boost/mpl/if.hpp

0001
0002 #ifndef BOOST_MPL_IF_HPP_INCLUDED
0003 #define BOOST_MPL_IF_HPP_INCLUDED
0004
0005 // Copyright Aleksey Gurtovoy 2000-2004
0006 //
0007 // Distributed under the Boost Software License, Version 1.0.
0008 // (See accompanying file LICENSE_1_0.txt or copy at
0009 // http://www.boost.org/LICENSE_1_0.txt)
0010 //
0011 // See http://www.boost.org/libs/mpl for documentation.
0012
0013 // $Id$
0014 // $Date$
0015 // $Revision$
0016
0017 #include <boost/mpl/aux_/value_wknd.hpp>
0018 #include <boost/mpl/aux_/static_cast.hpp>
0019 #include <boost/mpl/aux_/na_spec.hpp>
0020 #include <boost/mpl/aux_/lambda_support.hpp>
0021 #include <boost/mpl/aux_/config/integral.hpp>
0022 #include <boost/mpl/aux_/config/ctps.hpp>
0023 #include <boost/mpl/aux_/config/workaround.hpp>
0024
0025 namespace boost { namespace mpl {
0026
0027 #if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
0028
0029 template<
0030       bool C
0031     , typename T1
0032     , typename T2
0033     >
0034 struct if_c
0035 {
0036     typedef T1 type;
0037 };
0038
0039 template<
0040       typename T1
0041     , typename T2
0042     >
0043 struct if_c<false,T1,T2>
0044 {
0045     typedef T2 type;
0046 };
0047
0048 // agurt, 05/sep/04: nondescriptive parameter names for the sake of DigitalMars
0049 // (and possibly MWCW < 8.0); see https://lists.boost.org/Archives/boost/2004/09/71383.php
0050 template<
0051       typename BOOST_MPL_AUX_NA_PARAM(T1)
0052     , typename BOOST_MPL_AUX_NA_PARAM(T2)
0053     , typename BOOST_MPL_AUX_NA_PARAM(T3)
0054     >
0055 struct if_
0056 {
0057  private:
0058     // agurt, 02/jan/03: two-step 'type' definition for the sake of aCC
0059     typedef if_c<
0060 #if defined(BOOST_MPL_CFG_BCC_INTEGRAL_CONSTANTS)
0061           BOOST_MPL_AUX_VALUE_WKND(T1)::value
0062 #else
0063           BOOST_MPL_AUX_STATIC_CAST(bool, BOOST_MPL_AUX_VALUE_WKND(T1)::value)
0064 #endif
0065         , T2
0066         , T3
0067         > almost_type_;
0068
0069  public:
0070     typedef typename almost_type_::type type;
0071
0072     BOOST_MPL_AUX_LAMBDA_SUPPORT(3,if_,(T1,T2,T3))
0073 };
0074
0075 #else
0076
0077 // no partial class template specialization
0078
0079 namespace aux {
0080
0081 template< bool C >
0082 struct if_impl
0083 {
0084     template< typename T1, typename T2 > struct result_
0085     {
0086         typedef T1 type;
0087     };
0088 };
0089
0090 template<>
0091 struct if_impl<false>
0092 {
0093     template< typename T1, typename T2 > struct result_
0094     {
0095         typedef T2 type;
0096     };
0097 };
0098
0099 } // namespace aux
0100
0101 template<
0102       bool C_
0103     , typename T1
0104     , typename T2
0105     >
0106 struct if_c
0107 {
0108     typedef typename aux::if_impl< C_ >
0109         ::template result_<T1,T2>::type type;
0110 };
0111
0112 // (almost) copy & paste in order to save one more
0113 // recursively nested template instantiation to user
0114 template<
0115       typename BOOST_MPL_AUX_NA_PARAM(C_)
0116     , typename BOOST_MPL_AUX_NA_PARAM(T1)
0117     , typename BOOST_MPL_AUX_NA_PARAM(T2)
0118     >
0119 struct if_
0120 {
0121     enum { msvc_wknd_ = BOOST_MPL_AUX_MSVC_VALUE_WKND(C_)::value };
0122
0123     typedef typename aux::if_impl< BOOST_MPL_AUX_STATIC_CAST(bool, msvc_wknd_) >
0124         ::template result_<T1,T2>::type type;
0125
0126     BOOST_MPL_AUX_LAMBDA_SUPPORT(3,if_,(C_,T1,T2))
0127 };
0128
0129 #endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
0130
0131 BOOST_MPL_AUX_NA_SPEC(3, if_)
0132
0133 }}
0134
0135 #endif // BOOST_MPL_IF_HPP_INCLUDED