Re: constructor or factory or builder

David Bellot wrote:


This is not really the factory method design pattern as defined by the
GoF. It's just using factory objects.


This is not really a C++ language question. You probably want to ask in
comp.object.

But to give you a common example in C++, you can use different
look-and-feels for GUI elements through a factory:

 struct AbstractButton
 {
   virtual ~AbstractButton() {}
   //...
 };

 struct AbstractFactory
 {
   virtual ~AbstractFactory() {}
   virtual std::auto_ptr<AbstractButton> CreateButton() const = 0;
   // ...
 };

 struct SquareButton : AbstractButton { /*...*/ };
 struct RoundedButton : AbstractButton { /*...*/ };

 struct SquareFactory : AbstractFactory
 {
   std::auto_ptr<AbstractButton> CreateButton() const
   {
     return auto_ptr<AbstractButton>( new SquareButton );
   }
   // ...
 };

 struct RoundedFactory : AbstractFactory
 {
   std::auto_ptr<AbstractButton> CreateButton() const
   {
     return auto_ptr<AbstractButton>( new RoundedButton );
   }
   // ...
 };

 struct Dialog
 {
   Dialog( const AbstractFactory& factory )
   {
     // ... create and use buttons abstractly, e.g.,
     std::auto_ptr<AbstractButton> button = factory.CreateButton();
     // ... now use AbstractButton's interface here
     // and it will apply to either square or rounded buttons
     // depending on which factory was passed to this constructor
   }
   // ...
 };

For a more sophisticated implementation of this sort of thing, see
chapters 8 and 9 of _Modern C++ Design_.

Cheers! --M