1 | |
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2 | // (C) Copyright Rani Sharoni 2003. |
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3 | // Use, modification and distribution are subject to the Boost Software License, |
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4 | // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at |
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5 | // http://www.boost.org/LICENSE_1_0.txt). |
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6 | // |
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7 | // See http://www.boost.org/libs/type_traits for most recent version including documentation. |
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8 | |
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9 | #ifndef BOOST_TT_IS_BASE_AND_DERIVED_HPP_INCLUDED |
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10 | #define BOOST_TT_IS_BASE_AND_DERIVED_HPP_INCLUDED |
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11 | |
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12 | #include <boost/type_traits/intrinsics.hpp> |
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13 | #ifndef BOOST_IS_BASE_OF |
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14 | #include <boost/type_traits/is_class.hpp> |
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15 | #include <boost/type_traits/is_same.hpp> |
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16 | #include <boost/type_traits/is_convertible.hpp> |
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17 | #include <boost/type_traits/detail/ice_and.hpp> |
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18 | #include <boost/config.hpp> |
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19 | #include <boost/static_assert.hpp> |
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20 | #endif |
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21 | #include <boost/type_traits/remove_cv.hpp> |
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22 | |
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23 | // should be the last #include |
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24 | #include <boost/type_traits/detail/bool_trait_def.hpp> |
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25 | |
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26 | namespace boost { |
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27 | |
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28 | namespace detail { |
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29 | |
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30 | #ifndef BOOST_IS_BASE_OF |
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31 | #if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x581)) \ |
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32 | && !BOOST_WORKAROUND(__SUNPRO_CC , <= 0x540) \ |
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33 | && !BOOST_WORKAROUND(__EDG_VERSION__, <= 243) \ |
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34 | && !BOOST_WORKAROUND(__DMC__, BOOST_TESTED_AT(0x840)) |
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35 | |
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36 | // The EDG version number is a lower estimate. |
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37 | // It is not currently known which EDG version |
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38 | // exactly fixes the problem. |
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39 | |
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40 | /************************************************************************* |
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41 | |
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42 | This version detects ambiguous base classes and private base classes |
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43 | correctly, and was devised by Rani Sharoni. |
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44 | |
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45 | Explanation by Terje Slettebo and Rani Sharoni. |
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46 | |
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47 | Let's take the multiple base class below as an example, and the following |
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48 | will also show why there's not a problem with private or ambiguous base |
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49 | class: |
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50 | |
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51 | struct B {}; |
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52 | struct B1 : B {}; |
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53 | struct B2 : B {}; |
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54 | struct D : private B1, private B2 {}; |
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55 | |
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56 | is_base_and_derived<B, D>::value; |
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57 | |
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58 | First, some terminology: |
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59 | |
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60 | SC - Standard conversion |
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61 | UDC - User-defined conversion |
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62 | |
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63 | A user-defined conversion sequence consists of an SC, followed by an UDC, |
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64 | followed by another SC. Either SC may be the identity conversion. |
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65 | |
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66 | When passing the default-constructed Host object to the overloaded check_sig() |
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67 | functions (initialization 8.5/14/4/3), we have several viable implicit |
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68 | conversion sequences: |
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69 | |
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70 | For "static no_type check_sig(B const volatile *, int)" we have the conversion |
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71 | sequences: |
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72 | |
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73 | C -> C const (SC - Qualification Adjustment) -> B const volatile* (UDC) |
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74 | C -> D const volatile* (UDC) -> B1 const volatile* / B2 const volatile* -> |
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75 | B const volatile* (SC - Conversion) |
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76 | |
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77 | For "static yes_type check_sig(D const volatile *, T)" we have the conversion |
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78 | sequence: |
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79 | |
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80 | C -> D const volatile* (UDC) |
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81 | |
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82 | According to 13.3.3.1/4, in context of user-defined conversion only the |
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83 | standard conversion sequence is considered when selecting the best viable |
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84 | function, so it only considers up to the user-defined conversion. For the |
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85 | first function this means choosing between C -> C const and C -> C, and it |
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86 | chooses the latter, because it's a proper subset (13.3.3.2/3/2) of the |
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87 | former. Therefore, we have: |
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88 | |
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89 | C -> D const volatile* (UDC) -> B1 const volatile* / B2 const volatile* -> |
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90 | B const volatile* (SC - Conversion) |
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91 | C -> D const volatile* (UDC) |
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92 | |
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93 | Here, the principle of the "shortest subsequence" applies again, and it |
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94 | chooses C -> D const volatile*. This shows that it doesn't even need to |
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95 | consider the multiple paths to B, or accessibility, as that possibility is |
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96 | eliminated before it could possibly cause ambiguity or access violation. |
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97 | |
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98 | If D is not derived from B, it has to choose between C -> C const -> B const |
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99 | volatile* for the first function, and C -> D const volatile* for the second |
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100 | function, which are just as good (both requires a UDC, 13.3.3.2), had it not |
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101 | been for the fact that "static no_type check_sig(B const volatile *, int)" is |
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102 | not templated, which makes C -> C const -> B const volatile* the best choice |
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103 | (13.3.3/1/4), resulting in "no". |
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104 | |
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105 | Also, if Host::operator B const volatile* hadn't been const, the two |
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106 | conversion sequences for "static no_type check_sig(B const volatile *, int)", in |
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107 | the case where D is derived from B, would have been ambiguous. |
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108 | |
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109 | See also |
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110 | http://groups.google.com/groups?selm=df893da6.0301280859.522081f7%40posting. |
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111 | google.com and links therein. |
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112 | |
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113 | *************************************************************************/ |
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114 | |
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115 | template <typename B, typename D> |
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116 | struct bd_helper |
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117 | { |
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118 | // |
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119 | // This VC7.1 specific workaround stops the compiler from generating |
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120 | // an internal compiler error when compiling with /vmg (thanks to |
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121 | // Aleksey Gurtovoy for figuring out the workaround). |
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122 | // |
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123 | #if !BOOST_WORKAROUND(BOOST_MSVC, == 1310) |
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124 | template <typename T> |
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125 | static type_traits::yes_type check_sig(D const volatile *, T); |
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126 | static type_traits::no_type check_sig(B const volatile *, int); |
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127 | #else |
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128 | static type_traits::yes_type check_sig(D const volatile *, long); |
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129 | static type_traits::no_type check_sig(B const volatile * const&, int); |
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130 | #endif |
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131 | }; |
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132 | |
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133 | template<typename B, typename D> |
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134 | struct is_base_and_derived_impl2 |
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135 | { |
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136 | #if BOOST_WORKAROUND(BOOST_MSVC_FULL_VER, >= 140050000) |
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137 | #pragma warning(push) |
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138 | #pragma warning(disable:6334) |
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139 | #endif |
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140 | // |
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141 | // May silently do the wrong thing with incomplete types |
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142 | // unless we trap them here: |
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143 | // |
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144 | BOOST_STATIC_ASSERT(sizeof(B) != 0); |
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145 | BOOST_STATIC_ASSERT(sizeof(D) != 0); |
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146 | |
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147 | struct Host |
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148 | { |
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149 | #if !BOOST_WORKAROUND(BOOST_MSVC, == 1310) |
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150 | operator B const volatile *() const; |
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151 | #else |
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152 | operator B const volatile * const&() const; |
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153 | #endif |
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154 | operator D const volatile *(); |
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155 | }; |
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156 | |
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157 | BOOST_STATIC_CONSTANT(bool, value = |
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158 | sizeof(bd_helper<B,D>::check_sig(Host(), 0)) == sizeof(type_traits::yes_type)); |
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159 | #if BOOST_WORKAROUND(BOOST_MSVC_FULL_VER, >= 140050000) |
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160 | #pragma warning(pop) |
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161 | #endif |
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162 | }; |
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163 | |
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164 | #else |
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165 | |
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166 | // |
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167 | // broken version: |
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168 | // |
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169 | template<typename B, typename D> |
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170 | struct is_base_and_derived_impl2 |
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171 | { |
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172 | BOOST_STATIC_CONSTANT(bool, value = |
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173 | (::boost::is_convertible<D*,B*>::value)); |
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174 | }; |
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175 | |
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176 | #define BOOST_BROKEN_IS_BASE_AND_DERIVED |
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177 | |
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178 | #endif |
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179 | |
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180 | template <typename B, typename D> |
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181 | struct is_base_and_derived_impl3 |
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182 | { |
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183 | BOOST_STATIC_CONSTANT(bool, value = false); |
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184 | }; |
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185 | |
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186 | template <bool ic1, bool ic2, bool iss> |
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187 | struct is_base_and_derived_select |
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188 | { |
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189 | template <class T, class U> |
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190 | struct rebind |
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191 | { |
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192 | typedef is_base_and_derived_impl3<T,U> type; |
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193 | }; |
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194 | }; |
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195 | |
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196 | template <> |
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197 | struct is_base_and_derived_select<true,true,false> |
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198 | { |
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199 | template <class T, class U> |
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200 | struct rebind |
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201 | { |
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202 | typedef is_base_and_derived_impl2<T,U> type; |
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203 | }; |
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204 | }; |
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205 | |
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206 | template <typename B, typename D> |
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207 | struct is_base_and_derived_impl |
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208 | { |
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209 | typedef typename remove_cv<B>::type ncvB; |
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210 | typedef typename remove_cv<D>::type ncvD; |
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211 | |
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212 | typedef is_base_and_derived_select< |
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213 | ::boost::is_class<B>::value, |
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214 | ::boost::is_class<D>::value, |
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215 | ::boost::is_same<ncvB,ncvD>::value> selector; |
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216 | typedef typename selector::template rebind<ncvB,ncvD> binder; |
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217 | typedef typename binder::type bound_type; |
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218 | |
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219 | BOOST_STATIC_CONSTANT(bool, value = bound_type::value); |
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220 | }; |
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221 | #else |
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222 | template <typename B, typename D> |
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223 | struct is_base_and_derived_impl |
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224 | { |
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225 | typedef typename remove_cv<B>::type ncvB; |
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226 | typedef typename remove_cv<D>::type ncvD; |
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227 | |
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228 | BOOST_STATIC_CONSTANT(bool, value = (BOOST_IS_BASE_OF(B,D) && ! ::boost::is_same<ncvB,ncvD>::value)); |
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229 | }; |
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230 | #endif |
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231 | } // namespace detail |
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232 | |
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233 | BOOST_TT_AUX_BOOL_TRAIT_DEF2( |
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234 | is_base_and_derived |
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235 | , Base |
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236 | , Derived |
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237 | , (::boost::detail::is_base_and_derived_impl<Base,Derived>::value) |
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238 | ) |
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239 | |
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240 | #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION |
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241 | BOOST_TT_AUX_BOOL_TRAIT_PARTIAL_SPEC2_2(typename Base,typename Derived,is_base_and_derived,Base&,Derived,false) |
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242 | BOOST_TT_AUX_BOOL_TRAIT_PARTIAL_SPEC2_2(typename Base,typename Derived,is_base_and_derived,Base,Derived&,false) |
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243 | BOOST_TT_AUX_BOOL_TRAIT_PARTIAL_SPEC2_2(typename Base,typename Derived,is_base_and_derived,Base&,Derived&,false) |
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244 | #endif |
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245 | |
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246 | #if BOOST_WORKAROUND(__CODEGEARC__, BOOST_TESTED_AT(0x610)) |
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247 | BOOST_TT_AUX_BOOL_TRAIT_PARTIAL_SPEC2_1(typename Base,is_base_and_derived,Base,Base,false) |
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248 | #endif |
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249 | |
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250 | } // namespace boost |
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251 | |
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252 | #include <boost/type_traits/detail/bool_trait_undef.hpp> |
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253 | |
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254 | #endif // BOOST_TT_IS_BASE_AND_DERIVED_HPP_INCLUDED |
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