Any better way to do this virtual constructor?

[Nan Li]

Hello,
I have the following code now.

enum T1
{ A, B, C };

enum T2
{ D, E, F };


class Base
{
};

template < T1, T2 >
class Derived : public Base
{
} ;

Base * build( T1 t1, T2 t2 )
{
if ( t1 == A and t2 == D )
{
return new Derived<A,D>();
}
if ( t1 == A and t2 == E )
{
return new Derived<A,E>();
}
if ( t1 == A and t2 == F )
{
return new Derived<A,F>();
}
// ..... all the combinations here
}

I really hate to list all the T1-T2 combinations in the 'build'
functions. Is there any better way to code this? t1 and t2 are known
only at run time.

Thanks a lot !

 

[Daniel Pitts]

Hello,
I have the following code now.

enum T1
{ A, B, C };

enum T2
{ D, E, F };


class Base
{
};

template < T1, T2 >
class Derived : public Base
{
} ;

Base * build( T1 t1, T2 t2 )
{
if ( t1 == A and t2 == D )
{
return new Derived<A,D>();
}
if ( t1 == A and t2 == E )
{
return new Derived<A,E>();
}
if ( t1 == A and t2 == F )
{
return new Derived<A,F>();
}
// ..... all the combinations here
}

I really hate to list all the T1-T2 combinations in the 'build'
functions. Is there any better way to code this? t1 and t2 are known
only at run time.

Thanks a lot !

Yes, don't make them template parameters, but member values instead. Is
there a reason that you need different types for this?