OP returns void | |
84 | // - value==false -> operator BOOST_TT_TRAIT_OP does not return void | |
85 | template < typename Rhs > | |
86 | struct operator_returns_void { | |
87 | // overloads of function returns_void make the difference | |
88 | // yes_type and no_type have different size by construction | |
89 | static ::boost::type_traits::yes_type returns_void(returns_void_t); | |
90 | static ::boost::type_traits::no_type returns_void(int); | |
91 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(::boost::type_traits::yes_type)==sizeof(returns_void((BOOST_TT_TRAIT_OP make<Rhs>(),returns_void_t()))))); | |
92 | }; | |
93 | ||
94 | ||
95 | // 4. checks if the return type is Ret or Ret==dont_care | |
96 | // conditions: Rhs!=void | |
97 | ||
98 | struct dont_care { }; | |
99 | ||
100 | template < typename Rhs, typename Ret, bool Returns_void > | |
101 | struct operator_returns_Ret; | |
102 | ||
103 | template < typename Rhs > | |
104 | struct operator_returns_Ret < Rhs, dont_care, true > { | |
105 | BOOST_STATIC_CONSTANT(bool, value = true); | |
106 | }; | |
107 | ||
108 | template < typename Rhs > | |
109 | struct operator_returns_Ret < Rhs, dont_care, false > { | |
110 | BOOST_STATIC_CONSTANT(bool, value = true); | |
111 | }; | |
112 | ||
113 | template < typename Rhs > | |
114 | struct operator_returns_Ret < Rhs, void, true > { | |
115 | BOOST_STATIC_CONSTANT(bool, value = true); | |
116 | }; | |
117 | ||
118 | template < typename Rhs > | |
119 | struct operator_returns_Ret < Rhs, void, false > { | |
120 | BOOST_STATIC_CONSTANT(bool, value = false); | |
121 | }; | |
122 | ||
123 | template < typename Rhs, typename Ret > | |
124 | struct operator_returns_Ret < Rhs, Ret, true > { | |
125 | BOOST_STATIC_CONSTANT(bool, value = false); | |
126 | }; | |
127 | ||
128 | // otherwise checks if it is convertible to Ret using the sizeof trick | |
129 | // based on overload resolution | |
130 | // condition: Ret!=void and Ret!=dont_care and the operator does not return void | |
131 | template < typename Rhs, typename Ret > | |
132 | struct operator_returns_Ret < Rhs, Ret, false > { | |
133 | static ::boost::type_traits::yes_type is_convertible_to_Ret(Ret); // this version is preferred for types convertible to Ret | |
134 | static ::boost::type_traits::no_type is_convertible_to_Ret(...); // this version is used otherwise | |
135 | ||
136 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(is_convertible_to_Ret(BOOST_TT_TRAIT_OP make<Rhs>()))==sizeof(::boost::type_traits::yes_type))); | |
137 | }; | |
138 | ||
139 | ||
140 | // 5. checks for operator existence | |
141 | // condition: Rhs!=void | |
142 | ||
143 | // checks if our definition of operator BOOST_TT_TRAIT_OP is used or an other | |
144 | // existing one; | |
145 | // this is done with redefinition of "operator," that returns no_operator or has_operator | |
146 | struct has_operator { }; | |
147 | no_operator operator,(no_operator, has_operator); | |
148 | ||
149 | template < typename Rhs > | |
150 | struct operator_exists { | |
151 | static ::boost::type_traits::yes_type s_check(has_operator); // this version is preferred when operator exists | |
152 | static ::boost::type_traits::no_type s_check(no_operator); // this version is used otherwise | |
153 | ||
154 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(s_check(((BOOST_TT_TRAIT_OP make<Rhs>()),make<has_operator>())))==sizeof(::boost::type_traits::yes_type))); | |
155 | }; | |
156 | ||
157 | ||
158 | // 6. main trait: to avoid any compilation error, this class behaves | |
159 | // differently when operator BOOST_TT_TRAIT_OP(Rhs) is forbidden by the | |
160 | // standard. | |
161 | // Forbidden_if is a bool that is: | |
162 | // - true when the operator BOOST_TT_TRAIT_OP(Rhs) is forbidden by the standard | |
163 | // (would yield compilation error if used) | |
164 | // - false otherwise | |
165 | template < typename Rhs, typename Ret, bool Forbidden_if > | |
166 | struct trait_impl1; | |
167 | ||
168 | template < typename Rhs, typename Ret > | |
169 | struct trait_impl1 < Rhs, Ret, true > { | |
170 | BOOST_STATIC_CONSTANT(bool, value = false); | |
171 | }; | |
172 | ||
173 | template < typename Rhs, typename Ret > | |
174 | struct trait_impl1 < Rhs, Ret, false > { | |
175 | BOOST_STATIC_CONSTANT(bool, | |
176 | value = (operator_exists < Rhs >::value && operator_returns_Ret < Rhs, Ret, operator_returns_void < Rhs >::value >::value)); | |
177 | }; | |
178 | ||
179 | // specialization needs to be declared for the special void case | |
180 | template < typename Ret > | |
181 | struct trait_impl1 < void, Ret, false > { | |
182 | BOOST_STATIC_CONSTANT(bool, value = false); | |
183 | }; | |
184 | ||
185 | // defines some typedef for convenience | |
186 | template < typename Rhs, typename Ret > | |
187 | struct trait_impl { | |
188 | typedef typename ::boost::remove_reference<Rhs>::type Rhs_noref; | |
189 | typedef typename ::boost::remove_cv<Rhs_noref>::type Rhs_nocv; | |
190 | typedef typename ::boost::remove_cv< typename ::boost::remove_reference< typename ::boost::remove_pointer<Rhs_noref>::type >::type >::type Rhs_noptr; | |
191 | BOOST_STATIC_CONSTANT(bool, value = (trait_impl1 < Rhs_noref, Ret, BOOST_TT_FORBIDDEN_IF >::value)); | |
192 | }; | |
193 | ||
194 | } // namespace impl | |
195 | } // namespace detail | |
196 | ||
197 | // this is the accessible definition of the trait to end user | |
198 | template <class Rhs, class Ret=::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::dont_care> | |
199 | struct BOOST_TT_TRAIT_NAME : public integral_constant<bool, (::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME, _impl)::trait_impl < Rhs, Ret >::value)>{}; | |
200 | ||
201 | } // namespace boost | |
202 | ||
203 | #if defined(BOOST_MSVC) | |
204 | # pragma warning ( pop ) | |
205 | #endif |