Overloading operator<< in friend function

[DyslexicChciken]

If I have a template class called object_class, and I want to overload the operator << by using a friend function, I would use the code below within the header file:

template < class ItemType>
class object_class
{

  public:

  ...
  //Why do we need a new template class type for the friend function below?
  template <class friendItemType>
  friend ostream& operator<<(ostream& outputStream, const object_class< friendItemType >& output);

};

If inside the header file, the template class object_class has template type <ItemType>, then my book says I cannot use <ItemType> again in the friend function parameter that overloads operator<< (code above), so I have to create a new template with new type <friendItemType>. This is because operator << is not a part of object_class.

My question is, why does it matter? Isn't <ItemType>, the template type of object_class already an arbitrary type? Why do we need two arbitrary types? And a new template class within another class at that?

[LB]

Templates are weird. If you define template classes completely inline you don't have to worry about some of the weirdness.

template<typename T>
struct MyClass
{
    //...

    friend std::ostream &operator<<(std::ostream &os, MyClass const &mc)
    {
        return os << mc.blah1 << " " << mc.blah2;
    }
};

What is the full name of your book, by the way?

[DyslexicChciken]

What is the full name of your book, by the way?

My book is called Data Abstraction & Problem Solving with C++ walls and mirrors.