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 |
206 | |