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1 //-----------------------------------------------------------------------------
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2 // boost variant/recursive_wrapper_fwd.hpp header file
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3 // See http://www.boost.org for updates, documentation, and revision history.
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4 //-----------------------------------------------------------------------------
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5 //
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6 // Copyright (c) 2002
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7 // Eric Friedman, Itay Maman
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8 //
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9 // Portions Copyright (C) 2002 David Abrahams
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10 //
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11 // Distributed under the Boost Software License, Version 1.0. (See
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12 // accompanying file LICENSE_1_0.txt or copy at
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13 // http://www.boost.org/LICENSE_1_0.txt)
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14
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15 #ifndef BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP
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16 #define BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP
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17
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18 #include "boost/mpl/aux_/config/ctps.hpp"
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19
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20 #include "boost/mpl/aux_/lambda_support.hpp"
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21
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22 // should be the last #include
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23 #include "boost/type_traits/detail/bool_trait_def.hpp"
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24
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25 namespace boost {
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26
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27 //////////////////////////////////////////////////////////////////////////
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28 // class template recursive_wrapper
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29 //
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30 // Enables recursive types in templates by breaking cyclic dependencies.
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31 //
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32 // For example:
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33 //
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34 // class my;
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35 //
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36 // typedef variant< int, recursive_wrapper<my> > var;
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37 //
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38 // class my {
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39 // var var_;
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40 // ...
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41 // };
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42 //
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43 template <typename T> class recursive_wrapper;
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44
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45 ///////////////////////////////////////////////////////////////////////////////
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46 // metafunction is_recursive_wrapper (modeled on code by David Abrahams)
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47 //
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48 // True iff specified type matches recursive_wrapper<T>.
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49 //
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50
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51 namespace detail {
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52
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53
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54 template <typename T>
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55 struct is_recursive_wrapper_impl
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56 : mpl::false_
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57 {
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58 };
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59
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60 template <typename T>
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61 struct is_recursive_wrapper_impl< recursive_wrapper<T> >
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62 : mpl::true_
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63 {
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64 };
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65
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66
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67 } // namespace detail
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68
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69 BOOST_TT_AUX_BOOL_TRAIT_DEF1(
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70 is_recursive_wrapper
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71 , T
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72 , (::boost::detail::is_recursive_wrapper_impl<T>::value)
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73 )
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74
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75 ///////////////////////////////////////////////////////////////////////////////
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76 // metafunction unwrap_recursive
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77 //
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78 // If specified type T matches recursive_wrapper<U>, then U; else T.
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79 //
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80
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81
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82 template <typename T>
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83 struct unwrap_recursive
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84 {
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85 typedef T type;
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86
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87 BOOST_MPL_AUX_LAMBDA_SUPPORT(1,unwrap_recursive,(T))
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88 };
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89
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90 template <typename T>
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91 struct unwrap_recursive< recursive_wrapper<T> >
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92 {
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93 typedef T type;
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94
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95 BOOST_MPL_AUX_LAMBDA_SUPPORT_SPEC(1,unwrap_recursive,(T))
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96 };
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97
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98
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99 } // namespace boost
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100
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101 #include "boost/type_traits/detail/bool_trait_undef.hpp"
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102
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103 #endif // BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP
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