Question

There is a class Test:

typedef enum
{
    AA, BB
} TType;

template <typename T>
struct TVector
{
    typedef std::vector <T> Type;
};

template < typename T, const TType type >
class Test
{
private:
            typename TVector <T>::Type it; 
};

and its specialization with redefined operator = (there with no additional functionality):

template < typename T, const TType type >
class Test <T *, type> 
{
public:
    Test <T *, type > & operator = ( const Test <T*, type > &source ) {return *this;}

            template <TType type2>
    Test <T *, type > & operator = ( const Test <T*, type2 > &source ){return *this;}

            template <TType type2>
    Test <T *, type > * operator = ( const Test <T*, type2 > *source ) {return *this;}
};

I am trying to assign objects with different TType parameter each other, and this step works correctly.

int _tmain(int argc, _TCHAR* argv[])
{
Test <double *, AA> a1;
Test <double *, BB> b1;

a1=b1;  //Correct

Test <double *, AA> *a2;
Test <double *, BB> *b2;

a2 = b2;  //Error

return 0;
}

But the same step with pointers does not work, see the error code:

Error   1   error C2440: '=' : cannot convert from 'Test<T,type> *' to 'Test<T,type> *' 49

Is it possible to assign pointers with different TType parameter each other (how?) or not?

Updated question:

And what about assignment between pointers and objects?

a2 = &b1;  //Error
*a2 = b1;  //Unitialized memory

Could I ask for a code sample?
Thanks for your help.

Answer 1

The second example does not work because you are not assigning to the object, you are assigning to a pointer. It’s the same reason that this does not work:

int * a;
float * b;

b = a;

Even though a float can be assigned from an int, a pointer to float cannot be assigned from a pointer to int.

Try *a2 = b2 or *a2 = *b2 instead — your operators should catch both of those.

Note also that this implementation appears to be wrong:

template <TType type2>
Test <T *, type > * operator = ( const Test <T*, type2 > *source )
{
    return *this;
}

The this implicit variable is already a pointer type, so you need to return this, not return *this. I would suggest eliminating this overload of the assignment operator completely, since it is bound to be more confusing than it will be useful.