Is it possible to specialize a method of a template class on another templated class?

Question

I have a class A that is a template, and I want to specialize the method foo() if the class is a std::vector<T> with T generic, I am getting the error: invalid use of incomplete type. I'd like to avoid writing all specializations for all possible vectors.

#include <iostream>
#include <vector>

template<typename V>
struct A {
  void foo() {
    std::cout << "A<V>\n";
  }
};

template<typename T>
void A<std::vector<T>>::foo() {
  std::cout << "A<V<T>>\n";
}

int main() {
  C<int> a;
  C<std::vector<int>> b;

  return 0;
}

Answer 1

Just using c++20 contrians:

template <typename V>
struct A {
  void foo() { std::cout << "A<V>\n"; }

  void foo() requires (std::same_as<V, std::vector<typename V::value_type>>) {
    std::cout << "A<V<T>>\n";
  }
};

Then this works:

A<int>{}.foo(); // call normal one
A<std::vector<int>>{}.foo(); // call specialized one