Databases
StackOverflow2013
Postsdbo
POWhat is the use of a C++ class containing an "implementation" and "interface" pointer to itself?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POWhat is the use of a C++ class containing an "implementation" and "interface" pointer to itself?
    primarykey
    data
    text
    <p>I'm studying some source codes and I'm just wondering why a class (or classes) is often implemented this way:</p> <pre><code> class EventHandler { ... EventDispatcher* m_Dispatcher; virtual bool ProcEvent( EventHandler* Sender, int Task, int Event, void* Param ); ... }; class ClassA: public EventHandler { ... ClassA* m_Impl; ClassA* m_Iface; ... public: // virtual functions virtual bool ProcEvent( EventHandler* Sender, int Task, int Event, void* Param ); virtual void OnDataWritten(const PIOResult&) {;} ... // sample functions void SetImplement( ClassA* aImpl ); void SetInterface( ClassA* aIface ); ClassA* GetImplement() { return m_Impl; } ClassA* GetInterface() { return m_Iface; } bool GetData( list& aList ); }; // Implementation of some sample functions; Most of its function contain more // or less the same format as below, with the return m_Impl->XXX having the same // name as the function being defined (e.g. A::XXX) bool ClassA::GetData( list&lt Data &gt& aList ) { if( m_Impl ) return m_Impl->GetData( aList ); else return false; } class ClassAFactory: public EventHandler { private: ClassAFactory* m_Impl; ClassAFactory* m_Iface; protected: virtual ClassA* MakeTransport(); virtual bool ProcEvent( EventHandler* Sender, int Task, int Event, void* Param ); virtual ClassA* CreateClassA() { return 0; } ... }; // In some member function of ClassB (ClassB inherits ClassA) switch( status ) { case 1: GetInterface()->OnDataWritten(); case 2: // ... }; </code></pre> <p>I believe it's for some design pattern but I'm not familiar with it. It could help me understand if I know what it is. Can anyone help me point out which it could be or what is the use of these classes such that it is implemented this way?</p> <p>I think it's for some event handling and used together with some factory but I'm not sure.</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USjasonline
    1. USjasonline
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POWhat is the use of a C++ class containing an "implementation" and "interface" pointer to itself?
      1. USmatt
      1. VTFavorite
    1. COCan you give a bigger hint about how this is used? If I didn't know any better, I would say it's written by someone who has a basic misunderstanding of object-oriented programming. Otherwise, they are unwisely overloading the meanings of some heavily used words.
      singulars
      1. POWhat is the use of a C++ class containing an "implementation" and "interface" pointer to itself?
      1. USJesse Millikan
    2. COThis reminds me of OO hacks done in straight C where you use a pointer to different versions of the same sturct to mirror some OO features.
      singulars
      1. POWhat is the use of a C++ class containing an "implementation" and "interface" pointer to itself?
      1. USrerun
    3. COI've added some more, I hope it helps.
      singulars
      1. POWhat is the use of a C++ class containing an "implementation" and "interface" pointer to itself?
      1. USjasonline
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload