boost/variant/visitor_ptr.hpp

   1 //-----------------------------------------------------------------------------
   2 // boost variant/visitor_ptr.hpp header file
   3 // See http://www.boost.org for updates, documentation, and revision history.
   4 //-----------------------------------------------------------------------------
   5 //
   6 // Copyright (c) 2002-2003
   7 // Eric Friedman
   8 //
   9 // Distributed under the Boost Software License, Version 1.0. (See
  10 // accompanying file LICENSE_1_0.txt or copy at
  11 // http://www.boost.org/LICENSE_1_0.txt)
  12
  13 #ifndef BOOST_VARIANT_VISITOR_PTR_HPP
  14 #define BOOST_VARIANT_VISITOR_PTR_HPP
  15
  16 #include "boost/variant/bad_visit.hpp"
  17 #include "boost/variant/static_visitor.hpp"
  18
  19 #include "boost/mpl/eval_if.hpp"
  20 #include "boost/mpl/identity.hpp"
  21 #include "boost/type_traits/add_reference.hpp"
  22 #include "boost/type_traits/is_reference.hpp"
  23 #include "boost/type_traits/is_void.hpp"
  24
  25 namespace boost {
  26
  27 //////////////////////////////////////////////////////////////////////////
  28 // function template visitor_ptr
  29 //
  30 // Adapts a function pointer for use as visitor capable of handling
  31 // values of a single type. Throws bad_visit if inappropriately applied.
  32 //
  33 template <typename T, typename R>
  34 class visitor_ptr_t
  35     : public static_visitor<R>
  36 {
  37 private: // representation
  38
  39     typedef R (*visitor_t)(T);
  40
  41     visitor_t visitor_;
  42
  43 public: // typedefs
  44
  45     typedef R result_type;
  46
  47 private: // private typedefs
  48
  49     typedef typename mpl::eval_if<
  50           is_reference<T>
  51         , mpl::identity<T>
  52         , add_reference<const T>
  53         >::type argument_fwd_type;
  54
  55 public: // structors
  56
  57     explicit visitor_ptr_t(visitor_t visitor)
  58       : visitor_(visitor)
  59     {
  60     }
  61
  62 public: // static visitor interfaces
  63
  64     template <typename U>
  65     result_type operator()(const U&) const
  66     {
  67         throw bad_visit();
  68     }
  69
  70 #if !defined(BOOST_NO_VOID_RETURNS)
  71
  72 public: // static visitor interfaces, cont.
  73
  74     result_type operator()(argument_fwd_type operand) const
  75     {
  76         return visitor_(operand);
  77     }
  78
  79 #else // defined(BOOST_NO_VOID_RETURNS)
  80
  81 private: // helpers, for static visitor interfaces (below)
  82
  83     result_type execute_impl(argument_fwd_type operand, mpl::false_) const
  84     {
  85         return visitor_(operand);
  86     }
  87
  88         BOOST_VARIANT_AUX_RETURN_VOID_TYPE
  89     execute_impl(argument_fwd_type operand, mpl::true_) const
  90     {
  91         visitor_(operand);
  92         BOOST_VARIANT_AUX_RETURN_VOID;
  93     }
  94
  95 public: // static visitor interfaces, cont.
  96
  97         BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(result_type)
  98     operator()(argument_fwd_type operand) const
  99     {
 100         typedef typename is_void<result_type>::type has_void_result;
 101         return execute_impl(operand, has_void_result());
 102     }
 103
 104 #endif // BOOST_NO_VOID_RETURNS workaround
 105
 106 };
 107
 108 template <typename R, typename T>
 109 inline visitor_ptr_t<T,R> visitor_ptr(R (*visitor)(T))
 110 {
 111     return visitor_ptr_t<T,R>(visitor);
 112 }
 113
 114 } // namespace boost
 115
 116 #endif// BOOST_VISITOR_VISITOR_PTR_HPP