类模板实例化为类型模板参数，语法？

Question

class XY{};

template<typename typeA>
class A
{
(...)
};
template<typename typeB>
class B
{
(...)
};
(...)
     B<class <class XY>A> * attribute; // <- How can I do that without Syntaxerror

When trying this gcc gives me the following error:

xy.h:19: error: template argument 1 is invalid

How can I avoid that?

Answer 1

The class keyword is only for defining a template class, not for declaring an object. For that, you just need:

B<A<XY> >* attribute;

Or to spread it out for clarity:

typedef A<XY> MyA;
typedef B<MyA> MyB;
MyB* attribute;

Answer 2

Your question is quite unclear, but I think you're after template template parameters . This way :

template <template <class> class U>
class Foo {};

Now Foo is a class template accepting another class template as its parameter, like so :

template <class V>
class Bar {};

Foo<Bar> theFoo;