How to declare template template parameter

Question

Suppose I have two classes Foo1<T> and Foo2<T>.

I then want to create a function bar that takes a reference to a std::vector<Foo1<T>> or to a std::vector<Foo2<T>> but always returns a std::vector<Foo1<T>>:

template<class T, class Y> std::vector<Foo1<T>> bar(std::vector<Y<T>>&)

Sadly but the compiler doesn't like the <Y<T>> bit. One way round this is to provide two overloads but is there a way I can arrange the above so it's correct?

Answer 1

You need template template parameter:

template<class T, template <typename> class Y> 
std::vector<Foo1<T>> bar(std::vector<Y<T>>&) {}