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_pointer.hpp> |
15 | #include <boost/type_traits/is_same.hpp> |
16 | #include <boost/type_traits/is_void.hpp> |
17 | #include <boost/type_traits/remove_cv.hpp> |
18 | #include <boost/type_traits/remove_pointer.hpp> |
19 | #include <boost/type_traits/remove_reference.hpp> |
20 | |
21 | // avoid warnings |
22 | #if defined(__GNUC__) |
23 | # pragma GCC system_header |
24 | #elif defined(BOOST_MSVC) |
25 | # pragma warning ( push ) |
26 | # pragma warning ( disable : 4244 4913) |
27 | # if BOOST_WORKAROUND(BOOST_MSVC_FULL_VER, >= 140050000) |
28 | # pragma warning ( disable : 6334) |
29 | # endif |
30 | #endif |
31 | |
32 | namespace boost { |
33 | namespace detail { |
34 | |
35 | // This namespace ensures that argument-dependent name lookup does not mess things up. |
36 | namespace BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl) { |
37 | |
38 | // 1. a function to have an instance of type T without requiring T to be default |
39 | // constructible |
40 | template <typename T> T &make(); |
41 | |
42 | |
43 | // 2. we provide our operator definition for types that do not have one already |
44 | |
45 | // a type returned from operator BOOST_TT_TRAIT_OP when no such operator is |
46 | // found in the type's own namespace (our own operator is used) so that we have |
47 | // a means to know that our operator was used |
48 | struct no_operator { }; |
49 | |
50 | // this class allows implicit conversions and makes the following operator |
51 | // definition less-preferred than any other such operators that might be found |
52 | // via argument-dependent name lookup |
53 | struct any { template <class T> any(T const&); }; |
54 | |
55 | // when operator BOOST_TT_TRAIT_OP is not available, this one is used |
56 | no_operator operator BOOST_TT_TRAIT_OP (const any&, int); |
57 | |
58 | |
59 | // 3. checks if the operator returns void or not |
60 | // conditions: Lhs!=void |
61 | |
62 | // we first redefine "operator," so that we have no compilation error if |
63 | // operator BOOST_TT_TRAIT_OP returns void and we can use the return type of |
64 | // (lhs BOOST_TT_TRAIT_OP, returns_void_t()) to deduce if |
65 | // operator BOOST_TT_TRAIT_OP returns void or not: |
66 | // - operator BOOST_TT_TRAIT_OP returns void -> (lhs BOOST_TT_TRAIT_OP, returns_void_t()) returns returns_void_t |
67 | // - operator BOOST_TT_TRAIT_OP returns !=void -> (lhs BOOST_TT_TRAIT_OP, returns_void_t()) returns int |
68 | struct returns_void_t { }; |
69 | template <typename T> int operator,(const T&, returns_void_t); |
70 | template <typename T> int operator,(const volatile T&, returns_void_t); |
71 | |
72 | // this intermediate trait has member value of type bool: |
73 | // - value==true -> operator BOOST_TT_TRAIT_OP returns void |
74 | // - value==false -> operator BOOST_TT_TRAIT_OP does not return void |
75 | template < typename Lhs > |
76 | struct operator_returns_void { |
77 | // overloads of function returns_void make the difference |
78 | // yes_type and no_type have different size by construction |
79 | static ::boost::type_traits::yes_type returns_void(returns_void_t); |
80 | static ::boost::type_traits::no_type returns_void(int); |
81 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(::boost::type_traits::yes_type)==sizeof(returns_void((make<Lhs>() BOOST_TT_TRAIT_OP,returns_void_t()))))); |
82 | }; |
83 | |
84 | |
85 | // 4. checks if the return type is Ret or Ret==dont_care |
86 | // conditions: Lhs!=void |
87 | |
88 | struct dont_care { }; |
89 | |
90 | template < typename Lhs, typename Ret, bool Returns_void > |
91 | struct operator_returns_Ret; |
92 | |
93 | template < typename Lhs > |
94 | struct operator_returns_Ret < Lhs, dont_care, true > { |
95 | BOOST_STATIC_CONSTANT(bool, value = true); |
96 | }; |
97 | |
98 | template < typename Lhs > |
99 | struct operator_returns_Ret < Lhs, dont_care, false > { |
100 | BOOST_STATIC_CONSTANT(bool, value = true); |
101 | }; |
102 | |
103 | template < typename Lhs > |
104 | struct operator_returns_Ret < Lhs, void, true > { |
105 | BOOST_STATIC_CONSTANT(bool, value = true); |
106 | }; |
107 | |
108 | template < typename Lhs > |
109 | struct operator_returns_Ret < Lhs, void, false > { |
110 | BOOST_STATIC_CONSTANT(bool, value = false); |
111 | }; |
112 | |
113 | template < typename Lhs, typename Ret > |
114 | struct operator_returns_Ret < Lhs, Ret, true > { |
115 | BOOST_STATIC_CONSTANT(bool, value = false); |
116 | }; |
117 | |
118 | // otherwise checks if it is convertible to Ret using the sizeof trick |
119 | // based on overload resolution |
120 | // condition: Ret!=void and Ret!=dont_care and the operator does not return void |
121 | template < typename Lhs, typename Ret > |
122 | struct operator_returns_Ret < Lhs, Ret, false > { |
123 | static ::boost::type_traits::yes_type is_convertible_to_Ret(Ret); // this version is preferred for types convertible to Ret |
124 | static ::boost::type_traits::no_type is_convertible_to_Ret(...); // this version is used otherwise |
125 | |
126 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(is_convertible_to_Ret(make<Lhs>() BOOST_TT_TRAIT_OP))==sizeof(::boost::type_traits::yes_type))); |
127 | }; |
128 | |
129 | |
130 | // 5. checks for operator existence |
131 | // condition: Lhs!=void |
132 | |
133 | // checks if our definition of operator BOOST_TT_TRAIT_OP is used or an other |
134 | // existing one; |
135 | // this is done with redefinition of "operator," that returns no_operator or has_operator |
136 | struct has_operator { }; |
137 | no_operator operator,(no_operator, has_operator); |
138 | |
139 | template < typename Lhs > |
140 | struct operator_exists { |
141 | static ::boost::type_traits::yes_type s_check(has_operator); // this version is preferred when operator exists |
142 | static ::boost::type_traits::no_type s_check(no_operator); // this version is used otherwise |
143 | |
144 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(s_check(((make<Lhs>() BOOST_TT_TRAIT_OP),make<has_operator>())))==sizeof(::boost::type_traits::yes_type))); |
145 | }; |
146 | |
147 | |
148 | // 6. main trait: to avoid any compilation error, this class behaves |
149 | // differently when operator BOOST_TT_TRAIT_OP(Lhs) is forbidden by the |
150 | // standard. |
151 | // Forbidden_if is a bool that is: |
152 | // - true when the operator BOOST_TT_TRAIT_OP(Lhs) is forbidden by the standard |
153 | // (would yield compilation error if used) |
154 | // - false otherwise |
155 | template < typename Lhs, typename Ret, bool Forbidden_if > |
156 | struct trait_impl1; |
157 | |
158 | template < typename Lhs, typename Ret > |
159 | struct trait_impl1 < Lhs, Ret, true > { |
160 | BOOST_STATIC_CONSTANT(bool, value = false); |
161 | }; |
162 | |
163 | template < typename Lhs, typename Ret > |
164 | struct trait_impl1 < Lhs, Ret, false > { |
165 | BOOST_STATIC_CONSTANT(bool, |
166 | value = (operator_exists < Lhs >::value && operator_returns_Ret < Lhs, Ret, operator_returns_void < Lhs >::value >::value)); |
167 | }; |
168 | |
169 | // specialization needs to be declared for the special void case |
170 | template < typename Ret > |
171 | struct trait_impl1 < void, Ret, false > { |
172 | BOOST_STATIC_CONSTANT(bool, value = false); |
173 | }; |
174 | |
175 | // defines some typedef for convenience |
176 | template < typename Lhs, typename Ret > |
177 | struct trait_impl { |
178 | typedef typename ::boost::remove_reference<Lhs>::type Lhs_noref; |
179 | typedef typename ::boost::remove_cv<Lhs_noref>::type Lhs_nocv; |
180 | typedef typename ::boost::remove_cv< typename ::boost::remove_reference< typename ::boost::remove_pointer<Lhs_noref>::type >::type >::type Lhs_noptr; |
181 | BOOST_STATIC_CONSTANT(bool, value = (trait_impl1 < Lhs_noref, Ret, BOOST_TT_FORBIDDEN_IF >::value)); |
182 | }; |
183 | |
184 | } // namespace impl |
185 | } // namespace detail |
186 | |
187 | // this is the accessible definition of the trait to end user |
188 | template <class Lhs, class Ret=::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::dont_care> |
189 | struct BOOST_TT_TRAIT_NAME : public integral_constant<bool, (::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME, _impl)::trait_impl< Lhs, Ret >::value)>{}; |
190 | |
191 | } // namespace boost |
192 | |
193 | #if defined(BOOST_MSVC) |
194 | # pragma warning ( pop ) |
195 | #endif |
196 | |