automatic loading plugin factory

[lni]

Hi,

I have a base class for a base plugin factory (BaseFactory), and many derived factories (DerivedFactory). In each DerivedFactory, there is a static singleton DerivedFactory::instance() as in the following code

class BaseFactory : public QObject 
{
};
 
class DerivedFactory : public BaseFactory
{
public:
 
  virtual ~DerivedFactory();
  static const DerivedFactory& instance();
 
private:
 
  DerivedFactory();
};

class BaseFactory : public QObject 
{
};

class DerivedFactory : public BaseFactory
{
public:

  virtual ~DerivedFactory();
  static const DerivedFactory& instance();

private:

  DerivedFactory();
};

To copy to clipboard, switch view to plain text mode 

Each DerivedFactory::instance() needed to be called immediately after the QApplication is created so the factory is ready to produce object base on class name.

The problem is I have quite a few of those factories, so I hope to force programmers to register the derived factory into the base by some macros, so the base factory will call all DerivedFactory::instance() in one go. This will also avoid some derived factory not be initialized, causing program to crash when restoring previously saved session (because factory has not loaded the plugin yet).

I try following way, and obviously, the function prototype does not match. How can I achieve this goal? Many thanks!

class BaseFactory : public QObject 
{
  typedef const BaseFactory& (FactoryReg)();
 
  /// register the factory to be called by loadAllFactories
  static int registerFactory( const QString& key, FactoryReg* );
 
  static void loadAllFactories();
 
};
 
#define REGISTER_FACTORY( Key, Func )                            \
  static const BaseFactory& instance = BaseFactory::registerFactory( #Key, Func );
 
class DerivedFactory : public BaseFactory
{
public:
 
  virtual ~DerivedFactory();
  static const DerivedFactory& instance();
 
private:
 
  DerivedFactory();
};
 
// in DerivedFactory C++ file, add this line, but fail to compile of course.
REGISTER_FACTORY( DerivedFactory, DerivedFactory::instance );

class BaseFactory : public QObject 
{
  typedef const BaseFactory& (FactoryReg)();

  /// register the factory to be called by loadAllFactories
  static int registerFactory( const QString& key, FactoryReg* );

  static void loadAllFactories();

};

#define REGISTER_FACTORY( Key, Func )                            \
  static const BaseFactory& instance = BaseFactory::registerFactory( #Key, Func );

class DerivedFactory : public BaseFactory
{
public:

  virtual ~DerivedFactory();
  static const DerivedFactory& instance();

private:

  DerivedFactory();
};

// in DerivedFactory C++ file, add this line, but fail to compile of course.
REGISTER_FACTORY( DerivedFactory, DerivedFactory::instance );

To copy to clipboard, switch view to plain text mode