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1 // Boost enable_if library
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2
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3 // Copyright 2003 (c) The Trustees of Indiana University.
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4
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5 // Use, modification, and distribution is subject to the Boost Software
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6 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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7 // http://www.boost.org/LICENSE_1_0.txt)
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8
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9 // Authors: Jaakko Jarvi (jajarvi at osl.iu.edu)
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10 // Jeremiah Willcock (jewillco at osl.iu.edu)
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11 // Andrew Lumsdaine (lums at osl.iu.edu)
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12
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13
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14 #ifndef BOOST_CORE_ENABLE_IF_HPP
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15 #define BOOST_CORE_ENABLE_IF_HPP
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16
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17 #include "boost/config.hpp"
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18
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19 // Even the definition of enable_if causes problems on some compilers,
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20 // so it's macroed out for all compilers that do not support SFINAE
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21
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22 #ifndef BOOST_NO_SFINAE
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23
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24 namespace boost
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25 {
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26
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27 template <bool B, class T = void>
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28 struct enable_if_c {
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29 typedef T type;
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30 };
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31
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32 template <class T>
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33 struct enable_if_c<false, T> {};
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34
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35 template <class Cond, class T = void>
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36 struct enable_if : public enable_if_c<Cond::value, T> {};
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37
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38 template <bool B, class T>
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39 struct lazy_enable_if_c {
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40 typedef typename T::type type;
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41 };
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42
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43 template <class T>
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44 struct lazy_enable_if_c<false, T> {};
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45
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46 template <class Cond, class T>
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47 struct lazy_enable_if : public lazy_enable_if_c<Cond::value, T> {};
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48
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49
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50 template <bool B, class T = void>
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51 struct disable_if_c {
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52 typedef T type;
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53 };
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54
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55 template <class T>
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56 struct disable_if_c<true, T> {};
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57
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58 template <class Cond, class T = void>
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59 struct disable_if : public disable_if_c<Cond::value, T> {};
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60
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61 template <bool B, class T>
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62 struct lazy_disable_if_c {
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63 typedef typename T::type type;
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64 };
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65
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66 template <class T>
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67 struct lazy_disable_if_c<true, T> {};
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68
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69 template <class Cond, class T>
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70 struct lazy_disable_if : public lazy_disable_if_c<Cond::value, T> {};
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71
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72 } // namespace boost
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73
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74 #else
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75
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76 namespace boost {
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77
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78 namespace detail { typedef void enable_if_default_T; }
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79
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80 template <typename T>
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81 struct enable_if_does_not_work_on_this_compiler;
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82
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83 template <bool B, class T = detail::enable_if_default_T>
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84 struct enable_if_c : enable_if_does_not_work_on_this_compiler<T>
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85 { };
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86
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87 template <bool B, class T = detail::enable_if_default_T>
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88 struct disable_if_c : enable_if_does_not_work_on_this_compiler<T>
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89 { };
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90
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91 template <bool B, class T = detail::enable_if_default_T>
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92 struct lazy_enable_if_c : enable_if_does_not_work_on_this_compiler<T>
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93 { };
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94
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95 template <bool B, class T = detail::enable_if_default_T>
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96 struct lazy_disable_if_c : enable_if_does_not_work_on_this_compiler<T>
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97 { };
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98
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99 template <class Cond, class T = detail::enable_if_default_T>
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100 struct enable_if : enable_if_does_not_work_on_this_compiler<T>
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101 { };
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102
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103 template <class Cond, class T = detail::enable_if_default_T>
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104 struct disable_if : enable_if_does_not_work_on_this_compiler<T>
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105 { };
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106
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107 template <class Cond, class T = detail::enable_if_default_T>
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108 struct lazy_enable_if : enable_if_does_not_work_on_this_compiler<T>
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109 { };
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110
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111 template <class Cond, class T = detail::enable_if_default_T>
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112 struct lazy_disable_if : enable_if_does_not_work_on_this_compiler<T>
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113 { };
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114
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115 } // namespace boost
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116
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117 #endif // BOOST_NO_SFINAE
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118
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119 #endif
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