I would like to define a pass-key class (/implement the pass-key idiom) that grants the code written in the body of ‘int main’ the ability to construct the pass-key.

The following is a working (Granting access to a class, “ToolMain.”) example of the pass-key class that I would like to grant ‘int main’ access to construct (Such as the class, “ToolMain,” has access to construct).

Can I ‘friend’ ‘int main,’ in this case?

class InputUpdateKey
{
private:
    /**
        *   A friend of this class may access its private constructors.
        *
        *   A class may permit a type (That is declared here as a friend)
        *   exclusive access to a method by including this class as a function argument.
    */

    friend class ToolMain;

    InputUpdateKey() {}
    InputUpdateKey(const InputUpdateKey&) {}

    InputUpdateKey& operator=(const InputUpdateKey&) = delete;
};