Out-of-class-template member template specialization syntax

[BigMan]

How do I specialize a member template of a class template out of the
definition of the class template.

 

[davi.reis]

How do I specialize a member template of a class template out of the
definition of the class template.

You can't. You need to specialize the whole stuff. Like

template <> template <>
void X<int>::f<int>() {}

I am not sure if even that can be done. Just do a search in the
archives and you will see a lot of answers.