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2011-07-16T18:34:12.020
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2011-07-16T18:40:26.637
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One of the cases where I applied the "friend classes", is where one class is composed or referenced by other (objects) classes, and the composing objects, require access to the internals of the main class. <pre><code>enum MyDBTableButtonBarButtonKind { GoFirst, GoPrior, GoNext, GoLast } class MyDBTableButtonBarButtonWidget; class MyDBTableButtonBarWidget { friend class MyDBTableButtonBarButtonWidget; // friend access method: protected: void GoFirst(); void GoPrior(); void GoNext(); void GoLast(); void DoAction(MyDBTableButtonBarButtonKind Kind); }; class MyDBTableButtonBarButtonWidget { private: MyDBTableButtonBarWidget* Toolbar; public: MyDBTableButtonBarButtonWidget(MyDBTableButtonBarWidget* AButtonBar) { this ButtonBar = AButtonBar; } MyDBTableButtonBarButtonKind Kind; public: virtual void Click() { Buttonbar->DoAction(this Kind); }; }; void MyDBTableButtonBarWidget::DoAction(MyDBTableButtonBarButtonKind Kind) { switch (Kind) { case MyDBTableButtonBarButtonKind::GoFirst: this.GoFirst(); break; case MyDBTableButtonBarButtonKind::GoLast: this.GoLast(); break; } } </code></pre> In this example, there is a widget control that is a bar composed of buttons, the buttonbar is referenced to a D.B. table, and has several buttons for a specific action, like select the first record of the table, edit, move to the next. In order to do so, each button class has friend access to private & protected methods, of the given control. As previous answer in this post, usually friend classes act a single class, decomposed in several smaller classes. It's not a finished example, its only a general idea.
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