the #include test

Suppose we have a class called widget defined in widget.hpp
class widget
{
    ...
};
How many ways can the definition of the class fubar depend on widget?
I can think of thirteen ways:
class fubar : public widget // 1 inheritance
{
    void value_parameter(widget  ); // 2
    void   ref_parameter(widget &); // 3
    void   ptr_parameter(widget *); // 4

    widget value_return(); // 5
    widget & ref_return(); // 6
    widget * ptr_return(); // 7

    widget instance_value_member; //  8
    widget & instance_ref_member; //  9
    widget * instance_ptr_member; // 10

    static widget static_value_member; // 11
    static widget & static_ref_member; // 12
    static widget * static_ptr_member; // 13
};
Now for the test.
Which of the thirteen ways require a hash include
#include "widget.hpp"
as opposed to a forward declaration
class widget;
I've given this test to many many programmers and the vast majority get it wrong. The variety of answers I get is amazing. I recently gave it to a room of about 100 C++ developers and 5 got it right with about 20 different wrong answers (at which point I stopped counting).

What's your answer?
Once you've decided you can scroll down to find the answer.
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The answer is 1 and 8.
How did you do?


If you don't believe me why not try it now in cyber-dojo (click the link and then click the start button).