Class members of explicit specializations

A member of an explicitly specialized class is not implicitly instantiated from the member declaration of the primary template. You have to explicitly define members of a class template specialization. You define members of an explicitly specialized template class as you would normal classes, without the template<> prefix. In addition, you can define the members of an explicit specialization inline; no special template syntax is used in this case. The following example demonstrates a class template specialization:

template<class T> class A {
   public:
      void f(T);
};

template<> class A<int> {
   public:
      int g(int);
};

int A<int>::g(int arg) { return 0; }

int main() {
   A<int> a;
   a.g(1234);
}

The explicit specialization A<int> contains the member function g(), which the primary template does not.

If you explicitly specialize a template, a member template, or the member of a class template, then you must declare this specialization before that specialization is implicitly instantiated. For example, the compiler will not allow the following code:

template<class T> class A { };

void f() { A<int> x; }
template<> class A<int> { };

int main() { f(); }

The compiler will not allow the explicit specialization template<> class A<int> { }; because function f() uses this specialization (in the construction of x) before the specialization.