template question

[Marc Schellens]

I have a template like:

template< typename B> class A: public B
{
typedef typename B::Ty Ty;
A( Ty&);

A( string);
};

The latter ctor, I need only for one out of several B
But for one B, B::Ty is a string.

So I get an error message.

Question:
Can I define a ctor for only one special A<B> ?
If not is there another solution?

thanks,
marc