[857] | 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/is_class.hpp"
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| 13 | #include "boost/type_traits/is_same.hpp"
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| 14 | #include "boost/type_traits/is_convertible.hpp"
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| 15 | #include "boost/type_traits/detail/ice_and.hpp"
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| 16 | #include "boost/type_traits/remove_cv.hpp"
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| 17 | #include "boost/config.hpp"
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| 18 |
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| 19 | // should be the last #include
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| 20 | #include "boost/type_traits/detail/bool_trait_def.hpp"
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| 21 |
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| 22 | namespace boost {
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| 23 |
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| 24 | namespace detail {
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| 25 |
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| 26 | #if !BOOST_WORKAROUND(__BORLANDC__, <= 0x570) \
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| 27 | && !BOOST_WORKAROUND(__SUNPRO_CC , BOOST_TESTED_AT(0x540)) \
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| 28 | && !BOOST_WORKAROUND(__EDG_VERSION__, <= 243) \
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| 29 | && !BOOST_WORKAROUND(__DMC__, BOOST_TESTED_AT(0x840))
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| 30 |
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| 31 | // The EDG version number is a lower estimate.
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| 32 | // It is not currently known which EDG version
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| 33 | // exactly fixes the problem.
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| 34 |
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| 35 | /*************************************************************************
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| 36 |
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| 37 | This version detects ambiguous base classes and private base classes
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| 38 | correctly, and was devised by Rani Sharoni.
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| 39 |
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| 40 | Explanation by Terje Slettebø and Rani Sharoni.
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| 41 |
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| 42 | Let's take the multiple base class below as an example, and the following
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| 43 | will also show why there's not a problem with private or ambiguous base
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| 44 | class:
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| 45 |
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| 46 | struct B {};
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| 47 | struct B1 : B {};
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| 48 | struct B2 : B {};
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| 49 | struct D : private B1, private B2 {};
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| 50 |
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| 51 | is_base_and_derived<B, D>::value;
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| 52 |
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| 53 | First, some terminology:
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| 54 |
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| 55 | SC - Standard conversion
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| 56 | UDC - User-defined conversion
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| 57 |
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| 58 | A user-defined conversion sequence consists of an SC, followed by an UDC,
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| 59 | followed by another SC. Either SC may be the identity conversion.
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| 60 |
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| 61 | When passing the default-constructed Host object to the overloaded check_sig()
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| 62 | functions (initialization 8.5/14/4/3), we have several viable implicit
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| 63 | conversion sequences:
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| 64 |
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| 65 | For "static no_type check_sig(B const volatile *, int)" we have the conversion
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| 66 | sequences:
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| 67 |
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| 68 | C -> C const (SC - Qualification Adjustment) -> B const volatile* (UDC)
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| 69 | C -> D const volatile* (UDC) -> B1 const volatile* / B2 const volatile* ->
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| 70 | B const volatile* (SC - Conversion)
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| 71 |
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| 72 | For "static yes_type check_sig(D const volatile *, T)" we have the conversion
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| 73 | sequence:
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| 74 |
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| 75 | C -> D const volatile* (UDC)
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| 76 |
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| 77 | According to 13.3.3.1/4, in context of user-defined conversion only the
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| 78 | standard conversion sequence is considered when selecting the best viable
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| 79 | function, so it only considers up to the user-defined conversion. For the
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| 80 | first function this means choosing between C -> C const and C -> C, and it
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| 81 | chooses the latter, because it's a proper subset (13.3.3.2/3/2) of the
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| 82 | former. Therefore, we have:
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| 83 |
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| 84 | C -> D const volatile* (UDC) -> B1 const volatile* / B2 const volatile* ->
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| 85 | B const volatile* (SC - Conversion)
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| 86 | C -> D const volatile* (UDC)
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| 87 |
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| 88 | Here, the principle of the "shortest subsequence" applies again, and it
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| 89 | chooses C -> D const volatile*. This shows that it doesn't even need to
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| 90 | consider the multiple paths to B, or accessibility, as that possibility is
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| 91 | eliminated before it could possibly cause ambiguity or access violation.
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| 92 |
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| 93 | If D is not derived from B, it has to choose between C -> C const -> B const
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| 94 | volatile* for the first function, and C -> D const volatile* for the second
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| 95 | function, which are just as good (both requires a UDC, 13.3.3.2), had it not
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| 96 | been for the fact that "static no_type check_sig(B const volatile *, int)" is
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| 97 | not templated, which makes C -> C const -> B const volatile* the best choice
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| 98 | (13.3.3/1/4), resulting in "no".
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| 99 |
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| 100 | Also, if Host::operator B const volatile* hadn't been const, the two
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| 101 | conversion sequences for "static no_type check_sig(B const volatile *, int)", in
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| 102 | the case where D is derived from B, would have been ambiguous.
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| 103 |
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| 104 | See also
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| 105 | http://groups.google.com/groups?selm=df893da6.0301280859.522081f7%40posting.
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| 106 | google.com and links therein.
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| 107 |
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| 108 | *************************************************************************/
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| 109 |
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| 110 | template <typename B, typename D>
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| 111 | struct bd_helper
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| 112 | {
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| 113 | //
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| 114 | // This VC7.1 specific workaround stops the compiler from generating
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| 115 | // an internal compiler error when compiling with /vmg (thanks to
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| 116 | // Aleksey Gurtovoy for figuring out the workaround).
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| 117 | //
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| 118 | #if !BOOST_WORKAROUND(BOOST_MSVC, == 1310)
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| 119 | template <typename T>
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| 120 | static type_traits::yes_type check_sig(D const volatile *, T);
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| 121 | static type_traits::no_type check_sig(B const volatile *, int);
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| 122 | #else
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| 123 | static type_traits::yes_type check_sig(D const volatile *, long);
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| 124 | static type_traits::no_type check_sig(B const volatile * const&, int);
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| 125 | #endif
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| 126 | };
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| 127 |
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| 128 | template<typename B, typename D>
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| 129 | struct is_base_and_derived_impl2
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| 130 | {
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| 131 | struct Host
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| 132 | {
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| 133 | #if !BOOST_WORKAROUND(BOOST_MSVC, == 1310)
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| 134 | operator B const volatile *() const;
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| 135 | #else
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| 136 | operator B const volatile * const&() const;
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| 137 | #endif
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| 138 | operator D const volatile *();
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| 139 | };
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| 140 |
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| 141 | BOOST_STATIC_CONSTANT(bool, value =
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| 142 | sizeof(bd_helper<B,D>::check_sig(Host(), 0)) == sizeof(type_traits::yes_type));
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| 143 | };
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| 144 |
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| 145 | #else
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| 146 |
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| 147 | //
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| 148 | // broken version:
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| 149 | //
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| 150 | template<typename B, typename D>
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| 151 | struct is_base_and_derived_impl2
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| 152 | {
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| 153 | BOOST_STATIC_CONSTANT(bool, value =
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| 154 | (::boost::is_convertible<D*,B*>::value));
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| 155 | };
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| 156 |
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| 157 | #define BOOST_BROKEN_IS_BASE_AND_DERIVED
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| 158 |
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| 159 | #endif
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| 160 |
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| 161 | template <typename B, typename D>
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| 162 | struct is_base_and_derived_impl3
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| 163 | {
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| 164 | BOOST_STATIC_CONSTANT(bool, value = false);
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| 165 | };
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| 166 |
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| 167 | template <bool ic1, bool ic2, bool iss>
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| 168 | struct is_base_and_derived_select
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| 169 | {
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| 170 | template <class T, class U>
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| 171 | struct rebind
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| 172 | {
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| 173 | typedef is_base_and_derived_impl3<T,U> type;
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| 174 | };
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| 175 | };
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| 176 |
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| 177 | template <>
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| 178 | struct is_base_and_derived_select<true,true,false>
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| 179 | {
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| 180 | template <class T, class U>
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| 181 | struct rebind
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| 182 | {
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| 183 | typedef is_base_and_derived_impl2<T,U> type;
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| 184 | };
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| 185 | };
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| 186 |
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| 187 | template <typename B, typename D>
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| 188 | struct is_base_and_derived_impl
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| 189 | {
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| 190 | typedef typename remove_cv<B>::type ncvB;
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| 191 | typedef typename remove_cv<D>::type ncvD;
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| 192 |
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| 193 | typedef is_base_and_derived_select<
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| 194 | ::boost::is_class<B>::value,
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| 195 | ::boost::is_class<D>::value,
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| 196 | ::boost::is_same<B,D>::value> selector;
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| 197 | typedef typename selector::template rebind<ncvB,ncvD> binder;
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| 198 | typedef typename binder::type bound_type;
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| 199 |
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| 200 | BOOST_STATIC_CONSTANT(bool, value = bound_type::value);
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| 201 | };
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| 202 |
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| 203 | } // namespace detail
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| 204 |
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| 205 | BOOST_TT_AUX_BOOL_TRAIT_DEF2(
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| 206 | is_base_and_derived
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| 207 | , Base
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| 208 | , Derived
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| 209 | , (::boost::detail::is_base_and_derived_impl<Base,Derived>::value)
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| 210 | )
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| 211 |
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| 212 | #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
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| 213 | BOOST_TT_AUX_BOOL_TRAIT_PARTIAL_SPEC2_2(typename Base,typename Derived,is_base_and_derived,Base&,Derived,false)
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| 214 | BOOST_TT_AUX_BOOL_TRAIT_PARTIAL_SPEC2_2(typename Base,typename Derived,is_base_and_derived,Base,Derived&,false)
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| 215 | BOOST_TT_AUX_BOOL_TRAIT_PARTIAL_SPEC2_2(typename Base,typename Derived,is_base_and_derived,Base&,Derived&,false)
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| 216 | #endif
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| 217 |
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| 218 | } // namespace boost
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| 219 |
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| 220 | #include "boost/type_traits/detail/bool_trait_undef.hpp"
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| 221 |
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| 222 | #endif // BOOST_TT_IS_BASE_AND_DERIVED_HPP_INCLUDED
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