1 // Copyright David Abrahams 2002.
2 // Distributed under the Boost Software License, Version 1.0. (See
3 // accompanying file LICENSE_1_0.txt or copy at
4 // http://www.boost.org/LICENSE_1_0.txt)
5 #ifndef BASES_DWA2002321_HPP
6 # define BASES_DWA2002321_HPP
7 
8 # include <boost/python/detail/prefix.hpp>
9 # include <boost/type_traits/object_traits.hpp>
10 # include <boost/python/detail/type_list.hpp>
11 # include <boost/mpl/if.hpp>
12 # include <boost/mpl/bool.hpp>
13 # include <boost/preprocessor/enum_params_with_a_default.hpp>
14 # include <boost/preprocessor/enum_params.hpp>
15 
16 namespace boost { namespace python {
17 
18 # define BOOST_PYTHON_BASE_PARAMS BOOST_PP_ENUM_PARAMS_Z(1, BOOST_PYTHON_MAX_BASES, Base)
19 
20   // A type list for specifying bases
21   template < BOOST_PP_ENUM_PARAMS_WITH_A_DEFAULT(BOOST_PYTHON_MAX_BASES, typename Base, mpl::void_) >
22   struct bases : detail::type_list< BOOST_PYTHON_BASE_PARAMS >::type
23   {};
24 
25   namespace detail
26   {
27 # ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
28     template <class T> struct specifies_bases
29         : mpl::false_
30     {
31     };
32 
33     template < BOOST_PP_ENUM_PARAMS_Z(1, BOOST_PYTHON_MAX_BASES, class Base) >
34     struct specifies_bases< bases< BOOST_PYTHON_BASE_PARAMS > >
35         : mpl::true_
36     {
37     };
38 # else
39     template < BOOST_PP_ENUM_PARAMS(BOOST_PYTHON_MAX_BASES, class Base) >
40     static char is_bases_helper(bases< BOOST_PYTHON_BASE_PARAMS > const&);
41 
42     static char (& is_bases_helper(...) )[256];
43 
44     template <class T>
45     struct specifies_bases
46     {
47      private:
48         static typename add_reference<T>::type make();
49         BOOST_STATIC_CONSTANT(bool, non_ref = !is_reference<T>::value);
50      public:
51         BOOST_STATIC_CONSTANT(bool, value = non_ref & (sizeof(is_bases_helper(make())) == 1));
52         typedef mpl::bool_<value> type;
53     };
54 # endif
55     template <class T, class Prev = bases<> >
56     struct select_bases
57         : mpl::if_<
58                 specifies_bases<T>
59                 , T
60                 , Prev
61           >
62     {
63     };
64   }
65 # undef BOOST_PYTHON_BASE_PARAMS
66 }} // namespace boost::python
67 
68 #endif // BASES_DWA2002321_HPP
69