//h
template<typename T> struct foo { foo(); };
//cpp
template foo<int>;
template<typename T> foo<T>::foo() {}

//cpp
foo<int> obj; <-- OK

-------------------------------

//h
template<typename T> 
class foo 
{ 
  template<typename T2>
  struct doo
  {
     void method(T a);
  };
};
//cpp
template foo<int>::doo<void*>;

???
template<typename T>::template<T2> doo::method<T2>(T a)
{
}