attempt to partially specialize class by defining a member function template to be different for a certain *class* template parameters

gistfile1.cpp

#include <typeinfo>
#include <string>
 
#include <iostream>
template<typename T> struct A {
    template<typename U>
    A(U u) {
        std::cout << std::string("class template parameter generic, ctor template parameter ") + typeid(u).name() << std::endl;
    }
};
 
struct B {};
 
// Now a special version of the constructor for class pointer arguments only
template<typename T>
template <typename U>
A<T*>::A(U u) {
    std::cout << std::string("class template parameter pointer, function template parameter ") + typeid(u).name() << std::endl;
}
 
 
struct X {};
struct Y {};
 
int main() {
    X x;
    Y y;
    // these should call the default ctor
    A<B> abx(x);
    A<B> aby(y);

    // these should call the (class) specialized version
    A<B*> abpx(x);
    A<B*> abpy(y);
}