[Boost-commit] svn:boost r64997 - in sandbox/chrono/boost/type_traits: . detail

Subject: [Boost-commit] svn:boost r64997 - in sandbox/chrono/boost/type_traits: . detail
From: vicente.botet_at_[hidden]
Date: 2010-08-25 11:38:52

Author: viboes
Date: 2010-08-25 11:38:50 EDT (Wed, 25 Aug 2010)
New Revision: 64997
URL: http://svn.boost.org/trac/boost/changeset/64997

Log:
Towards implementing common_type without Typeof support
Added:
   sandbox/chrono/boost/type_traits/detail/
   sandbox/chrono/boost/type_traits/detail/common_type.hpp   (contents, props changed)
Text files modified: 
   sandbox/chrono/boost/type_traits/common_type.hpp |     8 +++++++-                                
   1 files changed, 7 insertions(+), 1 deletions(-)

Modified: sandbox/chrono/boost/type_traits/common_type.hpp
==============================================================================
--- sandbox/chrono/boost/type_traits/common_type.hpp	(original)
+++ sandbox/chrono/boost/type_traits/common_type.hpp	2010-08-25 11:38:50 EDT (Wed, 25 Aug 2010)
@@ -45,10 +45,12 @@
 #define BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE "must be complete type"
 #endif
 
+#include <boost/type_traits/detail/common_type.hpp>
 #include <boost/mpl/if.hpp>
 #include <boost/type_traits/is_void.hpp>
 #include <boost/type_traits/is_reference.hpp>
 #include <boost/type_traits/is_pointer.hpp>
+#include <boost/type_traits/remove_cv.hpp>
 
 //----------------------------------------------------------------------------//
 //                                                                            //
@@ -170,7 +172,11 @@
     template <class T, class U>
     struct common_type<T, U, void>
 #endif
-    : type_traits_detail::common_type_2<T,U>
+    //~ : type_traits_detail::common_type_2<T,U>
+    : detail_type_traits_common_type::common_type_impl<
+          typename remove_cv<T>::type,
+          typename remove_cv<U>::type
+      >
     { };
 
 

Added: sandbox/chrono/boost/type_traits/detail/common_type.hpp
==============================================================================
--- (empty file)
+++ sandbox/chrono/boost/type_traits/detail/common_type.hpp	2010-08-25 11:38:50 EDT (Wed, 25 Aug 2010)
@@ -0,0 +1,324 @@
+/*******************************************************************************
+ * boost/type_traits/detail/common_type.hpp
+ *
+ * Copyright 2010, Jeffrey Hellrung.
+ * Distributed under the Boost Software License, Version 1.0.  (See accompanying
+ * file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ *
+ * struct boost::common_type<T,U>
+ *
+ * common_type<T,U>::type is the type of the expression
+ *     b() ? x() : y()
+ * where b() returns a bool, x() has return type T, and y() has return type U.
+ * See
+ *     http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2661.htm#common_type
+ *
+ * Note that this evaluates to void if one or both of T and U is void.
+ ******************************************************************************/
+
+#ifndef BOOST_TYPE_TRAITS_DETAIL_COMMON_TYPE_HPP
+#define BOOST_TYPE_TRAITS_DETAIL_COMMON_TYPE_HPP
+
+#include <cstddef>
+
+#include <boost/mpl/assert.hpp>
+#include <boost/mpl/at.hpp>
+#include <boost/mpl/begin_end.hpp>
+#include <boost/mpl/contains.hpp>
+#include <boost/mpl/copy.hpp>
+#include <boost/mpl/deref.hpp>
+#include <boost/mpl/eval_if.hpp>
+#include <boost/mpl/if.hpp>
+#include <boost/mpl/inserter.hpp>
+#include <boost/mpl/next.hpp>
+#include <boost/mpl/or.hpp>
+#include <boost/mpl/placeholders.hpp>
+#include <boost/mpl/push_back.hpp>
+#include <boost/mpl/size.hpp>
+#include <boost/mpl/vector/vector0.hpp>
+#include <boost/mpl/vector/vector10.hpp>
+#include <boost/type_traits/integral_constant.hpp>
+#include <boost/type_traits/is_enum.hpp>
+#include <boost/type_traits/is_integral.hpp>
+#include <boost/type_traits/make_signed.hpp>
+#include <boost/type_traits/make_unsigned.hpp>
+#include <boost/type_traits/remove_cv.hpp>
+#include <boost/type_traits/remove_reference.hpp>
+
+namespace boost
+{
+
+namespace detail_type_traits_common_type
+{
+
+/*******************************************************************************
+ * struct propagate_cv< From, To >
+ *
+ * This metafunction propagates cv-qualifiers on type From to type To.
+ ******************************************************************************/
+
+template< class From, class To >
+struct propagate_cv
+{ typedef To type; };
+template< class From, class To >
+struct propagate_cv< const From, To >
+{ typedef To const type; };
+template< class From, class To >
+struct propagate_cv< volatile From, To >
+{ typedef To volatile type; };
+template< class From, class To >
+struct propagate_cv< const volatile From, To >
+{ typedef To const volatile type; };
+
+/*******************************************************************************
+ * struct is_signable_integral<T>
+ *
+ * This metafunction determines if T is an integral type which can be made
+ * signed or unsigned.
+ ******************************************************************************/
+
+template< class T >
+struct is_signable_integral
+    : mpl::or_< is_integral<T>, is_enum<T> >
+{ };
+template<>
+struct is_signable_integral< bool >
+    : false_type
+{ };
+
+/*******************************************************************************
+ * anon_obj<T>() -> T
+ *
+ * This dummy function only serves to generate an expression of type T.  This
+ * will be an rvalue expression if T is a non-reference type, and will be an
+ * lvalue expression if T is a reference type.
+ ******************************************************************************/
+
+template< class T > T anon_obj();
+
+/*******************************************************************************
+ * struct sizeof_t<N>
+ * typedef ... yes_type
+ * typedef ... no_type
+ *
+ * These types are integral players in the use of the "sizeof trick", i.e., we
+ * can distinguish overload selection by inspecting the size of the return type
+ * of the overload.
+ ******************************************************************************/
+
+template< std::size_t N > struct sizeof_t { char _dummy[N]; };
+typedef sizeof_t<1> yes_type;
+typedef sizeof_t<2> no_type;
+BOOST_MPL_ASSERT_RELATION( sizeof( yes_type ), ==, 1 );
+BOOST_MPL_ASSERT_RELATION( sizeof( no_type ), ==, 2 );
+
+/*******************************************************************************
+ * rvalue_test(T&) -> no_type
+ * rvalue_test(...) -> yes_type
+ *
+ * These overloads are used to determine the rvalue-ness of an expression.
+ ******************************************************************************/
+
+template< class T > no_type rvalue_test(T&);
+yes_type rvalue_test(...);
+
+/*******************************************************************************
+ * struct conversion_test_overloads< Sequence >
+ *
+ * This struct has multiple overloads of the static member function apply, each
+ * one taking a single parameter of a type within the Boost.MPL sequence
+ * Sequence.  Each such apply overload has a return type with sizeof equal to
+ * one plus the index of the parameter type within Sequence.  Thus, we can
+ * deduce the type T of an expression as long as we can generate a finite set of
+ * candidate types containing T via these apply overloads and the "sizeof
+ * trick".
+ ******************************************************************************/
+
+template< class First, class Last, std::size_t Index >
+struct conversion_test_overloads_iterate
+    : conversion_test_overloads_iterate<
+          typename mpl::next< First >::type, Last, Index + 1
+      >
+{
+    using conversion_test_overloads_iterate<
+        typename mpl::next< First >::type, Last, Index + 1
+    >::apply;
+    static sizeof_t< Index + 1 >
+    apply(typename mpl::deref< First >::type);
+};
+
+template< class Last, std::size_t Index >
+struct conversion_test_overloads_iterate< Last, Last, Index >
+{ static sizeof_t< Index + 1 > apply(...); };
+
+template< class Sequence >
+struct conversion_test_overloads
+    : conversion_test_overloads_iterate<
+          typename mpl::begin< Sequence >::type,
+          typename mpl::end< Sequence >::type,
+          0
+      >
+{ };
+
+/*******************************************************************************
+ * struct select< Sequence, Index >
+ *
+ * select is synonymous with mpl::at_c unless Index equals the size of the
+ * Boost.MPL Sequence, in which case this evaluates to void.
+ ******************************************************************************/
+
+template<
+    class Sequence, int Index,
+    int N = mpl::size< Sequence >::value
+>
+struct select
+    : mpl::at_c< Sequence, Index >
+{ };
+template< class Sequence, int N >
+struct select< Sequence, N, N >
+{ typedef void type; };
+
+/*******************************************************************************
+ * class deduce_common_type< T, U, NominalCandidates >
+ * struct nominal_candidates<T,U>
+ * struct common_type_dispatch_on_rvalueness<T,U>
+ * struct common_type_impl<T,U>
+ *
+ * These classes and structs implement the logic behind common_type, which goes
+ * roughly as follows.  Let C be the type of the conditional expression
+ *     anon_obj< bool >() ? anon_obj<T>() : anon_obj<U>()
+ * if C is an rvalue, then:
+ *     let T' and U' be T and U stripped of reference- and cv-qualifiers
+ *     if T' and U' are pointer types, say, T' = V* and U' = W*, then:
+ *         define the set of NominalCandidates to be
+ *             { V*, W*, V'*, W'* }
+ *           where V' is V with whatever cv-qualifiers are on W, and W' is W
+ *           with whatever cv-qualifiers are on V
+ *     else T' and U' are both "signable integral types" (integral and enum
+ *       types excepting bool), then:
+ *         define the set of NominalCandidates to be
+ *             { unsigned(T'), unsigned(U'), signed(T'), signed(U') }
+ *           where unsigned(X) is make_unsigned<X>::type and signed(X) is
+ *           make_signed<X>::type
+ *     else
+ *         define the set of NominalCandidates to be
+ *             { T', U' }
+ * else
+ *     let V and W be T and U stripped of reference-qualifiers
+ *     define the set of NominalCandidates to be
+ *         { V&, W&, V'&, W'& }
+ *     where V' is V with whatever cv-qualifiers are on W, and W' is W with
+ *       whatever cv-qualifiers are on V
+ * define the set of Candidates to be equal to the set of NominalCandidates with
+ * duplicates removed, and use this set of Candidates to determine C using the
+ * conversion_test_overloads struct
+ ******************************************************************************/
+
+template< class T, class U, class NominalCandidates >
+class deduce_common_type
+{
+    typedef typename mpl::copy<
+        NominalCandidates,
+        mpl::inserter<
+            mpl::vector0<>,
+            mpl::if_<
+                mpl::contains< mpl::_1, mpl::_2 >,
+                mpl::_1,
+                mpl::push_back< mpl::_1, mpl::_2 >
+            >
+        >
+    >::type candidate_types;
+    static const int best_candidate_index =
+        sizeof( conversion_test_overloads< candidate_types >::apply(
+            anon_obj< bool >() ? anon_obj<T>() : anon_obj<U>()
+        ) ) - 1;
+public:
+    typedef typename select< candidate_types, best_candidate_index >::type type;
+};
+
+template<
+    class T, class U,
+    class V = typename remove_cv< typename remove_reference<T>::type >::type,
+    class W = typename remove_cv< typename remove_reference<U>::type >::type,
+    bool = is_signable_integral<V>::value && is_signable_integral<W>::value
+>
+struct nominal_candidates;
+
+template< class T, class U, class V, class W >
+struct nominal_candidates< T, U, V, W, false >
+{ typedef mpl::vector2<V,W> type; };
+
+template< class T, class U, class V, class W >
+struct nominal_candidates< T, U, V, W, true >
+{
+    typedef mpl::vector4<
+        typename make_unsigned<V>::type,
+        typename make_unsigned<W>::type,
+        typename make_signed<V>::type,
+        typename make_signed<W>::type
+    > type;
+};
+
+template< class T, class U, class V, class W >
+struct nominal_candidates< T, U, V*, W*, false >
+{
+    typedef mpl::vector4<
+        V*, W*,
+        typename propagate_cv<W,V>::type *,
+        typename propagate_cv<V,W>::type *
+    > type;
+};
+
+template<
+    class T, class U,
+    bool = sizeof( ::boost::detail_type_traits_common_type::rvalue_test(
+        anon_obj< bool >() ? anon_obj<T>() : anon_obj<U>()
+    ) ) == sizeof( yes_type )
+>
+struct common_type_dispatch_on_rvalueness;
+
+template< class T, class U >
+struct common_type_dispatch_on_rvalueness< T, U, true >
+    : deduce_common_type< T, U, typename nominal_candidates<T,U>::type >
+{ };
+
+template< class T, class U >
+struct common_type_dispatch_on_rvalueness< T, U, false >
+{
+private:
+    typedef typename remove_reference<T>::type unrefed_T_type;
+    typedef typename remove_reference<U>::type unrefed_U_type;
+public:
+    typedef typename deduce_common_type<
+        T, U,
+        mpl::vector4<
+            unrefed_T_type &,
+            unrefed_U_type &,
+            typename propagate_cv< unrefed_U_type, unrefed_T_type >::type &,
+            typename propagate_cv< unrefed_T_type, unrefed_U_type >::type &
+        >
+    >::type type;
+};
+
+template< class T, class U >
+struct common_type_impl
+    : common_type_dispatch_on_rvalueness<T,U>
+{ };
+
+template< class T > struct common_type_impl< T, void > { typedef void type; };
+template< class T > struct common_type_impl< void, T > { typedef void type; };
+template<> struct common_type_impl< void, void > { typedef void type; };
+
+} // namespace detail_type_traits_common_type
+
+//~ template< class T, class U >
+//~ struct common_type
+    //~ : detail_type_traits_common_type::common_type_impl<
+          //~ typename remove_cv<T>::type,
+          //~ typename remove_cv<U>::type
+      //~ >
+//~ { };
+
+} // namespace boost
+
+#endif // #ifndef BOOST_TYPE_TRAITS_COMMON_TYPE_HPP