Unable to access protected member of another instance from scope type

Question

In this answer to the question “Why can't my object protect the protected members of another object defined in a common base class?”, You can read:

Access to protected members is available only from their own instance of the base class.

Either I don't get it right, or after MCVE (live on coliru) proves it wrong:

struct Base           { void f(); protected: int prot; };
struct Derived : Base { void g(); private:   int priv; };

void Base::f()
{
    Base b;
    b.prot = prot;
    (void) b;
}

void Derived::g()
{
    {
        Derived d;
        (void) d.priv;
    }

    {
        Derived& d = *this;
        (void) d.priv;
    }

    {
        Derived d;
        (void) d.prot; // <-- access to other instance protected member
    }

    {
        Derived& d = *this;
        (void) d.prot;
    }

    // ---

    {
        Base b;
        (void) b.prot; // error: 'int Base::prot' is protected within this context
    }

    {
        Base& b = *this;
        (void) b.prot; // error: 'int Base::prot' is protected within this context
    }
}

: , Derived, Derived, , Base, , , , Derived Base? Tl; dr: protected "private" private ?

:

• , ;
• .

Answer 1

[class.access.base]:

m R, N, [...]

• m N , R N P, N, m P public, private protected

. :

• R . d.prot - Derived, Derived.
• R , . b.prot - , prot .

, Derived Base , , . , Base. , , Base SomeOtherDerived, , .