boost/type_traits/integral_constant.hpp

0001 //  (C) Copyright John Maddock 2015.
0002 //  Use, modification and distribution are subject to the
0003 //  Boost Software License, Version 1.0. (See accompanying file
0004 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0005
0006 #ifndef BOOST_TYPE_TRAITS_INTEGRAL_CONSTANT_HPP
0007 #define BOOST_TYPE_TRAITS_INTEGRAL_CONSTANT_HPP
0008
0009 #include <boost/config.hpp>
0010 #include <boost/detail/workaround.hpp>
0011
0012 #if (BOOST_WORKAROUND(BOOST_MSVC, BOOST_TESTED_AT(1400)) \
0013    || BOOST_WORKAROUND(BOOST_BORLANDC, BOOST_TESTED_AT(0x610)) \
0014    || BOOST_WORKAROUND(__DMC__, BOOST_TESTED_AT(0x840)) \
0015    || BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3202)) \
0016    || BOOST_WORKAROUND(BOOST_INTEL_CXX_VERSION, BOOST_TESTED_AT(810)) )\
0017    || defined(BOOST_MPL_CFG_NO_ADL_BARRIER_NAMESPACE)
0018
0019
0020 namespace boost{
0021    namespace mpl
0022    {
0023       template <bool B> struct bool_;
0024       template <class I, I val> struct integral_c;
0025       struct integral_c_tag;
0026    }
0027 }
0028
0029 #else
0030
0031 namespace mpl_{
0032
0033    template <bool B> struct bool_;
0034    template <class I, I val> struct integral_c;
0035    struct integral_c_tag;
0036 }
0037
0038 namespace boost
0039 {
0040    namespace mpl
0041    {
0042       using ::mpl_::bool_;
0043       using ::mpl_::integral_c;
0044       using ::mpl_::integral_c_tag;
0045    }
0046 }
0047
0048 #endif
0049
0050 namespace boost{
0051
0052    template <class T, T val>
0053    struct integral_constant
0054    {
0055       typedef mpl::integral_c_tag tag;
0056       typedef T value_type;
0057       typedef integral_constant<T, val> type;
0058       static const T value = val;
0059
0060       operator const mpl::integral_c<T, val>& ()const
0061       {
0062          static const char data[sizeof(long)] = { 0 };
0063          static const void* pdata = data;
0064          return *(reinterpret_cast<const mpl::integral_c<T, val>*>(pdata));
0065       }
0066       BOOST_CONSTEXPR operator T()const { return val; }
0067    };
0068
0069    template <class T, T val>
0070    T const integral_constant<T, val>::value;
0071
0072    template <bool val>
0073    struct integral_constant<bool, val>
0074    {
0075       typedef mpl::integral_c_tag tag;
0076       typedef bool value_type;
0077       typedef integral_constant<bool, val> type;
0078       static const bool value = val;
0079
0080       operator const mpl::bool_<val>& ()const
0081       {
0082          static const char data[sizeof(long)] = { 0 };
0083          static const void* pdata = data;
0084          return *(reinterpret_cast<const mpl::bool_<val>*>(pdata));
0085       }
0086       BOOST_CONSTEXPR operator bool()const { return val; }
0087    };
0088
0089    template <bool val>
0090    bool const integral_constant<bool, val>::value;
0091
0092    typedef integral_constant<bool, true> true_type;
0093    typedef integral_constant<bool, false> false_type;
0094
0095 }
0096
0097 #endif