Question

请指教，我如何解决以下问题 - 我希望有类成员变量boost :: variant类型，其类型来自已定义的mpl类型序列。之后，在main中，我想调用一个方法来调用顺序定义的每个类方法的方法。:)有点复杂，但让我说明一下：

struct worker1
{
   void init()
   {
      std::cout << "Worker1 init called" << std::endl;
   }
};

struct worker2
{
   void init()
   {
      std::cout << "Worker2 init called" << std::endl;
   }
};

typedef mpl::vector< worker1, worker2> workers;

template< typename U> struct process3
{
   process3()
   {
      factory();
   }

   struct factoryrun
   {
      template< typename T > void operator()(T& x)
      {
         std::cout << "Factory entry" << std::endl;
         std::cout << "Type is = " << typeid( T ).name() << std::endl;

         m_t3.push_back( x ); // FAIL!!! :(( Doesn't work
      }
   };

   struct runinit
   {
      template<typename T> void operator()(T& x)
      {
         x.init();
      }
   };

   void init()
   {
      mpl::for_each<U>( runinit() );
   }

   void factory()
   {
      std::cout << "Factory start" << std::endl;
      mpl::for_each<U>( factoryrun() );
   }

   typedef typename boost::make_variant_over< U >::type types; // FAIL!!! Doesn't work because I need to have variant<worker1, worker2> but not variant<workers>
   static std::vector< boost::variant<types> > m_t;
};

template<typename K> std::vector< boost::variant<K> > process<K>::m_t;

int main() {
   process<workers> prs;
   // Here should be called init() for worker1 and worker2   
   prs.init();
   return 0;
}

Answer 1

问题解决了。这样的代码正在运作

typedef mpl::vector< worker1, worker2> workers;

template< typename U> struct process3
{
   process3()
   {
      factory();
   }

   struct factoryrun
   {
      template< typename T > void operator()(T& x)
      {
         std::cout << "Factory entry" << std::endl;
         std::cout << "Type is = " << typeid( T ).name() << std::endl;

         m_t3.push_back( x );
      }
   };

   struct runinit
   {
      template<typename T> void operator()(T& x)
      {
         x.init();
      }
   };

   void init()
   {
      mpl::for_each<U>( runinit() );
   }

   void factory()
   {
      std::cout << "Factory start" << std::endl;
      mpl::for_each<U>( factoryrun() );
   }

   typedef typename boost::make_variant_over< U >::type types;
   typedef std::vector< boost::variant<types> > Vector; // Make typedef to simplify
   static Vector m_t3;

};

template<typename U> typename process3<U>::Vector process3<U>::m_t3;

int main() {
   process3<workers> prs3;
   prs3.init();
 return 0;
}

输出：

Factory start
Factory entry
Type is = 7worker1
Factory entry
Type is = 7worker2
Worker1 init called
Worker2 init called

Answer 2

我很抱歉，但此代码的第一个版本不正确。对于init的每次调用，运行并停止新对象worker1和worker2的创建（每次构造函数os worker1和worker2被调用）。所以m_t3变量是没用的。

Bellow是正确的代码。正如您可能会看到worker1和worker2的构造函数被调用一次。

///////////////////////////////////////////////////////////////////////////////////////////////////////////
//
struct worker1
{
   worker1()
   {
      std::cout << "Worker1 ctor" << std::endl;
   }

   void init()
   {
      std::cout << "Worker1 init called. Object address [" << this << "]" << std::endl;
   }

   void run()
   {
      std::cout << "Worker1 run called. Object address [" << this << "]" << std::endl;
   }

   void stop()
   {
      std::cout << "Worker1 stop called. Object address [" << this << "]" << std::endl;
   }
};

///////////////////////////////////////////////////////////////////////////////////////////////////////////
//
struct worker2
{
   worker2()
   {
      std::cout << "Worker2 ctor" << std::endl;
   }

   void init()
   {
      std::cout << "Worker2 init called. Object address [" << this << "]" << std::endl;
   }

   void run()
   {
      std::cout << "Worker2 run called. Object address [" << this << "]" << std::endl;
   }

   void stop()
   {
      std::cout << "Worker2 stop called. Object address [" << this << "]" << std::endl;
   }

};

typedef mpl::vector< worker1, worker2 > workers;

///////////////////////////////////////////////////////////////////////////////////////////////////////////
//
template< typename U> struct process3
{
   process3()
   {
      factory();
   }

   struct factoryrun
   {
      template< typename T > void operator()(T& x)
      {
         std::cout << "Factory entry" << std::endl;
         std::cout << "Type is = " << typeid( T ).name() << std::endl;

         m_t3.push_back( x );
      }
   };

   void init()
   {
      static init_visitor vis;
      std::for_each( m_t3.begin(), m_t3.end(), boost::apply_visitor( vis ) );
   }

   void run()
   {
      static run_visitor vis;
      std::for_each( m_t3.begin(), m_t3.end(), boost::apply_visitor( vis ) );
   }

   void stop()
   {
      static stop_visitor vis;
      std::for_each( m_t3.begin(), m_t3.end(), boost::apply_visitor( vis ) );
   }

   typedef typename boost::make_variant_over< U >::type types;
   typedef std::vector<types> Vector; // Make typedef to simplify
   static Vector m_t3;

   struct init_visitor: public boost::static_visitor<>
   {
      template <typename T>
      void operator()( T& x )
      {
         std::cout << "Init visitor type=" << typeid(x).name() << std::endl;
         x.init();
       }
   };

   struct run_visitor: public boost::static_visitor<>
   {
     template <typename T>
     void operator()( T& x )
     {
        std::cout << "Run visitor type=" << typeid(x).name() << std::endl;
        x.run();
      }
   };

   struct stop_visitor: public boost::static_visitor<>
   {
     template <typename T>
     void operator()( T& x )
     {
        std::cout << "Stop visitor type=" << typeid(x).name() << std::endl;
        x.stop();
      }
   };
};

template<typename K> typename process3<K>::Vector process3<K>::m_t3;

int main() {
   process3<workers> prs3;
   prs3.init();
   prs3.run();
   prs3.stop();
   return 0;
}

输出：

Factory start
Worker1 ctor
Factory entry
Type is = 7worker1
Worker2 ctor
Factory entry
Type is = 7worker2
Init visitor type=7worker1
Worker1 init called. Object address [0x21bf038]
Init visitor type=7worker2
Worker2 init called. Object address [0x21bf048]
Run visitor type=7worker1
Worker1 run called. Object address [0x21bf038]
Run visitor type=7worker2
Worker2 run called. Object address [0x21bf048]
Stop visitor type=7worker1
Worker1 stop called. Object address [0x21bf038]
Stop visitor type=7worker2
Worker2 stop called. Object address [0x21bf048]

mpl类型序列的变体作为类成员 - 如何？

2 个答案: