NULL template?

[Espen Ruud Schultz]

I have a template with some common functions:

template< class Type > class Object : public Type {

public:

void Function( void );

};

Sometimes it makes sence to run Function() without specifying a Type. Is it
possible to create an object out of Object that doesn't inherit like this
template does. Darn, not easy to explain. I wanna do something like this:

Object< NULL >::Function() ;

....and this:

Object< NULL > This;
This.Function() ;

TIA!

, Espen

[Gianni Mariani]

Re: NULL template?

Espen Ruud Schultz wrote:[color=blue]
> I have a template with some common functions:
>
> template< class Type > class Object : public Type {
>
> public:
>
> void Function( void );
>
> };
>
> Sometimes it makes sence to run Function() without specifying a Type.[/color]

This is where I loose you.

The above template says that function is dependant on type and then you
say it's not.

Anyhow, while I don't really know how to help you you might find some
ideas in partial template specializations .

Is it[color=blue]
> possible to create an object out of Object that doesn't inherit like this
> template does. Darn, not easy to explain. I wanna do something like this:
>
> Object< NULL >::Function() ;
>
> ...and this:
>
> Object< NULL > This;
> This.Function() ;
>[/color]

This might be what you're looking for.

BTW - NULL explands to 0 - you can't use Object< NULL >.



#include <iostream>

template <typename Type> class Object : public Type
{
public:

void Function()
{
std::cout << "Basic template\n";
}
};

class SomeClass
{
};

class NULLCLASS
{
};


template <> class Object<NULLCLAS S>
{
public:

void Function()
{
std::cout << "NULLCLASS\ n";
}
};



int main()
{

Object< SomeClass > foo_some;

Object< NULLCLASS > foo_null;


foo_some.Functi on();
foo_null.Functi on();

return 0;
}

[Espen Ruud Schultz]

Re: NULL template?

"Gianni Mariani" <gi2nospam@mari ani.ws> wrote in message
news:bhm1t1$m4n @dispatch.conce ntric.net[color=blue]
>
> This is where I loose you.
>
> The above template says that function is dependant on type and then you
> say it's not.
>[/color]

Maybe this example will help you understand:

class TypeBMP {

public:

Load( filename );
Save( filename );

};

template< class Type > class Object : public Type {

public:

DoFileExist( filename );

};

int main( void ) {

// Normal operation:

Object< TypeBMP > ObjectBMP;
...
ObjectBMP.DoFil eExist( filename );
ObjectBMP.Save( filename );

// But sometimes I wanna check if a file exists
// without creating a big object:

Object< NULL >::DoFileExis t( filename );

// Or use a general object:

Object< NULL > NullObject;
NullObject.DoFi leExist( filename );

return 0;

}

I guess the only and closest way is to create an empty NULLCLASS as you
suggested...

, Espen

[Gianni Mariani]

Re: NULL template?

Espen Ruud Schultz wrote:[color=blue]
> "Gianni Mariani" <gi2nospam@mari ani.ws> wrote in message
> news:bhm1t1$m4n @dispatch.conce ntric.net
>[/color]
....[color=blue]
>
> I guess the only and closest way is to create an empty NULLCLASS as you
> suggested...
>[/color]

I would not design it this way.

I would have a file object that knows about files and a file type object
that knows how to read files.

This is a classic trying to do too many things in one class problem.

G