Specialization of template class containing template member is not working

Question

Why is B<int>::bar<int> == true and how to fix this?

Edit: looks like the problem is that B specialization is incorrect

#include <iostream>

template <class T>
struct A {
  static bool foo;
};

template <class T>
struct B {
  template <class U>
  static bool bar;
};

// assigning default values (works as expected)
template <class T>
bool A<T>::foo = true;

template <class T> template <class U>
bool B<T>::bar = true;

// template specialization
template <>
bool A<int>::foo = false; // works as expected

template <> template <class U>
bool B<int>::bar = false; // not working

int main() {
  std::cout << A<char>::foo << '\n';       // 1
  std::cout << A<int>::foo << '\n';        // 0   works fine
  std::cout << B<char>::bar<char> << '\n'; // 1
  std::cout << B<int>::bar<int> << '\n';   // 1   why is it true?
}

looks like for some reason those lines of code are not setting B<int>::bar<int> to false :

template <> template <class U>
bool B<int>::bar = false;

Answer 1

Why is B::bar == true and how to fix this?

Because you've not correctly explicitly specialized bar . In particular, to explicitly specialize bar we have to use 2 template<> s, one for the enclosing class template and the other for bar itself(as it also is a templated).

Thus, to solve this make the following changes:

template <> template <>
bool B<int>::bar<int> = false; // works now
int main() {
  
  std::cout << B<int>::bar<int> << '\n';   // prints 0
}

Working demo