source: NonGTP/Boost/boost/variant/detail/visitation_impl.hpp @ 857

Revision 857, 8.6 KB checked in by igarcia, 19 years ago (diff)
RevLine 
[857]1//-----------------------------------------------------------------------------
2// boost variant/detail/visitation_impl.hpp header file
3// See http://www.boost.org for updates, documentation, and revision history.
4//-----------------------------------------------------------------------------
5//
6// Copyright (c) 2003
7// Eric Friedman
8//
9// Distributed under the Boost Software License, Version 1.0. (See
10// accompanying file LICENSE_1_0.txt or copy at
11// http://www.boost.org/LICENSE_1_0.txt)
12
13#ifndef BOOST_VARIANT_DETAIL_VISITATION_IMPL_HPP
14#define BOOST_VARIANT_DETAIL_VISITATION_IMPL_HPP
15
16#include "boost/config.hpp"
17
18#include "boost/variant/detail/backup_holder.hpp"
19#include "boost/variant/detail/cast_storage.hpp"
20#include "boost/variant/detail/forced_return.hpp"
21#include "boost/variant/detail/generic_result_type.hpp"
22
23#include "boost/assert.hpp"
24#include "boost/mpl/eval_if.hpp"
25#include "boost/mpl/bool.hpp"
26#include "boost/mpl/identity.hpp"
27#include "boost/mpl/int.hpp"
28#include "boost/mpl/next.hpp"
29#include "boost/mpl/deref.hpp"
30#include "boost/mpl/or.hpp"
31#include "boost/preprocessor/cat.hpp"
32#include "boost/preprocessor/inc.hpp"
33#include "boost/preprocessor/repeat.hpp"
34#include "boost/type_traits/is_same.hpp"
35#include "boost/type_traits/has_nothrow_copy.hpp"
36#include "boost/variant/detail/has_nothrow_move.hpp"
37
38
39///////////////////////////////////////////////////////////////////////////////
40// BOOST_VARIANT_VISITATION_UNROLLING_LIMIT
41//
42// Unrolls variant's visitation mechanism to reduce template instantiation
43// and potentially increase runtime performance. (TODO: Investigate further.)
44//
45#if !defined(BOOST_VARIANT_VISITATION_UNROLLING_LIMIT)
46#   define BOOST_VARIANT_VISITATION_UNROLLING_LIMIT   \
47        BOOST_VARIANT_LIMIT_TYPES
48#endif
49
50namespace boost {
51namespace detail { namespace variant {
52
53///////////////////////////////////////////////////////////////////////////////
54// (detail) class apply_visitor_unrolled
55//
56// Tag type indicates when visitation_impl is unrolled.
57//
58struct apply_visitor_unrolled {};
59
60///////////////////////////////////////////////////////////////////////////////
61// (detail) class template visitation_impl_step
62//
63// "Never ending" iterator range facilitates visitation_impl unrolling.
64//
65
66#if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
67
68template <typename Iter, typename LastIter>
69struct visitation_impl_step
70{
71    typedef typename mpl::deref<Iter>::type type;
72
73    typedef typename mpl::next<Iter>::type next_iter;
74    typedef visitation_impl_step<
75          next_iter, LastIter
76        > next;
77};
78
79template <typename LastIter>
80struct visitation_impl_step< LastIter,LastIter >
81{
82    typedef apply_visitor_unrolled type;
83    typedef visitation_impl_step next;
84};
85
86#else // defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
87
88template <typename Iter, typename LastIter>
89struct visitation_impl_step
90{
91    typedef typename mpl::eval_if<
92          is_same<Iter, LastIter>
93        , mpl::identity<apply_visitor_unrolled>
94        , Iter
95        >::type type;
96
97    typedef typename mpl::eval_if<
98          is_same<type, apply_visitor_unrolled> //is_same<Iter, LastIter>
99        , mpl::identity<LastIter>
100        , mpl::next<Iter>
101        >::type next_iter;
102
103    typedef visitation_impl_step<
104          next_iter, LastIter
105        > next;
106};
107
108#endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION workaround
109
110///////////////////////////////////////////////////////////////////////////////
111// (detail) function template visitation_impl_invoke
112//
113// Invokes the given visitor on the specified type in the given storage.
114//
115
116template <typename Visitor, typename VoidPtrCV, typename T>
117inline
118    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)
119visitation_impl_invoke_impl(
120      int, Visitor& visitor, VoidPtrCV storage, T*
121    , mpl::true_// never_uses_backup
122    )
123{
124    return visitor.internal_visit(
125          cast_storage<T>(storage), 1L
126        );
127}
128
129template <typename Visitor, typename VoidPtrCV, typename T>
130inline
131    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)
132visitation_impl_invoke_impl(
133      int internal_which, Visitor& visitor, VoidPtrCV storage, T*
134    , mpl::false_// never_uses_backup
135    )
136{
137    if (internal_which >= 0)
138    {
139        return visitor.internal_visit(
140              cast_storage<T>(storage), 1L
141            );
142    }
143    else
144    {
145        return visitor.internal_visit(
146              cast_storage< backup_holder<T> >(storage), 1L
147            );
148    }
149}
150
151template <typename Visitor, typename VoidPtrCV, typename T, typename NoBackupFlag>
152inline
153    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)
154visitation_impl_invoke(
155      int internal_which, Visitor& visitor, VoidPtrCV storage, T* t
156    , NoBackupFlag
157    , int
158    )
159{
160    typedef typename mpl::or_<
161          NoBackupFlag
162        , has_nothrow_move_constructor<T>
163        , has_nothrow_copy<T>
164        >::type never_uses_backup;
165
166    return visitation_impl_invoke_impl(
167          internal_which, visitor, storage, t
168        , never_uses_backup()
169        );
170}
171
172template <typename Visitor, typename VoidPtrCV, typename NBF>
173inline
174    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)
175visitation_impl_invoke(int, Visitor&, VoidPtrCV, apply_visitor_unrolled*, NBF, long)
176{
177    // should never be here at runtime:
178    BOOST_ASSERT(false);
179    typedef typename Visitor::result_type result_type;
180    return ::boost::detail::variant::forced_return< result_type >();
181}
182
183///////////////////////////////////////////////////////////////////////////////
184// (detail) function template visitation_impl
185//
186// Invokes the given visitor on the type in the given variant storage.
187//
188
189template <
190      typename W, typename S
191    , typename Visitor, typename VPCV
192    , typename NBF
193    >
194inline
195    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)
196visitation_impl(
197      int, int, Visitor&, VPCV
198    , mpl::true_ // is_apply_visitor_unrolled
199    , NBF, W* = 0, S* = 0
200    )
201{
202    // should never be here at runtime:
203    BOOST_ASSERT(false);
204    typedef typename Visitor::result_type result_type;
205    return ::boost::detail::variant::forced_return< result_type >();
206}
207
208template <
209      typename Which, typename step0
210    , typename Visitor, typename VoidPtrCV
211    , typename NoBackupFlag
212    >
213inline
214    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)
215visitation_impl(
216      const int internal_which, const int logical_which
217    , Visitor& visitor, VoidPtrCV storage
218    , mpl::false_ // is_apply_visitor_unrolled
219    , NoBackupFlag no_backup_flag
220    , Which* = 0, step0* = 0
221    )
222{
223    // Typedef apply_visitor_unrolled steps and associated types...
224#   define BOOST_VARIANT_AUX_APPLY_VISITOR_STEP_TYPEDEF(z, N, _) \
225    typedef typename BOOST_PP_CAT(step,N)::type BOOST_PP_CAT(T,N); \
226    typedef typename BOOST_PP_CAT(step,N)::next \
227        BOOST_PP_CAT(step, BOOST_PP_INC(N)); \
228    /**/
229
230    BOOST_PP_REPEAT(
231          BOOST_VARIANT_VISITATION_UNROLLING_LIMIT
232        , BOOST_VARIANT_AUX_APPLY_VISITOR_STEP_TYPEDEF
233        , _
234        )
235
236#   undef BOOST_VARIANT_AUX_APPLY_VISITOR_STEP_TYPEDEF
237
238    // ...switch on the target which-index value...
239    switch (logical_which)
240    {
241
242    // ...applying the appropriate case:
243#   define BOOST_VARIANT_AUX_APPLY_VISITOR_STEP_CASE(z, N, _) \
244    case (Which::value + (N)): \
245        return visitation_impl_invoke( \
246              internal_which, visitor, storage \
247            , static_cast<BOOST_PP_CAT(T,N)*>(0) \
248            , no_backup_flag, 1L \
249            ); \
250    /**/
251
252    BOOST_PP_REPEAT(
253          BOOST_VARIANT_VISITATION_UNROLLING_LIMIT
254        , BOOST_VARIANT_AUX_APPLY_VISITOR_STEP_CASE
255        , _
256        )
257
258#   undef BOOST_VARIANT_AUX_APPLY_VISITOR_STEP_CASE
259
260    }
261
262    // If not handled in this iteration, continue unrolling:
263    typedef mpl::int_<
264          Which::value + (BOOST_VARIANT_VISITATION_UNROLLING_LIMIT)
265        > next_which;
266
267    typedef BOOST_PP_CAT(step, BOOST_VARIANT_VISITATION_UNROLLING_LIMIT)
268        next_step;
269
270    typedef typename next_step::type next_type;
271    typedef typename is_same< next_type,apply_visitor_unrolled >::type
272        is_apply_visitor_unrolled;
273
274    return visitation_impl(
275          internal_which, logical_which
276        , visitor, storage
277        , is_apply_visitor_unrolled()
278        , no_backup_flag
279        , static_cast<next_which*>(0), static_cast<next_step*>(0)
280        );
281}
282
283}} // namespace detail::variant
284} // namespace boost
285
286#endif // BOOST_VARIANT_DETAIL_VISITATION_IMPL_HPP
Note: See TracBrowser for help on using the repository browser.