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More Effective C++之引用计数

2012-03-02 07:36 [VC教程] 来源于:
导读:Reference counting让我想起了Java,当如果想用C++来实现Java的能力的话,那Reference counting必不可少。Reference counting可以节省程序的运行成本,大量的构

Reference counting让我想起了Java,当如果想用C++来实现Java的能力的话,那Reference counting必不可少。Reference counting可以节省程序的运行成本,大量的构造、析构、分配、释放和拷贝的代价被省略。

实现

classRCObject
{
  public:
   RCObject():refCount(0),shareable(true){}
   RCObject(constRCObject&):refCount(0),shareable(true){}
   RCObject& operator=(constRCObject& rhs){return *this;}
   virtual ~RCObject()=0;
   void AddReference(){++refCount;}
   void RemoveReference(){if (--refCount == 0) deletethis;}
   void markUnshareable(){shareable = false;}
   bool isShareable() const{returnshareable;}
   bool isShared() const {returnrefCount > 1;}
  private:
   int refCount;
   bool shareable;
};
RCObject::~RCObject(){}
template <classT>
class RCPtr
{
  public:
   RCPtr(T* realPtr = 0):pointee(realPtr){init();}
   RCPtr(constRCPtr& rhs):pointee(rhs.pointee){init();}
   ~RCPtr(){if (pointee) pointee->RemoveReference();}
   RCPtr& operator = (constRCPtr& rhs)
   {
    if (pointee!=rhs.pointee)
    {
     if (pointee)
      pointee->RemoveReference();
      pointee = rhs.pointee;
      init();
    }
    return *this;
   }
   T* operator->() const { returnpointee;}
   T& operator*() const{return *pointee;}
  private:
   T* pointee;
   void init()
   {
    if (pointee == 0)
     return;
    if (pointee->isShareable() == false)
     pointee = newT(*pointee);
    pointee->AddReference();
   }
};
class String
{
  public:
   String(const char* value = ""):value(newStringValue(value)){}
   const char& operator[](intnIndex) const
   {
    return value->data[nIndex];
   }
   char& operator[](intnIndex)
   {
    if (value->isShared())
     value = newStringValue(value->data);
     value->markUnshareable();
     returnvalue->data[nIndex];
   }
  protected:
  private:
   struct StringValue:publicRCObject
   {
    char* data;
    String Value(constchar* initValue)
    {
     init(initValue);
    }
    String Value(constStringValue& rhs)
    {
     init(rhs.data);
    }
    void init(constchar * initValue)
    {
     data = newchar[strlen(initValue) + 1];
     strcpy(data,initValue);
    }
    ~String Value()
    {
     delete [] data;
    }
   };
   RCPtr<StringValue> value;
};

(编辑:)

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