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

 

[Gianni Mariani]

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.

You might try a partial specialization "traits" class.


template <typename B> class Traits
{
typedef string OtherConstructorParam;
};

template <> class Traits<string>
{
class Junk OtherConstructorParam;
};


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

 

[Michael Kochetkov]

You might try a partial specialization "traits" class.


template <typename B> class Traits
{
typedef string OtherConstructorParam;
};

template <> class Traits<string>
{
class Junk OtherConstructorParam;
};

Does not it is called explicit specialization?

 

[Gianni Mariani]

Does not it is called explicit specialization?

Yes. My bad.

 

[Michael Kochetkov]

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?

struct string {};
struct B { typedef string Ty; };
struct C { typedef int Ty; };

template<class T, class Ty = typename T::Ty>
struct A : public T {
A(Ty&) {}
};

template<class T>
struct A<T,string> {
A(string&) {}
A(string) {}
};


int
main()
{
A<B> a = string();
A<C> a1 = string(); // This will not compile
}