Question

Here is my code:

template<typename T1, typename T2> class MyClass
{
public:
    template<int num> static int DoSomething();
};

template<typename T1, typename T2> template<int num> int MyClass<T1, T2>::DoSomething()
{
    cout << "This is the common method" << endl;
    cout << "sizeof(T1) = " << sizeof(T1) << endl;
    cout << "sizeof(T2) = " << sizeof(T2) << endl;
    return num;
}

It works well. But when I try to add this

template<typename T1, typename T2> template<> int MyClass<T1, T2>::DoSomething<0>()
{
    cout << "This is ZERO!!!" << endl;
    cout << "sizeof(T1) = " << sizeof(T1) << endl;
    cout << "sizeof(T2) = " << sizeof(T2) << endl;
    return num;
}

I get compiller errors:
invalid explicit specialization before «>» token
template-id «DoSomething<0>» for «int MyClass::DoSomething()» does not match any template declaration

I use g++ 4.6.1
What should I do?

Answer 1

Unfortunately, you can’t specialise a template that’s a member of a class template, without specialising the outer template:

C++11 14.7.3/16: In an explicit specialization declaration for a member of a class template or a member template that appears in namespace scope, the member template and some of its enclosing class templates may remain unspecialized, except that the declaration shall not explicitly specialize a class member template if its enclosing class templates are not explicitly specialized as well.

I think your best option is to add the extra parameter to MyClass, and then partially specialise that.