C++ How can achieve this Interface configuration? - c++

Question

I certainly don't know how to title this question, sorry.
I'm having some problems to design the following system.
I need a class which will make some work, but this work can be done in a bunch of different ways, say that this work will be made through "drivers".
These drivers can have different interfaces and because of that I need to build a wrapper for each driver.
So I got (or I need) this:
Me ---> MainClass ----> Wrapper ----> Drivers
MainClass is the class I will touch and will call the drivers methods through different wrappers.
Here an example of usage:
MainClass worker;
worker.set_driver("driver_0");
worker.start_process(); //Start process calls a wrapper method which calls a driver's method.
To achieve this I made an interface class:
class Driver_Interface : public QObject
{
Q_OBJECT
public:
Driver_Interface(QObject* parent=0) : QObject(parent){}
virtual bool open()=0;
virtual bool close()=0;
virtual bool write()=0;
virtual bool set_config()=0;
};
A driver wrapper has this shape:
class Driver0 : public Driver_Interface
{
Q_OBJECT
public:
Driver0( QObject* parent=0);
Driver0();
bool open();
bool close();
bool write();
bool set_config();
};
Finally here comes the conflicting point, defining the MainClass:
I would like to avoid to create one member for each wrapper, so I tried this, and right now compiler doesn't complains:
class MainClass
{
public:
MainClass();
~MainClass();
void init();
void set_driver( const QString& );
void start_process();
protected:
QString driver_str;
Driver_Interface* driver; //!<--- Here Here!!!
};
When setting the driver chosen, I do this:
if( driver_str.compare("driver_0")==0 )
this->driver = new Driver_0();
Is this a valid C++ configuration or will I have problems sooner or later?
Basically, what worries me is the creation of the driver of a different type from Driver_Interface, I'm seeing that it casts automatically and no one complains...
Actually I have some problems now compiling, the infamous vtables not defined in Driver_0... does this have some relation with what I want to achieve? UPDATED: I fixed this by deleting the *Driver_Interface* constructor.

Answer 1

To me your basic idea seems to be fine. I would consider separating the creation of drivers into a factory (or at least a factory method) though.

Answer 2

This seems reasonable to me. Having a FactoryMethod or class (AbstractFactory) that creates an object of the required concrete subclass based on some config value is a common pattern.
You could consider having the MainClass implement something like
DriverInterface* createDriver(const string& driverType)
instead of encapsulating the resulting concrete DriverInterface subclass in MainClass. But if you only ever want one concrete DriverInterface instance, the above looks fine.

Answer 3

I would pass "driver_0" to the constructor, and call MainClass::set_driver from there. You can then make MainClass::set_driver private unless you need to change drivers.