ceph/src/boost/libs/log/example/doc/util_dynamic_type_disp.cpp

   1 /*
   2  *          Copyright Andrey Semashev 2007 - 2015.
   3  * Distributed under the Boost Software License, Version 1.0.
   4  *    (See accompanying file LICENSE_1_0.txt or copy at
   5  *          http://www.boost.org/LICENSE_1_0.txt)
   6  */
   7
   8 #include <cassert>
   9 #include <cstddef>
  10 #include <string>
  11 #include <iostream>
  12 #include <boost/log/utility/type_dispatch/dynamic_type_dispatcher.hpp>
  13
  14 namespace logging = boost::log;
  15
  16 // Base interface for the custom opaque value
  17 struct my_value_base
  18 {
  19     virtual ~my_value_base() {}
  20     virtual bool dispatch(logging::type_dispatcher& dispatcher) const = 0;
  21 };
  22
  23 // A simple attribute value
  24 template< typename T >
  25 struct my_value :
  26     public my_value_base
  27 {
  28     T m_value;
  29
  30     explicit my_value(T const& value) : m_value(value) {}
  31
  32     // The function passes the contained type into the dispatcher
  33     bool dispatch(logging::type_dispatcher& dispatcher) const
  34     {
  35         logging::type_dispatcher::callback< T > cb = dispatcher.get_callback< T >();
  36         if (cb)
  37         {
  38             cb(m_value);
  39             return true;
  40         }
  41         else
  42             return false;
  43     }
  44 };
  45
  46 //[ example_util_dynamic_type_dispatcher
  47 // Visitor functions for the supported types
  48 void on_int(int const& value)
  49 {
  50     std::cout << "Received int value = " << value << std::endl;
  51 }
  52
  53 void on_double(double const& value)
  54 {
  55     std::cout << "Received double value = " << value << std::endl;
  56 }
  57
  58 void on_string(std::string const& value)
  59 {
  60     std::cout << "Received string value = " << value << std::endl;
  61 }
  62
  63 logging::dynamic_type_dispatcher disp;
  64
  65 // The function initializes the dispatcher object
  66 void init_disp()
  67 {
  68     // Register type visitors
  69     disp.register_type< int >(&on_int);
  70     disp.register_type< double >(&on_double);
  71     disp.register_type< std::string >(&on_string);
  72 }
  73
  74 // Prints the supplied value
  75 bool print(my_value_base const& val)
  76 {
  77     return val.dispatch(disp);
  78 }
  79 //]
  80
  81 int main(int, char*[])
  82 {
  83     init_disp();
  84
  85     // These two attributes are supported by the dispatcher
  86     bool res = print(my_value< std::string >("Hello world!"));
  87     assert(res);
  88
  89     res = print(my_value< double >(1.2));
  90     assert(res);
  91
  92     // This one is not
  93     res = print(my_value< float >(-4.3f));
  94     assert(!res);
  95
  96     return 0;
  97 }