1
2#ifndef BOOST_MPL_IF_HPP_INCLUDED
3#define BOOST_MPL_IF_HPP_INCLUDED
4
5// Copyright Aleksey Gurtovoy 2000-2004
6//
7// Distributed under the Boost Software License, Version 1.0.
8// (See accompanying file LICENSE_1_0.txt or copy at
9// http://www.boost.org/LICENSE_1_0.txt)
10//
11// See http://www.boost.org/libs/mpl for documentation.
12
13// $Id$
14// $Date$
15// $Revision$
16
17#include <boost/mpl/aux_/value_wknd.hpp>
18#include <boost/mpl/aux_/static_cast.hpp>
19#include <boost/mpl/aux_/na_spec.hpp>
20#include <boost/mpl/aux_/lambda_support.hpp>
21#include <boost/mpl/aux_/config/integral.hpp>
22#include <boost/mpl/aux_/config/ctps.hpp>
23#include <boost/mpl/aux_/config/workaround.hpp>
24
25namespace boost { namespace mpl {
26
27#if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
28
29template<
30 bool C
31 , typename T1
32 , typename T2
33 >
34struct if_c
35{
36 typedef T1 type;
37};
38
39template<
40 typename T1
41 , typename T2
42 >
43struct if_c<false,T1,T2>
44{
45 typedef T2 type;
46};
47
48// agurt, 05/sep/04: nondescriptive parameter names for the sake of DigitalMars
49// (and possibly MWCW < 8.0); see http://article.gmane.org/gmane.comp.lib.boost.devel/108959
50template<
51 typename BOOST_MPL_AUX_NA_PARAM(T1)
52 , typename BOOST_MPL_AUX_NA_PARAM(T2)
53 , typename BOOST_MPL_AUX_NA_PARAM(T3)
54 >
55struct if_
56{
57 private:
58 // agurt, 02/jan/03: two-step 'type' definition for the sake of aCC
59 typedef if_c<
60#if defined(BOOST_MPL_CFG_BCC_INTEGRAL_CONSTANTS)
61 BOOST_MPL_AUX_VALUE_WKND(T1)::value
62#else
63 BOOST_MPL_AUX_STATIC_CAST(bool, BOOST_MPL_AUX_VALUE_WKND(T1)::value)
64#endif
65 , T2
66 , T3
67 > almost_type_;
68
69 public:
70 typedef typename almost_type_::type type;
71
72 BOOST_MPL_AUX_LAMBDA_SUPPORT(3,if_,(T1,T2,T3))
73};
74
75#else
76
77// no partial class template specialization
78
79namespace aux {
80
81template< bool C >
82struct if_impl
83{
84 template< typename T1, typename T2 > struct result_
85 {
86 typedef T1 type;
87 };
88};
89
90template<>
91struct if_impl<false>
92{
93 template< typename T1, typename T2 > struct result_
94 {
95 typedef T2 type;
96 };
97};
98
99} // namespace aux
100
101template<
102 bool C_
103 , typename T1
104 , typename T2
105 >
106struct if_c
107{
108 typedef typename aux::if_impl< C_ >
109 ::template result_<T1,T2>::type type;
110};
111
112// (almost) copy & paste in order to save one more
113// recursively nested template instantiation to user
114template<
115 typename BOOST_MPL_AUX_NA_PARAM(C_)
116 , typename BOOST_MPL_AUX_NA_PARAM(T1)
117 , typename BOOST_MPL_AUX_NA_PARAM(T2)
118 >
119struct if_
120{
121 enum { msvc_wknd_ = BOOST_MPL_AUX_MSVC_VALUE_WKND(C_)::value };
122
123 typedef typename aux::if_impl< BOOST_MPL_AUX_STATIC_CAST(bool, msvc_wknd_) >
124 ::template result_<T1,T2>::type type;
125
126 BOOST_MPL_AUX_LAMBDA_SUPPORT(3,if_,(C_,T1,T2))
127};
128
129#endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
130
131BOOST_MPL_AUX_NA_SPEC(3, if_)
132
133}}
134
135#endif // BOOST_MPL_IF_HPP_INCLUDED
136

source code of boost/boost/mpl/if.hpp