boost/variant/detail/apply_visitor_delayed.hpp

   1 //-----------------------------------------------------------------------------
   2 // boost variant/detail/apply_visitor_delayed.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_DETAIL_APPLY_VISITOR_DELAYED_HPP
  14 #define BOOST_VARIANT_DETAIL_APPLY_VISITOR_DELAYED_HPP
  15
  16 #include "boost/variant/detail/generic_result_type.hpp"
  17
  18 #include "boost/variant/detail/apply_visitor_unary.hpp"
  19 #include "boost/variant/detail/apply_visitor_binary.hpp"
  20
  21 namespace boost {
  22
  23 //////////////////////////////////////////////////////////////////////////
  24 // function template apply_visitor(visitor)
  25 //
  26 // Returns a function object, overloaded for unary and binary usage, that
  27 // visits its arguments using visitor (or a copy of visitor) via
  28 //  * apply_visitor( visitor, [argument] )
  29 // under unary invocation, or
  30 //  * apply_visitor( visitor, [argument1], [argument2] )
  31 // under binary invocation.
  32 //
  33 // NOTE: Unlike other apply_visitor forms, the visitor object must be
  34 //   non-const; this prevents user from giving temporary, to disastrous
  35 //   effect (i.e., returned function object would have dead reference).
  36 //
  37
  38 template <typename Visitor>
  39 class apply_visitor_delayed_t
  40 {
  41 public: // visitor typedefs
  42
  43     typedef typename Visitor::result_type
  44         result_type;
  45
  46 private: // representation
  47
  48     Visitor& visitor_;
  49
  50 public: // structors
  51
  52     explicit apply_visitor_delayed_t(Visitor& visitor)
  53       : visitor_(visitor)
  54     {
  55     }
  56
  57 public: // unary visitor interface
  58
  59     template <typename Visitable>
  60         BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(result_type)
  61     operator()(Visitable& visitable) const
  62     {
  63         return apply_visitor(visitor_, visitable);
  64     }
  65
  66 public: // binary visitor interface
  67
  68     template <typename Visitable1, typename Visitable2>
  69         BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(result_type)
  70     operator()(Visitable1& visitable1, Visitable2& visitable2) const
  71     {
  72         return apply_visitor(visitor_, visitable1, visitable2);
  73     }
  74
  75 private:
  76     apply_visitor_delayed_t& operator=(const apply_visitor_delayed_t&);
  77
  78 };
  79
  80 template <typename Visitor>
  81 inline apply_visitor_delayed_t<Visitor> apply_visitor(Visitor& visitor)
  82 {
  83     return apply_visitor_delayed_t<Visitor>(visitor);
  84 }
  85
  86 } // namespace boost
  87
  88 #endif // BOOST_VARIANT_DETAIL_APPLY_VISITOR_DELAYED_HPP