[SOLVED] Template functions

[valandil211]

Hello C++ gurus!

I have some classes that have approximately the same functionality. However, the return type of the functions differ. Let me show you.

@#ifndef ENTSTA_H
#define ENTSTA_H

#include "tests/ent/ent.h"

class EntSta : public Ent
{
Q_OBJECT
public:
static EntSta *Instance();

protected:
explicit EntSta(QWidget *parent =0);

private:
static EntSta *_instance;@

with implementation

@#include "entsta.h"

EntSta *EntSta::_instance = 0;

EntSta *EntSta::Instance()
{
if (_instance == 0)
{
_instance = new EntSta;
}
return _instance;
}

EntSta::EntSta(QWidget *parent):
Ent(parent)
{
}
@

Now, look at the other classes:

@#ifndef ENTRAP_H
#define ENTRAP_H

#include "tests/ent/ent.h"

class EntRap : public Ent
{
Q_OBJECT
public:
static EntRap *Instance();

protected:
explicit EntRap(QWidget *parent = 0);

signals:

public slots:

private:
static EntRap *_instance;

};@

with implementation

#endif // ENTRAP_H

@#include "entrap.h"

EntRap *EntRap::_instance = 0;

EntRap *EntRap::Instance()
{
if (_instance == 0)
{
_instance = new EntRap;
}
return _instance;
}

EntRap::EntRap(QWidget *parent) :
Ent(parent)
{
}
@

Identical, except return types. Is there a way I could streamline these classes? I read about function templates a bit, but I don't understand how I could use them to solve my problem.

Thanks in advance!

[giesbert]

Hi,

as the classes seem to be QObject / QWidget deribved, you can't use templates.

[valandil211]

Any other way to streamline the process?

[koahnig]

You could return a pointer to the base class. Or is this a problem because it is static? What are you trying to achieve?

Edit: Take it back. Sorry, is getting late.

[valandil211]

I am using the Singleton design pattern from Design Patterns: Elements of Reusable Object-Oriented Software. Moreover, each of these classes is a factory that will instantiate objects in subclasses. Hence, I only want one factory to be instantiated.

Now, the Singleton pattern has the same structure for all classes. I just wanted to know if there was a way to promote code reuse.

Thanks!

[giesbert]

you can use some tricks that MS uses in ATL:

multiple inheritance with templates that know their derived classes. It works but is a bit tricked...

[valandil211]

Thank you, I will look into it.