muduo庫源碼學習(base):WeakCallback

// Copyright 2010, Shuo Chen.  All rights reserved.
// http://code.google.com/p/muduo/
//
// Use of this source code is governed by a BSD-style license
// that can be found in the License file.
//
// Author: Shuo Chen (chenshuo at chenshuo dot com)

#ifndef MUDUO_BASE_WEAKCALLBACK_H
#define MUDUO_BASE_WEAKCALLBACK_H

#include <functional>
#include <memory>

namespace muduo
{

// A barely usable WeakCallback

#ifdef __GXX_EXPERIMENTAL_CXX0X__

template<typename CLASS, typename... ARGS>
class WeakCallback
{
 public:

  WeakCallback(const std::weak_ptr<CLASS>& object,
               const std::function<void (CLASS*, ARGS...)>& function)
    : object_(object), function_(function)
  {
  }

  // Default dtor, copy ctor and assignment are okay

  void operator()(ARGS&&... args) const
  {
    std::shared_ptr<CLASS> ptr(object_.lock());
    if (ptr)
    {
      function_(ptr.get(), std::forward<ARGS>(args)...);
    }
    // else
    // {
    //   LOG_TRACE << "expired";
    // }
  }

 private:

  std::weak_ptr<CLASS> object_;
  std::function<void (CLASS*, ARGS...)> function_;
};

template<typename CLASS, typename... ARGS>
WeakCallback<CLASS, ARGS...> makeWeakCallback(const std::shared_ptr<CLASS>& object,
                                              void (CLASS::*function)(ARGS...))
{
  return WeakCallback<CLASS, ARGS...>(object, function);
}

template<typename CLASS, typename... ARGS>
WeakCallback<CLASS, ARGS...> makeWeakCallback(const std::shared_ptr<CLASS>& object,
                                              void (CLASS::*function)(ARGS...) const)
{
  return WeakCallback<CLASS, ARGS...>(object, function);
}

#else  // __GXX_EXPERIMENTAL_CXX0X__

// the C++98/03 version doesn't support arguments.

template<typename CLASS>
class WeakCallback//用於保存一個類的函數和這個類的一個對象(智能指針)
{
 public:

  WeakCallback(const std::weak_ptr<CLASS>& object,//參數就是智能指針。
               const std::function<void (CLASS*)>& function)//這是成員函數的仿函數，默認保存一個class對象
    : object_(object), function_(function)
  {
  }

  // Default dtor, copy ctor and assignment are okay

  void operator()() const
  {
    std::shared_ptr<CLASS> ptr(object_.lock());//提升到shared_ptr
    if (ptr)
    {
      function_(ptr.get());//執行object_->function_()
    }
    // else
    // {
    //   LOG_TRACE << "expired";
    // }
  }

 private:

  std::weak_ptr<CLASS> object_;
  std::function<void (CLASS*)> function_;
};

template<typename CLASS>
WeakCallback<CLASS> makeWeakCallback(const std::shared_ptr<CLASS>& object,
                                     void (CLASS::*function)())
{
  return WeakCallback<CLASS>(object, function);
}

template<typename CLASS>
WeakCallback<CLASS> makeWeakCallback(const std::shared_ptr<CLASS>& object,
                                     void (CLASS::*function)() const)//const成員函數，注意它的寫法，是class::*funcname
{
  return WeakCallback<CLASS>(object, function);
}

#endif  // __GXX_EXPERIMENTAL_CXX0X__
}

#endif